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: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>

diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c
index 62086829af14e70d15f95edfe50d4a97c499db54..ad97615b75b1a507370008789eb865b11ea72fcb 100644 (file)
--- a/drivers/usb/storage/uas.c
+++ b/drivers/usb/storage/uas.c
@@ -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;
 }