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libata: use PIO for non-16 byte aligned ATAPI commands 

The IDE driver used DMA for ATAPI commands if READ/WRITE command is
multiple of sector size or sg command is multiple of 16 bytes.  For
libata, READ/WRITE sector alignment is guaranteed by the high level
driver (sr), so we only have to worry about the 16 byte alignment.

This patch makes ata_check_atapi_dma() always request PIO for all data
transfer commands which are not multiple of 16 bytes.

The following reports are related to this problem.

http://bugzilla.kernel.org/show_bug.cgi?id=8605		(confirmed)
http://thread.gmane.org/gmane.linux.kernel/476620	(confirmed)
https://bugzilla.novell.com/show_bug.cgi?id=229260	(probably)

Albert first pointed out the difference between IDE and libata.  Kudos
to him.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Albert Lee <albertcc@tw.ibm.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
This commit is contained in:
Tejun Heo 2007-06-27 02:48:43 +09:00 committed by Jeff Garzik
parent e00f1ff3c8
commit b9a4197e26
1 changed files with 9 additions and 22 deletions
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31
drivers/ata/libata-core.c
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@ -4109,6 +4109,7 @@ static void ata_fill_sg(struct ata_queued_cmd *qc)
if (idx)
ap->prd[idx - 1].flags_len |= cpu_to_le32(ATA_PRD_EOT);
}
/**
* ata_check_atapi_dma - Check whether ATAPI DMA can be supported
* @qc: Metadata associated with taskfile to check
@ -4126,33 +4127,19 @@ static void ata_fill_sg(struct ata_queued_cmd *qc)
int ata_check_atapi_dma(struct ata_queued_cmd *qc)
{
struct ata_port *ap = qc->ap;
int rc = 0; /* Assume ATAPI DMA is OK by default */
/* some drives can only do ATAPI DMA on read/write */
if (unlikely(qc->dev->horkage & ATA_HORKAGE_DMA_RW_ONLY)) {
struct scsi_cmnd *cmd = qc->scsicmd;
u8 *scsicmd = cmd->cmnd;
switch (scsicmd[0]) {
case READ_10:
case WRITE_10:
case READ_12:
case WRITE_12:
case READ_6:
case WRITE_6:
/* atapi dma maybe ok */
break;
default:
/* turn off atapi dma */
return 1;
}
}
/* Don't allow DMA if it isn't multiple of 16 bytes. Quite a
* few ATAPI devices choke on such DMA requests.
*/
if (unlikely(qc->nbytes & 15))
return 1;
if (ap->ops->check_atapi_dma)
rc = ap->ops->check_atapi_dma(qc);
return ap->ops->check_atapi_dma(qc);
return rc;
return 0;
}
/**
* ata_qc_prep - Prepare taskfile for submission
* @qc: Metadata associated with taskfile to be prepared