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>

1 files changed, 10 insertions, 23 deletions

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 642097a7d60d..094b51891dbf 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -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