From 0ec88413f0a04b31149c6850e6938b4b0f33a748 Mon Sep 17 00:00:00 2001 From: Mauro Carvalho Chehab Date: Fri, 12 May 2017 08:14:47 -0300 Subject: [PATCH] docs-rst: convert libata book to ReST Use pandoc to convert documentation to ReST by calling Documentation/sphinx/tmplcvt script. Signed-off-by: Mauro Carvalho Chehab --- Documentation/DocBook/Makefile | 2 +- Documentation/DocBook/libata.tmpl | 1625 ----------------------------------- Documentation/driver-api/index.rst | 1 + Documentation/driver-api/libata.rst | 1027 ++++++++++++++++++++++ 4 files changed, 1029 insertions(+), 1626 deletions(-) delete mode 100644 Documentation/DocBook/libata.tmpl create mode 100644 Documentation/driver-api/libata.rst diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile index 2f767e3..abe7134 100644 --- a/Documentation/DocBook/Makefile +++ b/Documentation/DocBook/Makefile @@ -9,7 +9,7 @@ DOCBOOKS := z8530book.xml \ networking.xml \ lsm.xml \ - libata.xml mtdnand.xml librs.xml rapidio.xml \ + mtdnand.xml librs.xml rapidio.xml \ s390-drivers.xml scsi.xml \ sh.xml w1.xml diff --git a/Documentation/DocBook/libata.tmpl b/Documentation/DocBook/libata.tmpl deleted file mode 100644 index 0320910..0000000 --- a/Documentation/DocBook/libata.tmpl +++ /dev/null @@ -1,1625 +0,0 @@ - - - - - - libATA Developer's Guide - - - - Jeff - Garzik - - - - - 2003-2006 - Jeff Garzik - - - - - The contents of this file are subject to the Open - Software License version 1.1 that can be found at - http://fedoraproject.org/wiki/Licensing:OSL1.1 - and is included herein by reference. - - - - Alternatively, the contents of this file may be used under the terms - of the GNU General Public License version 2 (the "GPL") as distributed - in the kernel source COPYING file, in which case the provisions of - the GPL are applicable instead of the above. If you wish to allow - the use of your version of this file only under the terms of the - GPL and not to allow others to use your version of this file under - the OSL, indicate your decision by deleting the provisions above and - replace them with the notice and other provisions required by the GPL. - If you do not delete the provisions above, a recipient may use your - version of this file under either the OSL or the GPL. - - - - - - - - - Introduction - - libATA is a library used inside the Linux kernel to support ATA host - controllers and devices. libATA provides an ATA driver API, class - transports for ATA and ATAPI devices, and SCSI<->ATA translation - for ATA devices according to the T10 SAT specification. - - - This Guide documents the libATA driver API, library functions, library - internals, and a couple sample ATA low-level drivers. - - - - - libata Driver API - - struct ata_port_operations is defined for every low-level libata - hardware driver, and it controls how the low-level driver - interfaces with the ATA and SCSI layers. - - - FIS-based drivers will hook into the system with ->qc_prep() and - ->qc_issue() high-level hooks. Hardware which behaves in a manner - similar to PCI IDE hardware may utilize several generic helpers, - defining at a bare minimum the bus I/O addresses of the ATA shadow - register blocks. - - - struct ata_port_operations - - Disable ATA port - -void (*port_disable) (struct ata_port *); - - - - Called from ata_bus_probe() error path, as well as when - unregistering from the SCSI module (rmmod, hot unplug). - This function should do whatever needs to be done to take the - port out of use. In most cases, ata_port_disable() can be used - as this hook. - - - Called from ata_bus_probe() on a failed probe. - Called from ata_scsi_release(). - - - - - Post-IDENTIFY device configuration - -void (*dev_config) (struct ata_port *, struct ata_device *); - - - - Called after IDENTIFY [PACKET] DEVICE is issued to each device - found. Typically used to apply device-specific fixups prior to - issue of SET FEATURES - XFER MODE, and prior to operation. - - - This entry may be specified as NULL in ata_port_operations. - - - - - Set PIO/DMA mode - -void (*set_piomode) (struct ata_port *, struct ata_device *); -void (*set_dmamode) (struct ata_port *, struct ata_device *); -void (*post_set_mode) (struct ata_port *); -unsigned int (*mode_filter) (struct ata_port *, struct ata_device *, unsigned int); - - - - Hooks called prior to the issue of SET FEATURES - XFER MODE - command. The optional ->mode_filter() hook is called when libata - has built a mask of the possible modes. This is passed to the - ->mode_filter() function which should return a mask of valid modes - after filtering those unsuitable due to hardware limits. It is not - valid to use this interface to add modes. - - - dev->pio_mode and dev->dma_mode are guaranteed to be valid when - ->set_piomode() and when ->set_dmamode() is called. The timings for - any other drive sharing the cable will also be valid at this point. - That is the library records the decisions for the modes of each - drive on a channel before it attempts to set any of them. - - - ->post_set_mode() is - called unconditionally, after the SET FEATURES - XFER MODE - command completes successfully. - - - - ->set_piomode() is always called (if present), but - ->set_dma_mode() is only called if DMA is possible. - - - - - Taskfile read/write - -void (*sff_tf_load) (struct ata_port *ap, struct ata_taskfile *tf); -void (*sff_tf_read) (struct ata_port *ap, struct ata_taskfile *tf); - - - - ->tf_load() is called to load the given taskfile into hardware - registers / DMA buffers. ->tf_read() is called to read the - hardware registers / DMA buffers, to obtain the current set of - taskfile register values. - Most drivers for taskfile-based hardware (PIO or MMIO) use - ata_sff_tf_load() and ata_sff_tf_read() for these hooks. - - - - - PIO data read/write - -void (*sff_data_xfer) (struct ata_device *, unsigned char *, unsigned int, int); - - - -All bmdma-style drivers must implement this hook. This is the low-level -operation that actually copies the data bytes during a PIO data -transfer. -Typically the driver will choose one of ata_sff_data_xfer_noirq(), -ata_sff_data_xfer(), or ata_sff_data_xfer32(). - - - - - ATA command execute - -void (*sff_exec_command)(struct ata_port *ap, struct ata_taskfile *tf); - - - - causes an ATA command, previously loaded with - ->tf_load(), to be initiated in hardware. - Most drivers for taskfile-based hardware use ata_sff_exec_command() - for this hook. - - - - - Per-cmd ATAPI DMA capabilities filter - -int (*check_atapi_dma) (struct ata_queued_cmd *qc); - - - -Allow low-level driver to filter ATA PACKET commands, returning a status -indicating whether or not it is OK to use DMA for the supplied PACKET -command. - - - This hook may be specified as NULL, in which case libata will - assume that atapi dma can be supported. - - - - - Read specific ATA shadow registers - -u8 (*sff_check_status)(struct ata_port *ap); -u8 (*sff_check_altstatus)(struct ata_port *ap); - - - - Reads the Status/AltStatus ATA shadow register from - hardware. On some hardware, reading the Status register has - the side effect of clearing the interrupt condition. - Most drivers for taskfile-based hardware use - ata_sff_check_status() for this hook. - - - - - Write specific ATA shadow register - -void (*sff_set_devctl)(struct ata_port *ap, u8 ctl); - - - - Write the device control ATA shadow register to the hardware. - Most drivers don't need to define this. - - - - - Select ATA device on bus - -void (*sff_dev_select)(struct ata_port *ap, unsigned int device); - - - - Issues the low-level hardware command(s) that causes one of N - hardware devices to be considered 'selected' (active and - available for use) on the ATA bus. This generally has no - meaning on FIS-based devices. - - - Most drivers for taskfile-based hardware use - ata_sff_dev_select() for this hook. - - - - - Private tuning method - -void (*set_mode) (struct ata_port *ap); - - - - By default libata performs drive and controller tuning in - accordance with the ATA timing rules and also applies blacklists - and cable limits. Some controllers need special handling and have - custom tuning rules, typically raid controllers that use ATA - commands but do not actually do drive timing. - - - - - This hook should not be used to replace the standard controller - tuning logic when a controller has quirks. Replacing the default - tuning logic in that case would bypass handling for drive and - bridge quirks that may be important to data reliability. If a - controller needs to filter the mode selection it should use the - mode_filter hook instead. - - - - - - Control PCI IDE BMDMA engine - -void (*bmdma_setup) (struct ata_queued_cmd *qc); -void (*bmdma_start) (struct ata_queued_cmd *qc); -void (*bmdma_stop) (struct ata_port *ap); -u8 (*bmdma_status) (struct ata_port *ap); - - - -When setting up an IDE BMDMA transaction, these hooks arm -(->bmdma_setup), fire (->bmdma_start), and halt (->bmdma_stop) -the hardware's DMA engine. ->bmdma_status is used to read the standard -PCI IDE DMA Status register. - - - -These hooks are typically either no-ops, or simply not implemented, in -FIS-based drivers. - - -Most legacy IDE drivers use ata_bmdma_setup() for the bmdma_setup() -hook. ata_bmdma_setup() will write the pointer to the PRD table to -the IDE PRD Table Address register, enable DMA in the DMA Command -register, and call exec_command() to begin the transfer. - - -Most legacy IDE drivers use ata_bmdma_start() for the bmdma_start() -hook. ata_bmdma_start() will write the ATA_DMA_START flag to the DMA -Command register. - - -Many legacy IDE drivers use ata_bmdma_stop() for the bmdma_stop() -hook. ata_bmdma_stop() clears the ATA_DMA_START flag in the DMA -command register. - - -Many legacy IDE drivers use ata_bmdma_status() as the bmdma_status() hook. - - - - - High-level taskfile hooks - -void (*qc_prep) (struct ata_queued_cmd *qc); -int (*qc_issue) (struct ata_queued_cmd *qc); - - - - Higher-level hooks, these two hooks can potentially supercede - several of the above taskfile/DMA engine hooks. ->qc_prep is - called after the buffers have been DMA-mapped, and is typically - used to populate the hardware's DMA scatter-gather table. - Most drivers use the standard ata_qc_prep() helper function, but - more advanced drivers roll their own. - - - ->qc_issue is used to make a command active, once the hardware - and S/G tables have been prepared. IDE BMDMA drivers use the - helper function ata_qc_issue_prot() for taskfile protocol-based - dispatch. More advanced drivers implement their own ->qc_issue. - - - ata_qc_issue_prot() calls ->tf_load(), ->bmdma_setup(), and - ->bmdma_start() as necessary to initiate a transfer. - - - - - Exception and probe handling (EH) - -void (*eng_timeout) (struct ata_port *ap); -void (*phy_reset) (struct ata_port *ap); - - - -Deprecated. Use ->error_handler() instead. - - - -void (*freeze) (struct ata_port *ap); -void (*thaw) (struct ata_port *ap); - - - -ata_port_freeze() is called when HSM violations or some other -condition disrupts normal operation of the port. A frozen port -is not allowed to perform any operation until the port is -thawed, which usually follows a successful reset. - - - -The optional ->freeze() callback can be used for freezing the port -hardware-wise (e.g. mask interrupt and stop DMA engine). If a -port cannot be frozen hardware-wise, the interrupt handler -must ack and clear interrupts unconditionally while the port -is frozen. - - -The optional ->thaw() callback is called to perform the opposite of ->freeze(): -prepare the port for normal operation once again. Unmask interrupts, -start DMA engine, etc. - - - -void (*error_handler) (struct ata_port *ap); - - - -->error_handler() is a driver's hook into probe, hotplug, and recovery -and other exceptional conditions. The primary responsibility of an -implementation is to call ata_do_eh() or ata_bmdma_drive_eh() with a set -of EH hooks as arguments: - - - -'prereset' hook (may be NULL) is called during an EH reset, before any other actions -are taken. - - - -'postreset' hook (may be NULL) is called after the EH reset is performed. Based on -existing conditions, severity of the problem, and hardware capabilities, - - - -Either 'softreset' (may be NULL) or 'hardreset' (may be NULL) will be -called to perform the low-level EH reset. - - - -void (*post_internal_cmd) (struct ata_queued_cmd *qc); - - - -Perform any hardware-specific actions necessary to finish processing -after executing a probe-time or EH-time command via ata_exec_internal(). - - - - - Hardware interrupt handling - -irqreturn_t (*irq_handler)(int, void *, struct pt_regs *); -void (*irq_clear) (struct ata_port *); - - - - ->irq_handler is the interrupt handling routine registered with - the system, by libata. ->irq_clear is called during probe just - before the interrupt handler is registered, to be sure hardware - is quiet. - - - The second argument, dev_instance, should be cast to a pointer - to struct ata_host_set. - - - Most legacy IDE drivers use ata_sff_interrupt() for the - irq_handler hook, which scans all ports in the host_set, - determines which queued command was active (if any), and calls - ata_sff_host_intr(ap,qc). - - - Most legacy IDE drivers use ata_sff_irq_clear() for the - irq_clear() hook, which simply clears the interrupt and error - flags in the DMA status register. - - - - - SATA phy read/write - -int (*scr_read) (struct ata_port *ap, unsigned int sc_reg, - u32 *val); -int (*scr_write) (struct ata_port *ap, unsigned int sc_reg, - u32 val); - - - - Read and write standard SATA phy registers. Currently only used - if ->phy_reset hook called the sata_phy_reset() helper function. - sc_reg is one of SCR_STATUS, SCR_CONTROL, SCR_ERROR, or SCR_ACTIVE. - - - - - Init and shutdown - -int (*port_start) (struct ata_port *ap); -void (*port_stop) (struct ata_port *ap); -void (*host_stop) (struct ata_host_set *host_set); - - - - ->port_start() is called just after the data structures for each - port are initialized. Typically this is used to alloc per-port - DMA buffers / tables / rings, enable DMA engines, and similar - tasks. Some drivers also use this entry point as a chance to - allocate driver-private memory for ap->private_data. - - - Many drivers use ata_port_start() as this hook or call - it from their own port_start() hooks. ata_port_start() - allocates space for a legacy IDE PRD table and returns. - - - ->port_stop() is called after ->host_stop(). Its sole function - is to release DMA/memory resources, now that they are no longer - actively being used. Many drivers also free driver-private - data from port at this time. - - - ->host_stop() is called after all ->port_stop() calls -have completed. The hook must finalize hardware shutdown, release DMA -and other resources, etc. - This hook may be specified as NULL, in which case it is not called. - - - - - - - - - Error handling - - - This chapter describes how errors are handled under libata. - Readers are advised to read SCSI EH - (Documentation/scsi/scsi_eh.txt) and ATA exceptions doc first. - - - Origins of commands - - In libata, a command is represented with struct ata_queued_cmd - or qc. qc's are preallocated during port initialization and - repetitively used for command executions. Currently only one - qc is allocated per port but yet-to-be-merged NCQ branch - allocates one for each tag and maps each qc to NCQ tag 1-to-1. - - - libata commands can originate from two sources - libata itself - and SCSI midlayer. libata internal commands are used for - initialization and error handling. All normal blk requests - and commands for SCSI emulation are passed as SCSI commands - through queuecommand callback of SCSI host template. - - - - How commands are issued - - - - Internal commands - - - First, qc is allocated and initialized using - ata_qc_new_init(). Although ata_qc_new_init() doesn't - implement any wait or retry mechanism when qc is not - available, internal commands are currently issued only during - initialization and error recovery, so no other command is - active and allocation is guaranteed to succeed. - - - Once allocated qc's taskfile is initialized for the command to - be executed. qc currently has two mechanisms to notify - completion. One is via qc->complete_fn() callback and the - other is completion qc->waiting. qc->complete_fn() callback - is the asynchronous path used by normal SCSI translated - commands and qc->waiting is the synchronous (issuer sleeps in - process context) path used by internal commands. - - - Once initialization is complete, host_set lock is acquired - and the qc is issued. - - - - - SCSI commands - - - All libata drivers use ata_scsi_queuecmd() as - hostt->queuecommand callback. scmds can either be simulated - or translated. No qc is involved in processing a simulated - scmd. The result is computed right away and the scmd is - completed. - - - For a translated scmd, ata_qc_new_init() is invoked to - allocate a qc and the scmd is translated into the qc. SCSI - midlayer's completion notification function pointer is stored - into qc->scsidone. - - - qc->complete_fn() callback is used for completion - notification. ATA commands use ata_scsi_qc_complete() while - ATAPI commands use atapi_qc_complete(). Both functions end up - calling qc->scsidone to notify upper layer when the qc is - finished. After translation is completed, the qc is issued - with ata_qc_issue(). - - - Note that SCSI midlayer invokes hostt->queuecommand while - holding host_set lock, so all above occur while holding - host_set lock. - - - - - - - - How commands are processed - - Depending on which protocol and which controller are used, - commands are processed differently. For the purpose of - discussion, a controller which uses taskfile interface and all - standard callbacks is assumed. - - - Currently 6 ATA command protocols are used. They can be - sorted into the following four categories according to how - they are processed. - - - - ATA NO DATA or DMA - - - ATA_PROT_NODATA and ATA_PROT_DMA fall into this category. - These types of commands don't require any software - intervention once issued. Device will raise interrupt on - completion. - - - - - ATA PIO - - - ATA_PROT_PIO is in this category. libata currently - implements PIO with polling. ATA_NIEN bit is set to turn - off interrupt and pio_task on ata_wq performs polling and - IO. - - - - - ATAPI NODATA or DMA - - - ATA_PROT_ATAPI_NODATA and ATA_PROT_ATAPI_DMA are in this - category. packet_task is used to poll BSY bit after - issuing PACKET command. Once BSY is turned off by the - device, packet_task transfers CDB and hands off processing - to interrupt handler. - - - - - ATAPI PIO - - - ATA_PROT_ATAPI is in this category. ATA_NIEN bit is set - and, as in ATAPI NODATA or DMA, packet_task submits cdb. - However, after submitting cdb, further processing (data - transfer) is handed off to pio_task. - - - - - - - How commands are completed - - Once issued, all qc's are either completed with - ata_qc_complete() or time out. For commands which are handled - by interrupts, ata_host_intr() invokes ata_qc_complete(), and, - for PIO tasks, pio_task invokes ata_qc_complete(). In error - cases, packet_task may also complete commands. - - - ata_qc_complete() does the following. - - - - - - - DMA memory is unmapped. - - - - - - ATA_QCFLAG_ACTIVE is cleared from qc->flags. - - - - - - qc->complete_fn() callback is invoked. If the return value of - the callback is not zero. Completion is short circuited and - ata_qc_complete() returns. - - - - - - __ata_qc_complete() is called, which does - - - - - qc->flags is cleared to zero. - - - - - - ap->active_tag and qc->tag are poisoned. - - - - - - qc->waiting is cleared & completed (in that order). - - - - - - qc is deallocated by clearing appropriate bit in ap->qactive. - - - - - - - - - - - So, it basically notifies upper layer and deallocates qc. One - exception is short-circuit path in #3 which is used by - atapi_qc_complete(). - - - For all non-ATAPI commands, whether it fails or not, almost - the same code path is taken and very little error handling - takes place. A qc is completed with success status if it - succeeded, with failed status otherwise. - - - However, failed ATAPI commands require more handling as - REQUEST SENSE is needed to acquire sense data. If an ATAPI - command fails, ata_qc_complete() is invoked with error status, - which in turn invokes atapi_qc_complete() via - qc->complete_fn() callback. - - - This makes atapi_qc_complete() set scmd->result to - SAM_STAT_CHECK_CONDITION, complete the scmd and return 1. As - the sense data is empty but scmd->result is CHECK CONDITION, - SCSI midlayer will invoke EH for the scmd, and returning 1 - makes ata_qc_complete() to return without deallocating the qc. - This leads us to ata_scsi_error() with partially completed qc. - - - - - ata_scsi_error() - - ata_scsi_error() is the current transportt->eh_strategy_handler() - for libata. As discussed above, this will be entered in two - cases - timeout and ATAPI error completion. This function - calls low level libata driver's eng_timeout() callback, the - standard callback for which is ata_eng_timeout(). It checks - if a qc is active and calls ata_qc_timeout() on the qc if so. - Actual error handling occurs in ata_qc_timeout(). - - - If EH is invoked for timeout, ata_qc_timeout() stops BMDMA and - completes the qc. Note that as we're currently in EH, we - cannot call scsi_done. As described in SCSI EH doc, a - recovered scmd should be either retried with - scsi_queue_insert() or finished with scsi_finish_command(). - Here, we override qc->scsidone with scsi_finish_command() and - calls ata_qc_complete(). - - - If EH is invoked due to a failed ATAPI qc, the qc here is - completed but not deallocated. The purpose of this - half-completion is to use the qc as place holder to make EH - code reach this place. This is a bit hackish, but it works. - - - Once control reaches here, the qc is deallocated by invoking - __ata_qc_complete() explicitly. Then, internal qc for REQUEST - SENSE is issued. Once sense data is acquired, scmd is - finished by directly invoking scsi_finish_command() on the - scmd. Note that as we already have completed and deallocated - the qc which was associated with the scmd, we don't need - to/cannot call ata_qc_complete() again. - - - - - Problems with the current EH - - - - - - Error representation is too crude. Currently any and all - error conditions are represented with ATA STATUS and ERROR - registers. Errors which aren't ATA device errors are treated - as ATA device errors by setting ATA_ERR bit. Better error - descriptor which can properly represent ATA and other - errors/exceptions is needed. - - - - - - When handling timeouts, no action is taken to make device - forget about the timed out command and ready for new commands. - - - - - - EH handling via ata_scsi_error() is not properly protected - from usual command processing. On EH entrance, the device is - not in quiescent state. Timed out commands may succeed or - fail any time. pio_task and atapi_task may still be running. - - - - - - Too weak error recovery. Devices / controllers causing HSM - mismatch errors and other errors quite often require reset to - return to known state. Also, advanced error handling is - necessary to support features like NCQ and hotplug. - - - - - - ATA errors are directly handled in the interrupt handler and - PIO errors in pio_task. This is problematic for advanced - error handling for the following reasons. - - - First, advanced error handling often requires context and - internal qc execution. - - - Second, even a simple failure (say, CRC error) needs - information gathering and could trigger complex error handling - (say, resetting & reconfiguring). Having multiple code - paths to gather information, enter EH and trigger actions - makes life painful. - - - Third, scattered EH code makes implementing low level drivers - difficult. Low level drivers override libata callbacks. If - EH is scattered over several places, each affected callbacks - should perform its part of error handling. This can be error - prone and painful. - - - - - - - - - libata Library -!Edrivers/ata/libata-core.c - - - - libata Core Internals -!Idrivers/ata/libata-core.c - - - - libata SCSI translation/emulation -!Edrivers/ata/libata-scsi.c -!Idrivers/ata/libata-scsi.c - - - - ATA errors and exceptions - - - This chapter tries to identify what error/exception conditions exist - for ATA/ATAPI devices and describe how they should be handled in - implementation-neutral way. - - - - The term 'error' is used to describe conditions where either an - explicit error condition is reported from device or a command has - timed out. - - - - The term 'exception' is either used to describe exceptional - conditions which are not errors (say, power or hotplug events), or - to describe both errors and non-error exceptional conditions. Where - explicit distinction between error and exception is necessary, the - term 'non-error exception' is used. - - - - Exception categories - - Exceptions are described primarily with respect to legacy - taskfile + bus master IDE interface. If a controller provides - other better mechanism for error reporting, mapping those into - categories described below shouldn't be difficult. - - - - In the following sections, two recovery actions - reset and - reconfiguring transport - are mentioned. These are described - further in . - - - - HSM violation - - This error is indicated when STATUS value doesn't match HSM - requirement during issuing or execution any ATA/ATAPI command. - - - - Examples - - - - ATA_STATUS doesn't contain !BSY && DRDY && !DRQ while trying - to issue a command. - - - - - - !BSY && !DRQ during PIO data transfer. - - - - - - DRQ on command completion. - - - - - - !BSY && ERR after CDB transfer starts but before the - last byte of CDB is transferred. ATA/ATAPI standard states - that "The device shall not terminate the PACKET command - with an error before the last byte of the command packet has - been written" in the error outputs description of PACKET - command and the state diagram doesn't include such - transitions. - - - - - - - In these cases, HSM is violated and not much information - regarding the error can be acquired from STATUS or ERROR - register. IOW, this error can be anything - driver bug, - faulty device, controller and/or cable. - - - - As HSM is violated, reset is necessary to restore known state. - Reconfiguring transport for lower speed might be helpful too - as transmission errors sometimes cause this kind of errors. - - - - - ATA/ATAPI device error (non-NCQ / non-CHECK CONDITION) - - - These are errors detected and reported by ATA/ATAPI devices - indicating device problems. For this type of errors, STATUS - and ERROR register values are valid and describe error - condition. Note that some of ATA bus errors are detected by - ATA/ATAPI devices and reported using the same mechanism as - device errors. Those cases are described later in this - section. - - - - For ATA commands, this type of errors are indicated by !BSY - && ERR during command execution and on completion. - - - For ATAPI commands, - - - - - - !BSY && ERR && ABRT right after issuing PACKET - indicates that PACKET command is not supported and falls in - this category. - - - - - - !BSY && ERR(==CHK) && !ABRT after the last - byte of CDB is transferred indicates CHECK CONDITION and - doesn't fall in this category. - - - - - - !BSY && ERR(==CHK) && ABRT after the last byte - of CDB is transferred *probably* indicates CHECK CONDITION and - doesn't fall in this category. - - - - - - - Of errors detected as above, the following are not ATA/ATAPI - device errors but ATA bus errors and should be handled - according to . - - - - - - CRC error during data transfer - - - This is indicated by ICRC bit in the ERROR register and - means that corruption occurred during data transfer. Up to - ATA/ATAPI-7, the standard specifies that this bit is only - applicable to UDMA transfers but ATA/ATAPI-8 draft revision - 1f says that the bit may be applicable to multiword DMA and - PIO. - - - - - - ABRT error during data transfer or on completion - - - Up to ATA/ATAPI-7, the standard specifies that ABRT could be - set on ICRC errors and on cases where a device is not able - to complete a command. Combined with the fact that MWDMA - and PIO transfer errors aren't allowed to use ICRC bit up to - ATA/ATAPI-7, it seems to imply that ABRT bit alone could - indicate transfer errors. - - - However, ATA/ATAPI-8 draft revision 1f removes the part - that ICRC errors can turn on ABRT. So, this is kind of - gray area. Some heuristics are needed here. - - - - - - - - ATA/ATAPI device errors can be further categorized as follows. - - - - - - Media errors - - - This is indicated by UNC bit in the ERROR register. ATA - devices reports UNC error only after certain number of - retries cannot recover the data, so there's nothing much - else to do other than notifying upper layer. - - - READ and WRITE commands report CHS or LBA of the first - failed sector but ATA/ATAPI standard specifies that the - amount of transferred data on error completion is - indeterminate, so we cannot assume that sectors preceding - the failed sector have been transferred and thus cannot - complete those sectors successfully as SCSI does. - - - - - - Media changed / media change requested error - - - <<TODO: fill here>> - - - - - Address error - - - This is indicated by IDNF bit in the ERROR register. - Report to upper layer. - - - - - Other errors - - - This can be invalid command or parameter indicated by ABRT - ERROR bit or some other error condition. Note that ABRT - bit can indicate a lot of things including ICRC and Address - errors. Heuristics needed. - - - - - - - - Depending on commands, not all STATUS/ERROR bits are - applicable. These non-applicable bits are marked with - "na" in the output descriptions but up to ATA/ATAPI-7 - no definition of "na" can be found. However, - ATA/ATAPI-8 draft revision 1f describes "N/A" as - follows. - - -
- - 3.2.3.3a N/A - - - A keyword the indicates a field has no defined value in - this standard and should not be checked by the host or - device. N/A fields should be cleared to zero. - - - - -
- - - So, it seems reasonable to assume that "na" bits are - cleared to zero by devices and thus need no explicit masking. - - - - - - ATAPI device CHECK CONDITION - - - ATAPI device CHECK CONDITION error is indicated by set CHK bit - (ERR bit) in the STATUS register after the last byte of CDB is - transferred for a PACKET command. For this kind of errors, - sense data should be acquired to gather information regarding - the errors. REQUEST SENSE packet command should be used to - acquire sense data. - - - - Once sense data is acquired, this type of errors can be - handled similarly to other SCSI errors. Note that sense data - may indicate ATA bus error (e.g. Sense Key 04h HARDWARE ERROR - && ASC/ASCQ 47h/00h SCSI PARITY ERROR). In such - cases, the error should be considered as an ATA bus error and - handled according to . - - - - - - ATA device error (NCQ) - - - NCQ command error is indicated by cleared BSY and set ERR bit - during NCQ command phase (one or more NCQ commands - outstanding). Although STATUS and ERROR registers will - contain valid values describing the error, READ LOG EXT is - required to clear the error condition, determine which command - has failed and acquire more information. - - - - READ LOG EXT Log Page 10h reports which tag has failed and - taskfile register values describing the error. With this - information the failed command can be handled as a normal ATA - command error as in and all - other in-flight commands must be retried. Note that this - retry should not be counted - it's likely that commands - retried this way would have completed normally if it were not - for the failed command. - - - - Note that ATA bus errors can be reported as ATA device NCQ - errors. This should be handled as described in . - - - - If READ LOG EXT Log Page 10h fails or reports NQ, we're - thoroughly screwed. This condition should be treated - according to . - - - - - - ATA bus error - - - ATA bus error means that data corruption occurred during - transmission over ATA bus (SATA or PATA). This type of errors - can be indicated by - - - - - - - ICRC or ABRT error as described in . - - - - - - Controller-specific error completion with error information - indicating transmission error. - - - - - - On some controllers, command timeout. In this case, there may - be a mechanism to determine that the timeout is due to - transmission error. - - - - - - Unknown/random errors, timeouts and all sorts of weirdities. - - - - - - - As described above, transmission errors can cause wide variety - of symptoms ranging from device ICRC error to random device - lockup, and, for many cases, there is no way to tell if an - error condition is due to transmission error or not; - therefore, it's necessary to employ some kind of heuristic - when dealing with errors and timeouts. For example, - encountering repetitive ABRT errors for known supported - command is likely to indicate ATA bus error. - - - - Once it's determined that ATA bus errors have possibly - occurred, lowering ATA bus transmission speed is one of - actions which may alleviate the problem. See for more information. - - - - - - PCI bus error - - - Data corruption or other failures during transmission over PCI - (or other system bus). For standard BMDMA, this is indicated - by Error bit in the BMDMA Status register. This type of - errors must be logged as it indicates something is very wrong - with the system. Resetting host controller is recommended. - - - - - - Late completion - - - This occurs when timeout occurs and the timeout handler finds - out that the timed out command has completed successfully or - with error. This is usually caused by lost interrupts. This - type of errors must be logged. Resetting host controller is - recommended. - - - - - - Unknown error (timeout) - - - This is when timeout occurs and the command is still - processing or the host and device are in unknown state. When - this occurs, HSM could be in any valid or invalid state. To - bring the device to known state and make it forget about the - timed out command, resetting is necessary. The timed out - command may be retried. - - - - Timeouts can also be caused by transmission errors. Refer to - for more details. - - - - - - Hotplug and power management exceptions - - - <<TODO: fill here>> - - - - - - - - EH recovery actions - - - This section discusses several important recovery actions. - - - - Clearing error condition - - - Many controllers require its error registers to be cleared by - error handler. Different controllers may have different - requirements. - - - - For SATA, it's strongly recommended to clear at least SError - register during error handling. - - - - - Reset - - - During EH, resetting is necessary in the following cases. - - - - - - - HSM is in unknown or invalid state - - - - - - HBA is in unknown or invalid state - - - - - - EH needs to make HBA/device forget about in-flight commands - - - - - - HBA/device behaves weirdly - - - - - - - Resetting during EH might be a good idea regardless of error - condition to improve EH robustness. Whether to reset both or - either one of HBA and device depends on situation but the - following scheme is recommended. - - - - - - - When it's known that HBA is in ready state but ATA/ATAPI - device is in unknown state, reset only device. - - - - - - If HBA is in unknown state, reset both HBA and device. - - - - - - - HBA resetting is implementation specific. For a controller - complying to taskfile/BMDMA PCI IDE, stopping active DMA - transaction may be sufficient iff BMDMA state is the only HBA - context. But even mostly taskfile/BMDMA PCI IDE complying - controllers may have implementation specific requirements and - mechanism to reset themselves. This must be addressed by - specific drivers. - - - - OTOH, ATA/ATAPI standard describes in detail ways to reset - ATA/ATAPI devices. - - - - - PATA hardware reset - - - This is hardware initiated device reset signalled with - asserted PATA RESET- signal. There is no standard way to - initiate hardware reset from software although some - hardware provides registers that allow driver to directly - tweak the RESET- signal. - - - - - Software reset - - - This is achieved by turning CONTROL SRST bit on for at - least 5us. Both PATA and SATA support it but, in case of - SATA, this may require controller-specific support as the - second Register FIS to clear SRST should be transmitted - while BSY bit is still set. Note that on PATA, this resets - both master and slave devices on a channel. - - - - - EXECUTE DEVICE DIAGNOSTIC command - - - Although ATA/ATAPI standard doesn't describe exactly, EDD - implies some level of resetting, possibly similar level - with software reset. Host-side EDD protocol can be handled - with normal command processing and most SATA controllers - should be able to handle EDD's just like other commands. - As in software reset, EDD affects both devices on a PATA - bus. - - - Although EDD does reset devices, this doesn't suit error - handling as EDD cannot be issued while BSY is set and it's - unclear how it will act when device is in unknown/weird - state. - - - - - ATAPI DEVICE RESET command - - - This is very similar to software reset except that reset - can be restricted to the selected device without affecting - the other device sharing the cable. - - - - - SATA phy reset - - - This is the preferred way of resetting a SATA device. In - effect, it's identical to PATA hardware reset. Note that - this can be done with the standard SCR Control register. - As such, it's usually easier to implement than software - reset. - - - - - - - - One more thing to consider when resetting devices is that - resetting clears certain configuration parameters and they - need to be set to their previous or newly adjusted values - after reset. - - - - Parameters affected are. - - - - - - - CHS set up with INITIALIZE DEVICE PARAMETERS (seldom used) - - - - - - Parameters set with SET FEATURES including transfer mode setting - - - - - - Block count set with SET MULTIPLE MODE - - - - - - Other parameters (SET MAX, MEDIA LOCK...) - - - - - - - ATA/ATAPI standard specifies that some parameters must be - maintained across hardware or software reset, but doesn't - strictly specify all of them. Always reconfiguring needed - parameters after reset is required for robustness. Note that - this also applies when resuming from deep sleep (power-off). - - - - Also, ATA/ATAPI standard requires that IDENTIFY DEVICE / - IDENTIFY PACKET DEVICE is issued after any configuration - parameter is updated or a hardware reset and the result used - for further operation. OS driver is required to implement - revalidation mechanism to support this. - - - - - - Reconfigure transport - - - For both PATA and SATA, a lot of corners are cut for cheap - connectors, cables or controllers and it's quite common to see - high transmission error rate. This can be mitigated by - lowering transmission speed. - - - - The following is a possible scheme Jeff Garzik suggested. - - -
- - If more than $N (3?) transmission errors happen in 15 minutes, - - - - - if SATA, decrease SATA PHY speed. if speed cannot be decreased, - - - - - decrease UDMA xfer speed. if at UDMA0, switch to PIO4, - - - - - decrease PIO xfer speed. if at PIO3, complain, but continue - - - -
- - - - - - - - - ata_piix Internals -!Idrivers/ata/ata_piix.c - - - - sata_sil Internals -!Idrivers/ata/sata_sil.c - - - - Thanks - - The bulk of the ATA knowledge comes thanks to long conversations with - Andre Hedrick (www.linux-ide.org), and long hours pondering the ATA - and SCSI specifications. - - - Thanks to Alan Cox for pointing out similarities - between SATA and SCSI, and in general for motivation to hack on - libata. - - - libata's device detection - method, ata_pio_devchk, and in general all the early probing was - based on extensive study of Hale Landis's probe/reset code in his - ATADRVR driver (www.ata-atapi.com). - - - - diff --git a/Documentation/driver-api/index.rst b/Documentation/driver-api/index.rst index 8058a87..c3c50b1 100644 --- a/Documentation/driver-api/index.rst +++ b/Documentation/driver-api/index.rst @@ -32,6 +32,7 @@ available subsections can be seen below. i2c hsi edac + libata miscellaneous vme 80211/index diff --git a/Documentation/driver-api/libata.rst b/Documentation/driver-api/libata.rst new file mode 100644 index 0000000..774bf23 --- /dev/null +++ b/Documentation/driver-api/libata.rst @@ -0,0 +1,1027 @@ +======================== +libATA Developer's Guide +======================== + +:Author: Jeff Garzik + +Introduction +============ + +libATA is a library used inside the Linux kernel to support ATA host +controllers and devices. libATA provides an ATA driver API, class +transports for ATA and ATAPI devices, and SCSI<->ATA translation for ATA +devices according to the T10 SAT specification. + +This Guide documents the libATA driver API, library functions, library +internals, and a couple sample ATA low-level drivers. + +libata Driver API +================= + +struct ata_port_operations is defined for every low-level libata +hardware driver, and it controls how the low-level driver interfaces +with the ATA and SCSI layers. + +FIS-based drivers will hook into the system with ->qc_prep() and +->qc_issue() high-level hooks. Hardware which behaves in a manner +similar to PCI IDE hardware may utilize several generic helpers, +defining at a bare minimum the bus I/O addresses of the ATA shadow +register blocks. + +struct ata_port_operations +---------------------------- + +Disable ATA port +~~~~~~~~~~~~~~~~ + +:: + + void (*port_disable) (struct ata_port *); + + +Called from ata_bus_probe() error path, as well as when unregistering +from the SCSI module (rmmod, hot unplug). This function should do +whatever needs to be done to take the port out of use. In most cases, +ata_port_disable() can be used as this hook. + +Called from ata_bus_probe() on a failed probe. Called from +ata_scsi_release(). + +Post-IDENTIFY device configuration +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +:: + + void (*dev_config) (struct ata_port *, struct ata_device *); + + +Called after IDENTIFY [PACKET] DEVICE is issued to each device found. +Typically used to apply device-specific fixups prior to issue of SET +FEATURES - XFER MODE, and prior to operation. + +This entry may be specified as NULL in ata_port_operations. + +Set PIO/DMA mode +~~~~~~~~~~~~~~~~ + +:: + + void (*set_piomode) (struct ata_port *, struct ata_device *); + void (*set_dmamode) (struct ata_port *, struct ata_device *); + void (*post_set_mode) (struct ata_port *); + unsigned int (*mode_filter) (struct ata_port *, struct ata_device *, unsigned int); + + +Hooks called prior to the issue of SET FEATURES - XFER MODE command. The +optional ->mode_filter() hook is called when libata has built a mask of +the possible modes. This is passed to the ->mode_filter() function +which should return a mask of valid modes after filtering those +unsuitable due to hardware limits. It is not valid to use this interface +to add modes. + +dev->pio_mode and dev->dma_mode are guaranteed to be valid when +->set_piomode() and when ->set_dmamode() is called. The timings for +any other drive sharing the cable will also be valid at this point. That +is the library records the decisions for the modes of each drive on a +channel before it attempts to set any of them. + +->post_set_mode() is called unconditionally, after the SET FEATURES - +XFER MODE command completes successfully. + +->set_piomode() is always called (if present), but ->set_dma_mode() +is only called if DMA is possible. + +Taskfile read/write +~~~~~~~~~~~~~~~~~~~ + +:: + + void (*sff_tf_load) (struct ata_port *ap, struct ata_taskfile *tf); + void (*sff_tf_read) (struct ata_port *ap, struct ata_taskfile *tf); + + +->tf_load() is called to load the given taskfile into hardware +registers / DMA buffers. ->tf_read() is called to read the hardware +registers / DMA buffers, to obtain the current set of taskfile register +values. Most drivers for taskfile-based hardware (PIO or MMIO) use +ata_sff_tf_load() and ata_sff_tf_read() for these hooks. + +PIO data read/write +~~~~~~~~~~~~~~~~~~~ + +:: + + void (*sff_data_xfer) (struct ata_device *, unsigned char *, unsigned int, int); + + +All bmdma-style drivers must implement this hook. This is the low-level +operation that actually copies the data bytes during a PIO data +transfer. Typically the driver will choose one of +ata_sff_data_xfer_noirq(), ata_sff_data_xfer(), or +ata_sff_data_xfer32(). + +ATA command execute +~~~~~~~~~~~~~~~~~~~ + +:: + + void (*sff_exec_command)(struct ata_port *ap, struct ata_taskfile *tf); + + +causes an ATA command, previously loaded with ->tf_load(), to be +initiated in hardware. Most drivers for taskfile-based hardware use +ata_sff_exec_command() for this hook. + +Per-cmd ATAPI DMA capabilities filter +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +:: + + int (*check_atapi_dma) (struct ata_queued_cmd *qc); + + +Allow low-level driver to filter ATA PACKET commands, returning a status +indicating whether or not it is OK to use DMA for the supplied PACKET +command. + +This hook may be specified as NULL, in which case libata will assume +that atapi dma can be supported. + +Read specific ATA shadow registers +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +:: + + u8 (*sff_check_status)(struct ata_port *ap); + u8 (*sff_check_altstatus)(struct ata_port *ap); + + +Reads the Status/AltStatus ATA shadow register from hardware. On some +hardware, reading the Status register has the side effect of clearing +the interrupt condition. Most drivers for taskfile-based hardware use +ata_sff_check_status() for this hook. + +Write specific ATA shadow register +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +:: + + void (*sff_set_devctl)(struct ata_port *ap, u8 ctl); + + +Write the device control ATA shadow register to the hardware. Most +drivers don't need to define this. + +Select ATA device on bus +~~~~~~~~~~~~~~~~~~~~~~~~ + +:: + + void (*sff_dev_select)(struct ata_port *ap, unsigned int device); + + +Issues the low-level hardware command(s) that causes one of N hardware +devices to be considered 'selected' (active and available for use) on +the ATA bus. This generally has no meaning on FIS-based devices. + +Most drivers for taskfile-based hardware use ata_sff_dev_select() for +this hook. + +Private tuning method +~~~~~~~~~~~~~~~~~~~~~ + +:: + + void (*set_mode) (struct ata_port *ap); + + +By default libata performs drive and controller tuning in accordance +with the ATA timing rules and also applies blacklists and cable limits. +Some controllers need special handling and have custom tuning rules, +typically raid controllers that use ATA commands but do not actually do +drive timing. + + **Warning** + + This hook should not be used to replace the standard controller + tuning logic when a controller has quirks. Replacing the default + tuning logic in that case would bypass handling for drive and bridge + quirks that may be important to data reliability. If a controller + needs to filter the mode selection it should use the mode_filter + hook instead. + +Control PCI IDE BMDMA engine +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +:: + + void (*bmdma_setup) (struct ata_queued_cmd *qc); + void (*bmdma_start) (struct ata_queued_cmd *qc); + void (*bmdma_stop) (struct ata_port *ap); + u8 (*bmdma_status) (struct ata_port *ap); + + +When setting up an IDE BMDMA transaction, these hooks arm +(->bmdma_setup), fire (->bmdma_start), and halt (->bmdma_stop) the +hardware's DMA engine. ->bmdma_status is used to read the standard PCI +IDE DMA Status register. + +These hooks are typically either no-ops, or simply not implemented, in +FIS-based drivers. + +Most legacy IDE drivers use ata_bmdma_setup() for the bmdma_setup() +hook. ata_bmdma_setup() will write the pointer to the PRD table to the +IDE PRD Table Address register, enable DMA in the DMA Command register, +and call exec_command() to begin the transfer. + +Most legacy IDE drivers use ata_bmdma_start() for the bmdma_start() +hook. ata_bmdma_start() will write the ATA_DMA_START flag to the DMA +Command register. + +Many legacy IDE drivers use ata_bmdma_stop() for the bmdma_stop() +hook. ata_bmdma_stop() clears the ATA_DMA_START flag in the DMA +command register. + +Many legacy IDE drivers use ata_bmdma_status() as the bmdma_status() +hook. + +High-level taskfile hooks +~~~~~~~~~~~~~~~~~~~~~~~~~ + +:: + + void (*qc_prep) (struct ata_queued_cmd *qc); + int (*qc_issue) (struct ata_queued_cmd *qc); + + +Higher-level hooks, these two hooks can potentially supercede several of +the above taskfile/DMA engine hooks. ->qc_prep is called after the +buffers have been DMA-mapped, and is typically used to populate the +hardware's DMA scatter-gather table. Most drivers use the standard +ata_qc_prep() helper function, but more advanced drivers roll their +own. + +->qc_issue is used to make a command active, once the hardware and S/G +tables have been prepared. IDE BMDMA drivers use the helper function +ata_qc_issue_prot() for taskfile protocol-based dispatch. More +advanced drivers implement their own ->qc_issue. + +ata_qc_issue_prot() calls ->tf_load(), ->bmdma_setup(), and +->bmdma_start() as necessary to initiate a transfer. + +Exception and probe handling (EH) +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +:: + + void (*eng_timeout) (struct ata_port *ap); + void (*phy_reset) (struct ata_port *ap); + + +Deprecated. Use ->error_handler() instead. + +:: + + void (*freeze) (struct ata_port *ap); + void (*thaw) (struct ata_port *ap); + + +ata_port_freeze() is called when HSM violations or some other +condition disrupts normal operation of the port. A frozen port is not +allowed to perform any operation until the port is thawed, which usually +follows a successful reset. + +The optional ->freeze() callback can be used for freezing the port +hardware-wise (e.g. mask interrupt and stop DMA engine). If a port +cannot be frozen hardware-wise, the interrupt handler must ack and clear +interrupts unconditionally while the port is frozen. + +The optional ->thaw() callback is called to perform the opposite of +->freeze(): prepare the port for normal operation once again. Unmask +interrupts, start DMA engine, etc. + +:: + + void (*error_handler) (struct ata_port *ap); + + +->error_handler() is a driver's hook into probe, hotplug, and recovery +and other exceptional conditions. The primary responsibility of an +implementation is to call ata_do_eh() or ata_bmdma_drive_eh() with +a set of EH hooks as arguments: + +'prereset' hook (may be NULL) is called during an EH reset, before any +other actions are taken. + +'postreset' hook (may be NULL) is called after the EH reset is +performed. Based on existing conditions, severity of the problem, and +hardware capabilities, + +Either 'softreset' (may be NULL) or 'hardreset' (may be NULL) will be +called to perform the low-level EH reset. + +:: + + void (*post_internal_cmd) (struct ata_queued_cmd *qc); + + +Perform any hardware-specific actions necessary to finish processing +after executing a probe-time or EH-time command via +ata_exec_internal(). + +Hardware interrupt handling +~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +:: + + irqreturn_t (*irq_handler)(int, void *, struct pt_regs *); + void (*irq_clear) (struct ata_port *); + + +->irq_handler is the interrupt handling routine registered with the +system, by libata. ->irq_clear is called during probe just before the +interrupt handler is registered, to be sure hardware is quiet. + +The second argument, dev_instance, should be cast to a pointer to +struct ata_host_set. + +Most legacy IDE drivers use ata_sff_interrupt() for the irq_handler +hook, which scans all ports in the host_set, determines which queued +command was active (if any), and calls ata_sff_host_intr(ap,qc). + +Most legacy IDE drivers use ata_sff_irq_clear() for the irq_clear() +hook, which simply clears the interrupt and error flags in the DMA +status register. + +SATA phy read/write +~~~~~~~~~~~~~~~~~~~ + +:: + + int (*scr_read) (struct ata_port *ap, unsigned int sc_reg, + u32 *val); + int (*scr_write) (struct ata_port *ap, unsigned int sc_reg, + u32 val); + + +Read and write standard SATA phy registers. Currently only used if +->phy_reset hook called the sata_phy_reset() helper function. sc_reg +is one of SCR_STATUS, SCR_CONTROL, SCR_ERROR, or SCR_ACTIVE. + +Init and shutdown +~~~~~~~~~~~~~~~~~ + +:: + + int (*port_start) (struct ata_port *ap); + void (*port_stop) (struct ata_port *ap); + void (*host_stop) (struct ata_host_set *host_set); + + +->port_start() is called just after the data structures for each port +are initialized. Typically this is used to alloc per-port DMA buffers / +tables / rings, enable DMA engines, and similar tasks. Some drivers also +use this entry point as a chance to allocate driver-private memory for +ap->private_data. + +Many drivers use ata_port_start() as this hook or call it from their +own port_start() hooks. ata_port_start() allocates space for a legacy +IDE PRD table and returns. + +->port_stop() is called after ->host_stop(). Its sole function is to +release DMA/memory resources, now that they are no longer actively being +used. Many drivers also free driver-private data from port at this time. + +->host_stop() is called after all ->port_stop() calls have completed. +The hook must finalize hardware shutdown, release DMA and other +resources, etc. This hook may be specified as NULL, in which case it is +not called. + +Error handling +============== + +This chapter describes how errors are handled under libata. Readers are +advised to read SCSI EH (Documentation/scsi/scsi_eh.txt) and ATA +exceptions doc first. + +Origins of commands +------------------- + +In libata, a command is represented with struct ata_queued_cmd or qc. +qc's are preallocated during port initialization and repetitively used +for command executions. Currently only one qc is allocated per port but +yet-to-be-merged NCQ branch allocates one for each tag and maps each qc +to NCQ tag 1-to-1. + +libata commands can originate from two sources - libata itself and SCSI +midlayer. libata internal commands are used for initialization and error +handling. All normal blk requests and commands for SCSI emulation are +passed as SCSI commands through queuecommand callback of SCSI host +template. + +How commands are issued +----------------------- + +Internal commands + First, qc is allocated and initialized using ata_qc_new_init(). + Although ata_qc_new_init() doesn't implement any wait or retry + mechanism when qc is not available, internal commands are currently + issued only during initialization and error recovery, so no other + command is active and allocation is guaranteed to succeed. + + Once allocated qc's taskfile is initialized for the command to be + executed. qc currently has two mechanisms to notify completion. One + is via qc->complete_fn() callback and the other is completion + qc->waiting. qc->complete_fn() callback is the asynchronous path + used by normal SCSI translated commands and qc->waiting is the + synchronous (issuer sleeps in process context) path used by internal + commands. + + Once initialization is complete, host_set lock is acquired and the + qc is issued. + +SCSI commands + All libata drivers use ata_scsi_queuecmd() as hostt->queuecommand + callback. scmds can either be simulated or translated. No qc is + involved in processing a simulated scmd. The result is computed + right away and the scmd is completed. + + For a translated scmd, ata_qc_new_init() is invoked to allocate a + qc and the scmd is translated into the qc. SCSI midlayer's + completion notification function pointer is stored into + qc->scsidone. + + qc->complete_fn() callback is used for completion notification. ATA + commands use ata_scsi_qc_complete() while ATAPI commands use + atapi_qc_complete(). Both functions end up calling qc->scsidone to + notify upper layer when the qc is finished. After translation is + completed, the qc is issued with ata_qc_issue(). + + Note that SCSI midlayer invokes hostt->queuecommand while holding + host_set lock, so all above occur while holding host_set lock. + +How commands are processed +-------------------------- + +Depending on which protocol and which controller are used, commands are +processed differently. For the purpose of discussion, a controller which +uses taskfile interface and all standard callbacks is assumed. + +Currently 6 ATA command protocols are used. They can be sorted into the +following four categories according to how they are processed. + +ATA NO DATA or DMA + ATA_PROT_NODATA and ATA_PROT_DMA fall into this category. These + types of commands don't require any software intervention once + issued. Device will raise interrupt on completion. + +ATA PIO + ATA_PROT_PIO is in this category. libata currently implements PIO + with polling. ATA_NIEN bit is set to turn off interrupt and + pio_task on ata_wq performs polling and IO. + +ATAPI NODATA or DMA + ATA_PROT_ATAPI_NODATA and ATA_PROT_ATAPI_DMA are in this + category. packet_task is used to poll BSY bit after issuing PACKET + command. Once BSY is turned off by the device, packet_task + transfers CDB and hands off processing to interrupt handler. + +ATAPI PIO + ATA_PROT_ATAPI is in this category. ATA_NIEN bit is set and, as + in ATAPI NODATA or DMA, packet_task submits cdb. However, after + submitting cdb, further processing (data transfer) is handed off to + pio_task. + +How commands are completed +-------------------------- + +Once issued, all qc's are either completed with ata_qc_complete() or +time out. For commands which are handled by interrupts, +ata_host_intr() invokes ata_qc_complete(), and, for PIO tasks, +pio_task invokes ata_qc_complete(). In error cases, packet_task may +also complete commands. + +ata_qc_complete() does the following. + +1. DMA memory is unmapped. + +2. ATA_QCFLAG_ACTIVE is cleared from qc->flags. + +3. qc->complete_fn() callback is invoked. If the return value of the + callback is not zero. Completion is short circuited and + ata_qc_complete() returns. + +4. __ata_qc_complete() is called, which does + + 1. qc->flags is cleared to zero. + + 2. ap->active_tag and qc->tag are poisoned. + + 3. qc->waiting is cleared & completed (in that order). + + 4. qc is deallocated by clearing appropriate bit in ap->qactive. + +So, it basically notifies upper layer and deallocates qc. One exception +is short-circuit path in #3 which is used by atapi_qc_complete(). + +For all non-ATAPI commands, whether it fails or not, almost the same +code path is taken and very little error handling takes place. A qc is +completed with success status if it succeeded, with failed status +otherwise. + +However, failed ATAPI commands require more handling as REQUEST SENSE is +needed to acquire sense data. If an ATAPI command fails, +ata_qc_complete() is invoked with error status, which in turn invokes +atapi_qc_complete() via qc->complete_fn() callback. + +This makes atapi_qc_complete() set scmd->result to +SAM_STAT_CHECK_CONDITION, complete the scmd and return 1. As the +sense data is empty but scmd->result is CHECK CONDITION, SCSI midlayer +will invoke EH for the scmd, and returning 1 makes ata_qc_complete() +to return without deallocating the qc. This leads us to +ata_scsi_error() with partially completed qc. + +ata_scsi_error() +------------------ + +ata_scsi_error() is the current transportt->eh_strategy_handler() +for libata. As discussed above, this will be entered in two cases - +timeout and ATAPI error completion. This function calls low level libata +driver's eng_timeout() callback, the standard callback for which is +ata_eng_timeout(). It checks if a qc is active and calls +ata_qc_timeout() on the qc if so. Actual error handling occurs in +ata_qc_timeout(). + +If EH is invoked for timeout, ata_qc_timeout() stops BMDMA and +completes the qc. Note that as we're currently in EH, we cannot call +scsi_done. As described in SCSI EH doc, a recovered scmd should be +either retried with scsi_queue_insert() or finished with +scsi_finish_command(). Here, we override qc->scsidone with +scsi_finish_command() and calls ata_qc_complete(). + +If EH is invoked due to a failed ATAPI qc, the qc here is completed but +not deallocated. The purpose of this half-completion is to use the qc as +place holder to make EH code reach this place. This is a bit hackish, +but it works. + +Once control reaches here, the qc is deallocated by invoking +__ata_qc_complete() explicitly. Then, internal qc for REQUEST SENSE +is issued. Once sense data is acquired, scmd is finished by directly +invoking scsi_finish_command() on the scmd. Note that as we already +have completed and deallocated the qc which was associated with the +scmd, we don't need to/cannot call ata_qc_complete() again. + +Problems with the current EH +---------------------------- + +- Error representation is too crude. Currently any and all error + conditions are represented with ATA STATUS and ERROR registers. + Errors which aren't ATA device errors are treated as ATA device + errors by setting ATA_ERR bit. Better error descriptor which can + properly represent ATA and other errors/exceptions is needed. + +- When handling timeouts, no action is taken to make device forget + about the timed out command and ready for new commands. + +- EH handling via ata_scsi_error() is not properly protected from + usual command processing. On EH entrance, the device is not in + quiescent state. Timed out commands may succeed or fail any time. + pio_task and atapi_task may still be running. + +- Too weak error recovery. Devices / controllers causing HSM mismatch + errors and other errors quite often require reset to return to known + state. Also, advanced error handling is necessary to support features + like NCQ and hotplug. + +- ATA errors are directly handled in the interrupt handler and PIO + errors in pio_task. This is problematic for advanced error handling + for the following reasons. + + First, advanced error handling often requires context and internal qc + execution. + + Second, even a simple failure (say, CRC error) needs information + gathering and could trigger complex error handling (say, resetting & + reconfiguring). Having multiple code paths to gather information, + enter EH and trigger actions makes life painful. + + Third, scattered EH code makes implementing low level drivers + difficult. Low level drivers override libata callbacks. If EH is + scattered over several places, each affected callbacks should perform + its part of error handling. This can be error prone and painful. + +libata Library +============== + +.. kernel-doc:: drivers/ata/libata-core.c + :export: + +libata Core Internals +===================== + +.. kernel-doc:: drivers/ata/libata-core.c + :internal: + +libata SCSI translation/emulation +================================= + +.. kernel-doc:: drivers/ata/libata-scsi.c + :export: + +.. kernel-doc:: drivers/ata/libata-scsi.c + :internal: + +ATA errors and exceptions +========================= + +This chapter tries to identify what error/exception conditions exist for +ATA/ATAPI devices and describe how they should be handled in +implementation-neutral way. + +The term 'error' is used to describe conditions where either an explicit +error condition is reported from device or a command has timed out. + +The term 'exception' is either used to describe exceptional conditions +which are not errors (say, power or hotplug events), or to describe both +errors and non-error exceptional conditions. Where explicit distinction +between error and exception is necessary, the term 'non-error exception' +is used. + +Exception categories +-------------------- + +Exceptions are described primarily with respect to legacy taskfile + bus +master IDE interface. If a controller provides other better mechanism +for error reporting, mapping those into categories described below +shouldn't be difficult. + +In the following sections, two recovery actions - reset and +reconfiguring transport - are mentioned. These are described further in +`EH recovery actions <#exrec>`__. + +HSM violation +~~~~~~~~~~~~~ + +This error is indicated when STATUS value doesn't match HSM requirement +during issuing or execution any ATA/ATAPI command. + +- ATA_STATUS doesn't contain !BSY && DRDY && !DRQ while trying to + issue a command. + +- !BSY && !DRQ during PIO data transfer. + +- DRQ on command completion. + +- !BSY && ERR after CDB transfer starts but before the last byte of CDB + is transferred. ATA/ATAPI standard states that "The device shall not + terminate the PACKET command with an error before the last byte of + the command packet has been written" in the error outputs description + of PACKET command and the state diagram doesn't include such + transitions. + +In these cases, HSM is violated and not much information regarding the +error can be acquired from STATUS or ERROR register. IOW, this error can +be anything - driver bug, faulty device, controller and/or cable. + +As HSM is violated, reset is necessary to restore known state. +Reconfiguring transport for lower speed might be helpful too as +transmission errors sometimes cause this kind of errors. + +ATA/ATAPI device error (non-NCQ / non-CHECK CONDITION) +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +These are errors detected and reported by ATA/ATAPI devices indicating +device problems. For this type of errors, STATUS and ERROR register +values are valid and describe error condition. Note that some of ATA bus +errors are detected by ATA/ATAPI devices and reported using the same +mechanism as device errors. Those cases are described later in this +section. + +For ATA commands, this type of errors are indicated by !BSY && ERR +during command execution and on completion. + +For ATAPI commands, + +- !BSY && ERR && ABRT right after issuing PACKET indicates that PACKET + command is not supported and falls in this category. + +- !BSY && ERR(==CHK) && !ABRT after the last byte of CDB is transferred + indicates CHECK CONDITION and doesn't fall in this category. + +- !BSY && ERR(==CHK) && ABRT after the last byte of CDB is transferred + \*probably\* indicates CHECK CONDITION and doesn't fall in this + category. + +Of errors detected as above, the following are not ATA/ATAPI device +errors but ATA bus errors and should be handled according to +`ATA bus error <#excatATAbusErr>`__. + +CRC error during data transfer + This is indicated by ICRC bit in the ERROR register and means that + corruption occurred during data transfer. Up to ATA/ATAPI-7, the + standard specifies that this bit is only applicable to UDMA + transfers but ATA/ATAPI-8 draft revision 1f says that the bit may be + applicable to multiword DMA and PIO. + +ABRT error during data transfer or on completion + Up to ATA/ATAPI-7, the standard specifies that ABRT could be set on + ICRC errors and on cases where a device is not able to complete a + command. Combined with the fact that MWDMA and PIO transfer errors + aren't allowed to use ICRC bit up to ATA/ATAPI-7, it seems to imply + that ABRT bit alone could indicate transfer errors. + + However, ATA/ATAPI-8 draft revision 1f removes the part that ICRC + errors can turn on ABRT. So, this is kind of gray area. Some + heuristics are needed here. + +ATA/ATAPI device errors can be further categorized as follows. + +Media errors + This is indicated by UNC bit in the ERROR register. ATA devices + reports UNC error only after certain number of retries cannot + recover the data, so there's nothing much else to do other than + notifying upper layer. + + READ and WRITE commands report CHS or LBA of the first failed sector + but ATA/ATAPI standard specifies that the amount of transferred data + on error completion is indeterminate, so we cannot assume that + sectors preceding the failed sector have been transferred and thus + cannot complete those sectors successfully as SCSI does. + +Media changed / media change requested error + <> + +Address error + This is indicated by IDNF bit in the ERROR register. Report to upper + layer. + +Other errors + This can be invalid command or parameter indicated by ABRT ERROR bit + or some other error condition. Note that ABRT bit can indicate a lot + of things including ICRC and Address errors. Heuristics needed. + +Depending on commands, not all STATUS/ERROR bits are applicable. These +non-applicable bits are marked with "na" in the output descriptions but +up to ATA/ATAPI-7 no definition of "na" can be found. However, +ATA/ATAPI-8 draft revision 1f describes "N/A" as follows. + + 3.2.3.3a N/A + A keyword the indicates a field has no defined value in this + standard and should not be checked by the host or device. N/A + fields should be cleared to zero. + +So, it seems reasonable to assume that "na" bits are cleared to zero by +devices and thus need no explicit masking. + +ATAPI device CHECK CONDITION +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +ATAPI device CHECK CONDITION error is indicated by set CHK bit (ERR bit) +in the STATUS register after the last byte of CDB is transferred for a +PACKET command. For this kind of errors, sense data should be acquired +to gather information regarding the errors. REQUEST SENSE packet command +should be used to acquire sense data. + +Once sense data is acquired, this type of errors can be handled +similarly to other SCSI errors. Note that sense data may indicate ATA +bus error (e.g. Sense Key 04h HARDWARE ERROR && ASC/ASCQ 47h/00h SCSI +PARITY ERROR). In such cases, the error should be considered as an ATA +bus error and handled according to `ATA bus error <#excatATAbusErr>`__. + +ATA device error (NCQ) +~~~~~~~~~~~~~~~~~~~~~~ + +NCQ command error is indicated by cleared BSY and set ERR bit during NCQ +command phase (one or more NCQ commands outstanding). Although STATUS +and ERROR registers will contain valid values describing the error, READ +LOG EXT is required to clear the error condition, determine which +command has failed and acquire more information. + +READ LOG EXT Log Page 10h reports which tag has failed and taskfile +register values describing the error. With this information the failed +command can be handled as a normal ATA command error as in +`ATA/ATAPI device error (non-NCQ / non-CHECK CONDITION) <#excatDevErr>`__ +and all other in-flight commands must be retried. Note that this retry +should not be counted - it's likely that commands retried this way would +have completed normally if it were not for the failed command. + +Note that ATA bus errors can be reported as ATA device NCQ errors. This +should be handled as described in `ATA bus error <#excatATAbusErr>`__. + +If READ LOG EXT Log Page 10h fails or reports NQ, we're thoroughly +screwed. This condition should be treated according to +`HSM violation <#excatHSMviolation>`__. + +ATA bus error +~~~~~~~~~~~~~ + +ATA bus error means that data corruption occurred during transmission +over ATA bus (SATA or PATA). This type of errors can be indicated by + +- ICRC or ABRT error as described in + `ATA/ATAPI device error (non-NCQ / non-CHECK CONDITION) <#excatDevErr>`__. + +- Controller-specific error completion with error information + indicating transmission error. + +- On some controllers, command timeout. In this case, there may be a + mechanism to determine that the timeout is due to transmission error. + +- Unknown/random errors, timeouts and all sorts of weirdities. + +As described above, transmission errors can cause wide variety of +symptoms ranging from device ICRC error to random device lockup, and, +for many cases, there is no way to tell if an error condition is due to +transmission error or not; therefore, it's necessary to employ some kind +of heuristic when dealing with errors and timeouts. For example, +encountering repetitive ABRT errors for known supported command is +likely to indicate ATA bus error. + +Once it's determined that ATA bus errors have possibly occurred, +lowering ATA bus transmission speed is one of actions which may +alleviate the problem. See `Reconfigure transport <#exrecReconf>`__ for +more information. + +PCI bus error +~~~~~~~~~~~~~ + +Data corruption or other failures during transmission over PCI (or other +system bus). For standard BMDMA, this is indicated by Error bit in the +BMDMA Status register. This type of errors must be logged as it +indicates something is very wrong with the system. Resetting host +controller is recommended. + +Late completion +~~~~~~~~~~~~~~~ + +This occurs when timeout occurs and the timeout handler finds out that +the timed out command has completed successfully or with error. This is +usually caused by lost interrupts. This type of errors must be logged. +Resetting host controller is recommended. + +Unknown error (timeout) +~~~~~~~~~~~~~~~~~~~~~~~ + +This is when timeout occurs and the command is still processing or the +host and device are in unknown state. When this occurs, HSM could be in +any valid or invalid state. To bring the device to known state and make +it forget about the timed out command, resetting is necessary. The timed +out command may be retried. + +Timeouts can also be caused by transmission errors. Refer to +`ATA bus error <#excatATAbusErr>`__ for more details. + +Hotplug and power management exceptions +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +<> + +EH recovery actions +------------------- + +This section discusses several important recovery actions. + +Clearing error condition +~~~~~~~~~~~~~~~~~~~~~~~~ + +Many controllers require its error registers to be cleared by error +handler. Different controllers may have different requirements. + +For SATA, it's strongly recommended to clear at least SError register +during error handling. + +Reset +~~~~~ + +During EH, resetting is necessary in the following cases. + +- HSM is in unknown or invalid state + +- HBA is in unknown or invalid state + +- EH needs to make HBA/device forget about in-flight commands + +- HBA/device behaves weirdly + +Resetting during EH might be a good idea regardless of error condition +to improve EH robustness. Whether to reset both or either one of HBA and +device depends on situation but the following scheme is recommended. + +- When it's known that HBA is in ready state but ATA/ATAPI device is in + unknown state, reset only device. + +- If HBA is in unknown state, reset both HBA and device. + +HBA resetting is implementation specific. For a controller complying to +taskfile/BMDMA PCI IDE, stopping active DMA transaction may be +sufficient iff BMDMA state is the only HBA context. But even mostly +taskfile/BMDMA PCI IDE complying controllers may have implementation +specific requirements and mechanism to reset themselves. This must be +addressed by specific drivers. + +OTOH, ATA/ATAPI standard describes in detail ways to reset ATA/ATAPI +devices. + +PATA hardware reset + This is hardware initiated device reset signalled with asserted PATA + RESET- signal. There is no standard way to initiate hardware reset + from software although some hardware provides registers that allow + driver to directly tweak the RESET- signal. + +Software reset + This is achieved by turning CONTROL SRST bit on for at least 5us. + Both PATA and SATA support it but, in case of SATA, this may require + controller-specific support as the second Register FIS to clear SRST + should be transmitted while BSY bit is still set. Note that on PATA, + this resets both master and slave devices on a channel. + +EXECUTE DEVICE DIAGNOSTIC command + Although ATA/ATAPI standard doesn't describe exactly, EDD implies + some level of resetting, possibly similar level with software reset. + Host-side EDD protocol can be handled with normal command processing + and most SATA controllers should be able to handle EDD's just like + other commands. As in software reset, EDD affects both devices on a + PATA bus. + + Although EDD does reset devices, this doesn't suit error handling as + EDD cannot be issued while BSY is set and it's unclear how it will + act when device is in unknown/weird state. + +ATAPI DEVICE RESET command + This is very similar to software reset except that reset can be + restricted to the selected device without affecting the other device + sharing the cable. + +SATA phy reset + This is the preferred way of resetting a SATA device. In effect, + it's identical to PATA hardware reset. Note that this can be done + with the standard SCR Control register. As such, it's usually easier + to implement than software reset. + +One more thing to consider when resetting devices is that resetting +clears certain configuration parameters and they need to be set to their +previous or newly adjusted values after reset. + +Parameters affected are. + +- CHS set up with INITIALIZE DEVICE PARAMETERS (seldom used) + +- Parameters set with SET FEATURES including transfer mode setting + +- Block count set with SET MULTIPLE MODE + +- Other parameters (SET MAX, MEDIA LOCK...) + +ATA/ATAPI standard specifies that some parameters must be maintained +across hardware or software reset, but doesn't strictly specify all of +them. Always reconfiguring needed parameters after reset is required for +robustness. Note that this also applies when resuming from deep sleep +(power-off). + +Also, ATA/ATAPI standard requires that IDENTIFY DEVICE / IDENTIFY PACKET +DEVICE is issued after any configuration parameter is updated or a +hardware reset and the result used for further operation. OS driver is +required to implement revalidation mechanism to support this. + +Reconfigure transport +~~~~~~~~~~~~~~~~~~~~~ + +For both PATA and SATA, a lot of corners are cut for cheap connectors, +cables or controllers and it's quite common to see high transmission +error rate. This can be mitigated by lowering transmission speed. + +The following is a possible scheme Jeff Garzik suggested. + + If more than $N (3?) transmission errors happen in 15 minutes, + + - if SATA, decrease SATA PHY speed. if speed cannot be decreased, + + - decrease UDMA xfer speed. if at UDMA0, switch to PIO4, + + - decrease PIO xfer speed. if at PIO3, complain, but continue + +ata_piix Internals +=================== + +.. kernel-doc:: drivers/ata/ata_piix.c + :internal: + +sata_sil Internals +=================== + +.. kernel-doc:: drivers/ata/sata_sil.c + :internal: + +Thanks +====== + +The bulk of the ATA knowledge comes thanks to long conversations with +Andre Hedrick (www.linux-ide.org), and long hours pondering the ATA and +SCSI specifications. + +Thanks to Alan Cox for pointing out similarities between SATA and SCSI, +and in general for motivation to hack on libata. + +libata's device detection method, ata_pio_devchk, and in general all +the early probing was based on extensive study of Hale Landis's +probe/reset code in his ATADRVR driver (www.ata-atapi.com). -- 2.7.4