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Commit b9a4197e authored by Tejun Heo's avatar Tejun Heo Committed by Jeff Garzik
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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: default avatarTejun Heo <htejun@gmail.com>
Cc: Albert Lee <albertcc@tw.ibm.com>
Signed-off-by: default avatarJeff Garzik <jeff@garzik.org>
parent e00f1ff3

drivers/ata/libata-core.c

+10 −23
Original line number Diff line number Diff line
@@ -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 */



	/* 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