[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, 10 insertions, 10 deletions

diff --git a/drivers/usb/storage/scsiglue.c b/drivers/usb/storage/scsiglue.c
index 7c9593b7b04e..dd8b13ef2414 100644
--- a/drivers/usb/storage/scsiglue.c
+++ b/drivers/usb/storage/scsiglue.c
@@ -81,6 +81,16 @@ 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.  Since high-speed bulk pipes have a maxpacket size
+         * of 512, we'll use that as the scsi device queue's DMA alignment
+         * mask.  Guaranteeing proper alignment of the first buffer will
+         * have the desired effect because, except at the beginning and
+         * the end, scatter-gather buffers follow page boundaries. */
+        blk_queue_update_dma_alignment(sdev->request_queue, (512 - 1));
+
         /*
          * The UFI spec treates the Peripheral Qualifier bits in an
          * INQUIRY result as reserved and requires devices to set them
@@ -100,16 +110,6 @@ static int slave_configure(struct scsi_device *sdev)
 {
         struct us_data *us = host_to_us(sdev->host);
 
-        /* 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.  Since high-speed bulk pipes have a maxpacket size
-         * of 512, we'll use that as the scsi device queue's DMA alignment
-         * mask.  Guaranteeing proper alignment of the first buffer will
-         * have the desired effect because, except at the beginning and
-         * the end, scatter-gather buffers follow page boundaries. */
-        blk_queue_dma_alignment(sdev->request_queue, (512 - 1));
-
         /* Many devices have trouble transfering more than 32KB at a time,
          * while others have trouble with more than 64K. At this time we
          * are limiting both to 32K (64 sectores).