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 <[EMAIL PROTECTED]> Cc: Albert Lee <[EMAIL PROTECTED]> --- drivers/ata/libata-core.c | 31 +++++++++---------------------- 1 file changed, 9 insertions(+), 22 deletions(-) Index: work/drivers/ata/libata-core.c =================================================================== --- work.orig/drivers/ata/libata-core.c +++ work/drivers/ata/libata-core.c @@ -4109,6 +4109,7 @@ static void ata_fill_sg(struct ata_queue 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_queue 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 - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
