diff options
| -rw-r--r-- | drivers/usb/storage/uas.c | 18 |
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; } |
