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[SCSI] relax scsi dma alignment

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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>
This commit is contained in:
James Bottomley
2008-01-01 10:00:10 -06:00
parent 11c3e689f1
commit 465ff3185e
5 changed files with 34 additions and 11 deletions
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20
drivers/usb/storage/scsiglue.c
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@@ -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).