[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>
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 @@
*/
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 @@
{
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).