From: James Bottomley Date: Tue, 1 Jan 2008 16:00:10 +0000 (-0600) Subject: [SCSI] relax scsi dma alignment X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commitdiff_plain;h=465ff3185e0cb76d46137335a4d21d0d9d3ac8a2 [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 Signed-off-by: James Bottomley --- diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c index 264ae60..4bb268b 100644 --- a/drivers/ata/libata-scsi.c +++ b/drivers/ata/libata-scsi.c @@ -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; } /** diff --git a/drivers/firewire/fw-sbp2.c b/drivers/firewire/fw-sbp2.c index 624ff3e..c2169d2 100644 --- a/drivers/firewire/fw-sbp2.c +++ b/drivers/firewire/fw-sbp2.c @@ -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; diff --git a/drivers/ieee1394/sbp2.c b/drivers/ieee1394/sbp2.c index b83d254..1eda11a 100644 --- a/drivers/ieee1394/sbp2.c +++ b/drivers/ieee1394/sbp2.c @@ -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; diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index db52222..de60137 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -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); 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 @@ 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).