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uas: Make sure sg elements are properly aligned

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Copy the sg alignment trick from the usb-storage driver, without this I'm
seeing intermittent errors when using uas devices with an ehci controller.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
This commit is contained in:
Hans de Goede 2013-11-15 10:04:31 +01:00 committed by Sarah Sharp
parent 8e453155d7
commit 37599f9603
1 changed files with 18 additions and 0 deletions
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18
drivers/usb/storage/uas.c
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@ -925,6 +925,24 @@ static int uas_eh_bus_reset_handler(struct scsi_cmnd *cmnd)
static int uas_slave_alloc(struct scsi_device *sdev)
{
sdev->hostdata = (void *)sdev->host->hostdata;
/* USB has unusual DMA-alignment requirements: Although the
* starting address of each scatter-gather element doesn't matter,
* the length of each element except the last must be divisible
* by the Bulk maxpacket value. There's currently no way to
* express this by block-layer constraints, so we'll cop out
* and simply require addresses to be aligned at 512-byte
* boundaries. This is okay since most block I/O involves
* hardware sectors that are multiples of 512 bytes in length,
* and since host controllers up through USB 2.0 have maxpacket
* values no larger than 512.
*
* But it doesn't suffice for Wireless USB, where Bulk maxpacket
* values can be as large as 2048. To make that work properly
* will require changes to the block layer.
*/
blk_queue_update_dma_alignment(sdev->request_queue, (512 - 1));
return 0;
}