[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, 4 insertions, 1 deletions

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 264ae60e3fd8..4bb268b9aaeb 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -824,6 +824,9 @@ static void ata_scsi_sdev_config(struct scsi_device *sdev)
          * requests.
          */
         sdev->max_device_blocked = 1;
+
+        /* set the min alignment */
+        blk_queue_update_dma_alignment(sdev->request_queue, ATA_DMA_PAD_SZ - 1);
 }
 
 static void ata_scsi_dev_config(struct scsi_device *sdev,
@@ -878,7 +881,7 @@ int ata_scsi_slave_config(struct scsi_device *sdev)
         if (dev)
                 ata_scsi_dev_config(sdev, dev);
 
-        return 0;       /* scsi layer doesn't check return value, sigh */
+        return 0;
 }
 
 /**