Commit 37599f96 authored by Hans de Goede's avatar Hans de Goede Committed by Sarah Sharp
Browse files

uas: Make sure sg elements are properly aligned 



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: default avatarHans de Goede <hdegoede@redhat.com>
Signed-off-by: default avatarSarah Sharp <sarah.a.sharp@linux.intel.com>
parent 8e453155

drivers/usb/storage/uas.c

+18 −0
Original line number Diff line number Diff line
@@ -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;

}