--- /dev/null
+.. SPDX-License-Identifier: GPL-2.0
+
+=================
+PCI NTB Function
+=================
+
+:Author: Kishon Vijay Abraham I <kishon@ti.com>
+
+PCI Non-Transparent Bridges (NTB) allow two host systems to communicate
+with each other by exposing each host as a device to the other host.
+NTBs typically support the ability to generate interrupts on the remote
+machine, expose memory ranges as BARs, and perform DMA. They also support
+scratchpads, which are areas of memory within the NTB that are accessible
+from both machines.
+
+PCI NTB Function allows two different systems (or hosts) to communicate
+with each other by configuring the endpoint instances in such a way that
+transactions from one system are routed to the other system.
+
+In the below diagram, PCI NTB function configures the SoC with multiple
+PCI Endpoint (EP) instances in such a way that transactions from one EP
+controller are routed to the other EP controller. Once PCI NTB function
+configures the SoC with multiple EP instances, HOST1 and HOST2 can
+communicate with each other using SoC as a bridge.
+
+.. code-block:: text
+
+ +-------------+ +-------------+
+ | | | |
+ | HOST1 | | HOST2 |
+ | | | |
+ +------^------+ +------^------+
+ | |
+ | |
+ +---------|-------------------------------------------------|---------+
+ | +------v------+ +------v------+ |
+ | | | | | |
+ | | EP | | EP | |
+ | | CONTROLLER1 | | CONTROLLER2 | |
+ | | <-----------------------------------> | |
+ | | | | | |
+ | | | | | |
+ | | | SoC With Multiple EP Instances | | |
+ | | | (Configured using NTB Function) | | |
+ | +-------------+ +-------------+ |
+ +---------------------------------------------------------------------+
+
+Constructs used for Implementing NTB
+====================================
+
+ 1) Config Region
+ 2) Self Scratchpad Registers
+ 3) Peer Scratchpad Registers
+ 4) Doorbell (DB) Registers
+ 5) Memory Window (MW)
+
+
+Config Region:
+--------------
+
+Config Region is a construct that is specific to NTB implemented using NTB
+Endpoint Function Driver. The host and endpoint side NTB function driver will
+exchange information with each other using this region. Config Region has
+Control/Status Registers for configuring the Endpoint Controller. Host can
+write into this region for configuring the outbound Address Translation Unit
+(ATU) and to indicate the link status. Endpoint can indicate the status of
+commands issued by host in this region. Endpoint can also indicate the
+scratchpad offset and number of memory windows to the host using this region.
+
+The format of Config Region is given below. All the fields here are 32 bits.
+
+.. code-block:: text
+
+ +------------------------+
+ | COMMAND |
+ +------------------------+
+ | ARGUMENT |
+ +------------------------+
+ | STATUS |
+ +------------------------+
+ | TOPOLOGY |
+ +------------------------+
+ | ADDRESS (LOWER 32) |
+ +------------------------+
+ | ADDRESS (UPPER 32) |
+ +------------------------+
+ | SIZE |
+ +------------------------+
+ | NO OF MEMORY WINDOW |
+ +------------------------+
+ | MEMORY WINDOW1 OFFSET |
+ +------------------------+
+ | SPAD OFFSET |
+ +------------------------+
+ | SPAD COUNT |
+ +------------------------+
+ | DB ENTRY SIZE |
+ +------------------------+
+ | DB DATA |
+ +------------------------+
+ | : |
+ +------------------------+
+ | : |
+ +------------------------+
+ | DB DATA |
+ +------------------------+
+
+
+ COMMAND:
+
+ NTB function supports three commands:
+
+ CMD_CONFIGURE_DOORBELL (0x1): Command to configure doorbell. Before
+ invoking this command, the host should allocate and initialize
+ MSI/MSI-X vectors (i.e., initialize the MSI/MSI-X Capability in the
+ Endpoint). The endpoint on receiving this command will configure
+ the outbound ATU such that transactions to Doorbell BAR will be routed
+ to the MSI/MSI-X address programmed by the host. The ARGUMENT
+ register should be populated with number of DBs to configure (in the
+ lower 16 bits) and if MSI or MSI-X should be configured (BIT 16).
+
+ CMD_CONFIGURE_MW (0x2): Command to configure memory window (MW). The
+ host invokes this command after allocating a buffer that can be
+ accessed by remote host. The allocated address should be programmed
+ in the ADDRESS register (64 bit), the size should be programmed in
+ the SIZE register and the memory window index should be programmed
+ in the ARGUMENT register. The endpoint on receiving this command
+ will configure the outbound ATU such that transactions to MW BAR
+ are routed to the address provided by the host.
+
+ CMD_LINK_UP (0x3): Command to indicate an NTB application is
+ bound to the EP device on the host side. Once the endpoint
+ receives this command from both the hosts, the endpoint will
+ raise a LINK_UP event to both the hosts to indicate the host
+ NTB applications can start communicating with each other.
+
+ ARGUMENT:
+
+ The value of this register is based on the commands issued in
+ command register. See COMMAND section for more information.
+
+ TOPOLOGY:
+
+ Set to NTB_TOPO_B2B_USD for Primary interface
+ Set to NTB_TOPO_B2B_DSD for Secondary interface
+
+ ADDRESS/SIZE:
+
+ Address and Size to be used while configuring the memory window.
+ See "CMD_CONFIGURE_MW" for more info.
+
+ MEMORY WINDOW1 OFFSET:
+
+ Memory Window 1 and Doorbell registers are packed together in the
+ same BAR. The initial portion of the region will have doorbell
+ registers and the latter portion of the region is for memory window 1.
+ This register will specify the offset of the memory window 1.
+
+ NO OF MEMORY WINDOW:
+
+ Specifies the number of memory windows supported by the NTB device.
+
+ SPAD OFFSET:
+
+ Self scratchpad region and config region are packed together in the
+ same BAR. The initial portion of the region will have config region
+ and the latter portion of the region is for self scratchpad. This
+ register will specify the offset of the self scratchpad registers.
+
+ SPAD COUNT:
+
+ Specifies the number of scratchpad registers supported by the NTB
+ device.
+
+ DB ENTRY SIZE:
+
+ Used to determine the offset within the DB BAR that should be written
+ in order to raise doorbell. EPF NTB can use either MSI or MSI-X to
+ ring doorbell (MSI-X support will be added later). MSI uses same
+ address for all the interrupts and MSI-X can provide different
+ addresses for different interrupts. The MSI/MSI-X address is provided
+ by the host and the address it gives is based on the MSI/MSI-X
+ implementation supported by the host. For instance, ARM platform
+ using GIC ITS will have the same MSI-X address for all the interrupts.
+ In order to support all the combinations and use the same mechanism
+ for both MSI and MSI-X, EPF NTB allocates a separate region in the
+ Outbound Address Space for each of the interrupts. This region will
+ be mapped to the MSI/MSI-X address provided by the host. If a host
+ provides the same address for all the interrupts, all the regions
+ will be translated to the same address. If a host provides different
+ addresses, the regions will be translated to different addresses. This
+ will ensure there is no difference while raising the doorbell.
+
+ DB DATA:
+
+ EPF NTB supports 32 interrupts, so there are 32 DB DATA registers.
+ This holds the MSI/MSI-X data that has to be written to MSI address
+ for raising doorbell interrupt. This will be populated by EPF NTB
+ while invoking CMD_CONFIGURE_DOORBELL.
+
+Scratchpad Registers:
+---------------------
+
+ Each host has its own register space allocated in the memory of NTB endpoint
+ controller. They are both readable and writable from both sides of the bridge.
+ They are used by applications built over NTB and can be used to pass control
+ and status information between both sides of a device.
+
+ Scratchpad registers has 2 parts
+ 1) Self Scratchpad: Host's own register space
+ 2) Peer Scratchpad: Remote host's register space.
+
+Doorbell Registers:
+-------------------
+
+ Doorbell Registers are used by the hosts to interrupt each other.
+
+Memory Window:
+--------------
+
+ Actual transfer of data between the two hosts will happen using the
+ memory window.
+
+Modeling Constructs:
+====================
+
+There are 5 or more distinct regions (config, self scratchpad, peer
+scratchpad, doorbell, one or more memory windows) to be modeled to achieve
+NTB functionality. At least one memory window is required while more than
+one is permitted. All these regions should be mapped to BARs for hosts to
+access these regions.
+
+If one 32-bit BAR is allocated for each of these regions, the scheme would
+look like this:
+
+====== ===============
+BAR NO CONSTRUCTS USED
+====== ===============
+BAR0 Config Region
+BAR1 Self Scratchpad
+BAR2 Peer Scratchpad
+BAR3 Doorbell
+BAR4 Memory Window 1
+BAR5 Memory Window 2
+====== ===============
+
+However if we allocate a separate BAR for each of the regions, there would not
+be enough BARs for all the regions in a platform that supports only 64-bit
+BARs.
+
+In order to be supported by most of the platforms, the regions should be
+packed and mapped to BARs in a way that provides NTB functionality and
+also makes sure the host doesn't access any region that it is not supposed
+to.
+
+The following scheme is used in EPF NTB Function:
+
+====== ===============================
+BAR NO CONSTRUCTS USED
+====== ===============================
+BAR0 Config Region + Self Scratchpad
+BAR1 Peer Scratchpad
+BAR2 Doorbell + Memory Window 1
+BAR3 Memory Window 2
+BAR4 Memory Window 3
+BAR5 Memory Window 4
+====== ===============================
+
+With this scheme, for the basic NTB functionality 3 BARs should be sufficient.
+
+Modeling Config/Scratchpad Region:
+----------------------------------
+
+.. code-block:: text
+
+ +-----------------+------->+------------------+ +-----------------+
+ | BAR0 | | CONFIG REGION | | BAR0 |
+ +-----------------+----+ +------------------+<-------+-----------------+
+ | BAR1 | | |SCRATCHPAD REGION | | BAR1 |
+ +-----------------+ +-->+------------------+<-------+-----------------+
+ | BAR2 | Local Memory | BAR2 |
+ +-----------------+ +-----------------+
+ | BAR3 | | BAR3 |
+ +-----------------+ +-----------------+
+ | BAR4 | | BAR4 |
+ +-----------------+ +-----------------+
+ | BAR5 | | BAR5 |
+ +-----------------+ +-----------------+
+ EP CONTROLLER 1 EP CONTROLLER 2
+
+Above diagram shows Config region + Scratchpad region for HOST1 (connected to
+EP controller 1) allocated in local memory. The HOST1 can access the config
+region and scratchpad region (self scratchpad) using BAR0 of EP controller 1.
+The peer host (HOST2 connected to EP controller 2) can also access this
+scratchpad region (peer scratchpad) using BAR1 of EP controller 2. This
+diagram shows the case where Config region and Scratchpad regions are allocated
+for HOST1, however the same is applicable for HOST2.
+
+Modeling Doorbell/Memory Window 1:
+----------------------------------
+
+.. code-block:: text
+
+ +-----------------+ +----->+----------------+-----------+-----------------+
+ | BAR0 | | | Doorbell 1 +-----------> MSI-X ADDRESS 1 |
+ +-----------------+ | +----------------+ +-----------------+
+ | BAR1 | | | Doorbell 2 +---------+ | |
+ +-----------------+----+ +----------------+ | | |
+ | BAR2 | | Doorbell 3 +-------+ | +-----------------+
+ +-----------------+----+ +----------------+ | +-> MSI-X ADDRESS 2 |
+ | BAR3 | | | Doorbell 4 +-----+ | +-----------------+
+ +-----------------+ | |----------------+ | | | |
+ | BAR4 | | | | | | +-----------------+
+ +-----------------+ | | MW1 +---+ | +-->+ MSI-X ADDRESS 3||
+ | BAR5 | | | | | | +-----------------+
+ +-----------------+ +----->-----------------+ | | | |
+ EP CONTROLLER 1 | | | | +-----------------+
+ | | | +---->+ MSI-X ADDRESS 4 |
+ +----------------+ | +-----------------+
+ EP CONTROLLER 2 | | |
+ (OB SPACE) | | |
+ +-------> MW1 |
+ | |
+ | |
+ +-----------------+
+ | |
+ | |
+ | |
+ | |
+ | |
+ +-----------------+
+ PCI Address Space
+ (Managed by HOST2)
+
+Above diagram shows how the doorbell and memory window 1 is mapped so that
+HOST1 can raise doorbell interrupt on HOST2 and also how HOST1 can access
+buffers exposed by HOST2 using memory window1 (MW1). Here doorbell and
+memory window 1 regions are allocated in EP controller 2 outbound (OB) address
+space. Allocating and configuring BARs for doorbell and memory window1
+is done during the initialization phase of NTB endpoint function driver.
+Mapping from EP controller 2 OB space to PCI address space is done when HOST2
+sends CMD_CONFIGURE_MW/CMD_CONFIGURE_DOORBELL.
+
+Modeling Optional Memory Windows:
+---------------------------------
+
+This is modeled the same was as MW1 but each of the additional memory windows
+is mapped to separate BARs.
projects / platform / kernel / linux-rpi.git / commitdiff