diff options
| author | James Bottomley <James.Bottomley@HansenPartnership.com> | 2008-01-01 10:00:10 -0600 |
|---|---|---|
| committer | James Bottomley <James.Bottomley@HansenPartnership.com> | 2008-01-11 18:29:22 -0600 |
| commit | 465ff3185e0cb76d46137335a4d21d0d9d3ac8a2 (patch) | |
| tree | 171068cd7d99600cd094c2eb72bac712649fd9eb /drivers/usb | |
| parent | 11c3e689f1c3a73e3af7b0ea767b1b0626da8033 (diff) | |
| download | linux-465ff3185e0cb76d46137335a4d21d0d9d3ac8a2.tar.bz2 | |
[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>
Diffstat (limited to 'drivers/usb')
| -rw-r--r-- | drivers/usb/storage/scsiglue.c | 20 |
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). |