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 6208682..ad97615 100644
--- a/drivers/usb/storage/uas.c
+++ b/drivers/usb/storage/uas.c
@@ -925,6 +925,24 @@
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;
}