[libata] random minor bug fixes

* Only call ata_sg_setup{_one} if ATA_QCFLAG_SG is set.  Preparation
  for future use, as currently ATA_QCFLAG_SG is always set when
  ata_qc_issue is called.

  This change in theory is incorrect for Promise TX/SX4 drivers,
  since those drivers set up the Promise-specific packet in their
  ->fill_sg hook, which is now called conditionally.

  A FIXME that doesn't affect anything, for now.

* ATA_PROT_ATAPI and ATA_PROT_ATAPI_DMA command issue need to be
  differentiated.

* Create and use ata_qc_set_polling() to consistently set/clear the
  flags associated with using polling instead of interrupts.

drivers/scsi/libata-core.c

@@ -2396,16 +2396,18 @@ int ata_qc_issue(struct ata_queued_cmd *qc)
 	struct ata_port *ap = qc->ap;
 	struct scsi_cmnd *cmd = qc->scsicmd;
 
-	/* set up SG table */
-	if (cmd->use_sg) {
-		if (ata_sg_setup(qc))
-			goto err_out;
-	} else {
-		if (ata_sg_setup_one(qc))
-			goto err_out;
-	}
+	if (qc->flags & ATA_QCFLAG_SG) {
+		/* set up SG table */
+		if (cmd->use_sg) {
+			if (ata_sg_setup(qc))
+				goto err_out;
+		} else {
+			if (ata_sg_setup_one(qc))
+				goto err_out;
+		}
 
-	ap->ops->fill_sg(qc);
+		ap->ops->fill_sg(qc);
+	}
 
 	qc->ap->active_tag = qc->tag;
 	qc->flags |= ATA_QCFLAG_ACTIVE;
@@ -2450,14 +2452,17 @@ static int ata_qc_issue_prot(struct ata_queued_cmd *qc)
 		break;
 
 	case ATA_PROT_PIO: /* load tf registers, initiate polling pio */
-		qc->flags |= ATA_QCFLAG_POLL;
-		qc->tf.ctl |= ATA_NIEN;	/* disable interrupts */
+		ata_qc_set_polling(qc);
 		ata_tf_to_host_nolock(ap, &qc->tf);
 		ap->pio_task_state = PIO_ST;
 		queue_work(ata_wq, &ap->pio_task);
 		break;
 
 	case ATA_PROT_ATAPI:
+		ata_tf_to_host_nolock(ap, &qc->tf);
+		queue_work(ata_wq, &ap->packet_task);
+		break;
+
 	case ATA_PROT_ATAPI_DMA:
 		ap->ops->tf_load(ap, &qc->tf);	 /* load tf registers */
 		ap->ops->bmdma_setup(qc);	    /* set up bmdma */

drivers/scsi/libata-scsi.c

@@ -912,9 +912,8 @@ static unsigned int atapi_xlat(struct ata_queued_cmd *qc, u8 *scsicmd)
 
 	if ((cmd->sc_data_direction == SCSI_DATA_NONE) ||
 	    ((qc->flags & ATA_QCFLAG_DMA) == 0)) {
-		qc->flags |= ATA_QCFLAG_POLL;
+		ata_qc_set_polling(qc);
 		qc->tf.protocol = ATA_PROT_ATAPI;
-		qc->tf.ctl |= ATA_NIEN;	/* disable interrupts */
 		qc->tf.lbam = (8 * 1024) & 0xff;
 		qc->tf.lbah = (8 * 1024) >> 8;
 	} else {

include/linux/libata.h

@@ -481,6 +481,13 @@ static inline u8 ata_wait_idle(struct ata_port *ap)
 	return status;
 }
 
+static inline void ata_qc_set_polling(struct ata_queued_cmd *qc)
+{
+	qc->flags |= ATA_QCFLAG_POLL;
+	qc->flags &= ~ATA_QCFLAG_DMA;
+	qc->tf.ctl |= ATA_NIEN;
+}
+
 static inline struct ata_queued_cmd *ata_qc_from_tag (struct ata_port *ap,
 						      unsigned int tag)
 {