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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

drivers/ata/libata-scsi.c

+4 −1
Original line number Diff line number Diff line
@@ -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;

}



/**

drivers/firewire/fw-sbp2.c

+6 −0
Original line number Diff line number Diff line
@@ -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;

drivers/ieee1394/sbp2.c

+6 −0
Original line number Diff line number Diff line
@@ -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;

drivers/scsi/scsi_lib.c

+8 −0
Original line number Diff line number Diff line
@@ -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);

drivers/usb/storage/scsiglue.c

+10 −10
Original line number Diff line number Diff line
@@ -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).