summaryrefslogtreecommitdiff
path: root/drivers/usb/storage
diff options
context:
space:
mode:
authorHans de Goede <hdegoede@redhat.com>2013-11-15 10:04:31 +0100
committerSarah Sharp <sarah.a.sharp@linux.intel.com>2014-03-04 15:38:26 -0800
commit37599f9603bed3d72becdc1a59c164576df9fbfc (patch)
treeebb571b8a52b0c708d889609a50e09b4897f204c /drivers/usb/storage
parent8e453155d7f8dfa53863ba6f8da6c68f7c17ece4 (diff)
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>
Diffstat (limited to 'drivers/usb/storage')
-rw-r--r--drivers/usb/storage/uas.c18
1 files changed, 18 insertions, 0 deletions
diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c
index 62086829af14..ad97615b75b1 100644
--- 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;
}