[SCSI] relax scsi dma alignment

This patch relaxes the default SCSI DMA alignment from 512 bytes to 4
bytes.  I remember from previous discussions that usb and firewire have
sector size alignment requirements, so I upped their alignments in the
respective slave allocs.

The reason for doing this is so that we don't get such a huge amount of
copy overhead in bio_copy_user() for udev.  (basically all inquiries it
issues can now be directly mapped).

Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/firewire/fw-sbp2.c b/drivers/firewire/fw-sbp2.c
index 624ff3e082f6..c2169d215bf7 100644
--- a/drivers/firewire/fw-sbp2.c
+++ b/drivers/firewire/fw-sbp2.c
@@ -1238,6 +1238,12 @@ static int sbp2_scsi_slave_alloc(struct scsi_device *sdev)
 
         sdev->allow_restart = 1;
 
+        /*
+         * Update the dma alignment (minimum alignment requirements for
+         * start and end of DMA transfers) to be a sector
+         */
+        blk_queue_update_dma_alignment(sdev->request_queue, 511);
+
         if (lu->tgt->workarounds & SBP2_WORKAROUND_INQUIRY_36)
                 sdev->inquiry_len = 36;