diff options
| -rw-r--r-- | drivers/usb/storage/scsiglue.c | 25 |
1 files changed, 15 insertions, 10 deletions
diff --git a/drivers/usb/storage/scsiglue.c b/drivers/usb/storage/scsiglue.c index b4c9e0f18a8..09779f6a817 100644 --- a/drivers/usb/storage/scsiglue.c +++ b/drivers/usb/storage/scsiglue.c @@ -71,7 +71,6 @@ static const char* host_info(struct Scsi_Host *host) static int slave_alloc (struct scsi_device *sdev) { struct us_data *us = host_to_us(sdev->host); - struct usb_host_endpoint *bulk_in_ep; /* * Set the INQUIRY transfer length to 36. We don't use any of @@ -80,16 +79,22 @@ static int slave_alloc (struct scsi_device *sdev) */ sdev->inquiry_len = 36; - /* Scatter-gather buffers (all but the last) must have a length - * divisible by the bulk maxpacket size. Otherwise a data packet - * would end up being short, causing a premature end to the data - * transfer. We'll use the maxpacket value of the bulk-IN pipe - * to set the SCSI device queue's DMA alignment mask. + /* 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. */ - bulk_in_ep = us->pusb_dev->ep_in[usb_pipeendpoint(us->recv_bulk_pipe)]; - blk_queue_update_dma_alignment(sdev->request_queue, - le16_to_cpu(bulk_in_ep->desc.wMaxPacketSize) - 1); - /* wMaxPacketSize must be a power of 2 */ + blk_queue_update_dma_alignment(sdev->request_queue, (512 - 1)); /* * The UFI spec treates the Peripheral Qualifier bits in an |