diff options
Diffstat (limited to 'drivers/usb/storage/scsiglue.c')
| -rw-r--r-- | drivers/usb/storage/scsiglue.c | 26 |
1 files changed, 12 insertions, 14 deletions
diff --git a/drivers/usb/storage/scsiglue.c b/drivers/usb/storage/scsiglue.c index a73ea495d5a7..59190d88fa9f 100644 --- a/drivers/usb/storage/scsiglue.c +++ b/drivers/usb/storage/scsiglue.c @@ -65,6 +65,7 @@ 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); + int maxp; /* * Set the INQUIRY transfer length to 36. We don't use any of @@ -74,20 +75,17 @@ static int slave_alloc (struct scsi_device *sdev) sdev->inquiry_len = 36; /* - * 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. + * USB has unusual scatter-gather requirements: the length of each + * scatterlist element except the last must be divisible by the + * Bulk maxpacket value. Fortunately this value is always a + * power of 2. Inform the block layer about this requirement. + */ + maxp = usb_maxpacket(us->pusb_dev, us->recv_bulk_pipe, 0); + blk_queue_virt_boundary(sdev->request_queue, maxp - 1); + + /* + * Some host controllers may have alignment requirements. + * We'll play it safe by requiring 512-byte alignment always. */ blk_queue_update_dma_alignment(sdev->request_queue, (512 - 1)); |