usb: core: setup dma_pfn_offset for USB devices and, interfaces

If dma_pfn_offset is not inherited correctly from the host controller,
it might result in sub-optimal configuration as bounce
buffer limit might be set to less than optimal level.

Consider the mass storage device case.
USB storage driver creates a scsi host for the mass storage interface in
drivers/usb/storage/usb.c
The scsi host parent device is nothing but the the USB interface device.
Now, __scsi_init_queue() calls scsi_calculate_bounce_limit() to find out
and set the block layer bounce limit.
scsi_calculate_bounce_limit() uses dma_max_pfn(host_dev) to get the
bounce_limit. host_dev is nothing but the device representing the
mass storage interface.
If that device doesn't have the right dma_pfn_offset, then dma_max_pfn()
is messed up and the bounce buffer limit is wrong.

e.g. On Keystone 2 systems, dma_max_pfn() is 0x87FFFF and dma_mask_pfn
is 0xFFFFF. Consider a mass storage use case: Without this patch,
usb scsi host device (usb-storage) will get a dma_pfn_offset of 0 resulting
in a dma_max_pfn() of 0xFFFFF within the scsi layer
(scsi_calculate_bounce_limit()).
This will result in bounce buffers being unnecessarily used.

Hint: On 32-bit ARM platforms dma_max_pfn() = dma_mask_pfn + dma_pfn_offset

Signed-off-by: Roger Quadros <rogerq@ti.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
index 5ab5c1a..3a47077 100644 (file)
--- a/drivers/usb/core/message.c
+++ b/drivers/usb/core/message.c
@@ -1859,7 +1859,12 @@ free_interfaces:
                intf->dev.bus = &usb_bus_type;
                intf->dev.type = &usb_if_device_type;
                intf->dev.groups = usb_interface_groups;
+               /*
+                * Please refer to usb_alloc_dev() to see why we set
+                * dma_mask and dma_pfn_offset.
+                */
                intf->dev.dma_mask = dev->dev.dma_mask;
+               intf->dev.dma_pfn_offset = dev->dev.dma_pfn_offset;
                INIT_WORK(&intf->reset_ws, __usb_queue_reset_device);
                intf->minor = -1;
                device_initialize(&intf->dev);

diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
index 5e80697..5921514 100644 (file)
--- a/drivers/usb/core/usb.c
+++ b/drivers/usb/core/usb.c
@@ -440,7 +440,18 @@ struct usb_device *usb_alloc_dev(struct usb_device *parent,
        dev->dev.bus = &usb_bus_type;
        dev->dev.type = &usb_device_type;
        dev->dev.groups = usb_device_groups;
+       /*
+        * Fake a dma_mask/offset for the USB device:
+        * We cannot really use the dma-mapping API (dma_alloc_* and
+        * dma_map_*) for USB devices but instead need to use
+        * usb_alloc_coherent and pass data in 'urb's, but some subsystems
+        * manually look into the mask/offset pair to determine whether
+        * they need bounce buffers.
+        * Note: calling dma_set_mask() on a USB device would set the
+        * mask for the entire HCD, so don't do that.
+        */
        dev->dev.dma_mask = bus->controller->dma_mask;
+       dev->dev.dma_pfn_offset = bus->controller->dma_pfn_offset;
        set_dev_node(&dev->dev, dev_to_node(bus->controller));
        dev->state = USB_STATE_ATTACHED;
        dev->lpm_disable_count = 1;