Commit 465ff318 authored by James Bottomley's avatar James Bottomley
Browse files

[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: default avatarAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: default avatarJames Bottomley <James.Bottomley@HansenPartnership.com>
parent 11c3e689
......@@ -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;
}
/**
......
......@@ -1238,6 +1238,12 @@ static int sbp2_scsi_slave_alloc(struct scsi_device *sdev)
sdev->allow_restart = 1;
/*
* Update the dma alignment (minimum alignment requirements for
* start and end of DMA transfers) to be a sector
*/
blk_queue_update_dma_alignment(sdev->request_queue, 511);
if (lu->tgt->workarounds & SBP2_WORKAROUND_INQUIRY_36)
sdev->inquiry_len = 36;
......
......@@ -1963,6 +1963,12 @@ static int sbp2scsi_slave_alloc(struct scsi_device *sdev)
lu->sdev = sdev;
sdev->allow_restart = 1;
/*
* Update the dma alignment (minimum alignment requirements for
* start and end of DMA transfers) to be a sector
*/
blk_queue_update_dma_alignment(sdev->request_queue, 511);
if (lu->workarounds & SBP2_WORKAROUND_INQUIRY_36)
sdev->inquiry_len = 36;
return 0;
......
......@@ -1668,6 +1668,14 @@ struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
if (!shost->use_clustering)
clear_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
/*
* set a reasonable default alignment on word boundaries: the
* host and device may alter it using
* blk_queue_update_dma_alignment() later.
*/
blk_queue_dma_alignment(q, 0x03);
return q;
}
EXPORT_SYMBOL(__scsi_alloc_queue);
......
......@@ -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).
......
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