[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 7c9593b..dd8b13e 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).