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path: root/drivers/usb/storage/scsiglue.c
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Diffstat (limited to 'drivers/usb/storage/scsiglue.c')
-rw-r--r--drivers/usb/storage/scsiglue.c26
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));