libata: make ata_exec_internal_sg honor DMADIR

libata honors DMADIR for regular commands, but not for internal commands
used (among other) during device initialisation.

This makes SATA-host-to-PATA-device bridges based on Silicon Image SiL3611
(such as "Abit Serillel 2") end up disabled when used with an ATAPI device
after a few tries.

Log output of the bridge being hot-plugged with an ATAPI drive:

  [ 9631.212901] ata1: exception Emask 0x10 SAct 0x0 SErr 0x40c0000 action 0xe frozen
  [ 9631.212913] ata1: irq_stat 0x00000040, connection status changed
  [ 9631.212923] ata1: SError: { CommWake 10B8B DevExch }
  [ 9631.212939] ata1: hard resetting link
  [ 9632.104962] ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
  [ 9632.106393] ata1.00: ATAPI: PIONEER DVD-RW  DVR-115, 1.06, max UDMA/33
  [ 9632.106407] ata1.00: applying bridge limits
  [ 9632.108151] ata1.00: configured for UDMA/33
  [ 9637.105303] ata1.00: qc timeout (cmd 0xa0)
  [ 9637.105324] ata1.00: failed to clear UNIT ATTENTION (err_mask=0x5)
  [ 9637.105335] ata1: hard resetting link
  [ 9638.044599] ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
  [ 9638.047878] ata1.00: configured for UDMA/33
  [ 9643.044933] ata1.00: qc timeout (cmd 0xa0)
  [ 9643.044953] ata1.00: failed to clear UNIT ATTENTION (err_mask=0x5)
  [ 9643.044963] ata1: limiting SATA link speed to 1.5 Gbps
  [ 9643.044971] ata1.00: limiting speed to UDMA/33:PIO3
  [ 9643.044979] ata1: hard resetting link
  [ 9643.984225] ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
  [ 9643.987471] ata1.00: configured for UDMA/33
  [ 9648.984591] ata1.00: qc timeout (cmd 0xa0)
  [ 9648.984612] ata1.00: failed to clear UNIT ATTENTION (err_mask=0x5)
  [ 9648.984619] ata1.00: disabled
  [ 9649.000593] ata1: hard resetting link
  [ 9649.939902] ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
  [ 9649.955864] ata1: EH complete

With this patch, the drive enumerates correctly when libata is loaded with
atapi_dmadir=1:

  [ 9891.810863] ata1: exception Emask 0x10 SAct 0x0 SErr 0x40c0000 action 0xe frozen
  [ 9891.810874] ata1: irq_stat 0x00000040, connection status changed
  [ 9891.810884] ata1: SError: { CommWake 10B8B DevExch }
  [ 9891.810900] ata1: hard resetting link
  [ 9892.762105] ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
  [ 9892.763544] ata1.00: ATAPI: PIONEER DVD-RW  DVR-115, 1.06, max UDMA/33, DMADIR
  [ 9892.763558] ata1.00: applying bridge limits
  [ 9892.765393] ata1.00: configured for UDMA/33
  [ 9892.786063] ata1: EH complete
  [ 9892.792062] scsi 0:0:0:0: CD-ROM            PIONEER  DVD-RW  DVR-115  1.06 PQ: 0 ANSI: 5
  [ 9892.798455] sr2: scsi3-mmc drive: 12x/12x writer dvd-ram cd/rw xa/form2 cdda tray
  [ 9892.798837] sr 0:0:0:0: Attached scsi CD-ROM sr2
  [ 9892.799109] sr 0:0:0:0: Attached scsi generic sg6 type 5

Based on a patch by Csaba Halász <csaba.halasz@gmail.com> on linux-ide:
http://marc.info/?l=linux-ide&m=136121147832295&w=2

tj: minor formatting changes.
Signed-off-by: Vincent Pelletier <plr.vincent@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org

drivers/ata/libata-core.c

@@ -1602,6 +1602,12 @@ unsigned ata_exec_internal_sg(struct ata_device *dev,
 	qc->tf = *tf;
 	if (cdb)
 		memcpy(qc->cdb, cdb, ATAPI_CDB_LEN);
+
+	/* some SATA bridges need us to indicate data xfer direction */
+	if (tf->protocol == ATAPI_PROT_DMA && (dev->flags & ATA_DFLAG_DMADIR) &&
+	    dma_dir == DMA_FROM_DEVICE)
+		qc->tf.feature |= ATAPI_DMADIR;
+
 	qc->flags |= ATA_QCFLAG_RESULT_TF;
 	qc->dma_dir = dma_dir;
 	if (dma_dir != DMA_NONE) {