[libata] handle non-data ATAPI commands via interrupt

It's easier to do it this way, than polling, at the moment.

Also, fix a test in ata_scsi_translate that was incorrectly
erroring-out non-data commands.

drivers/scsi/libata-core.c

@@ -2677,6 +2677,7 @@ inline unsigned int ata_host_intr (struct ata_port *ap,
 		handled = 1;
 		break;
 
+	case ATA_PROT_ATAPI:
 	case ATA_PROT_NODATA:	/* command completion, but no data xfer */
 		status = ata_busy_wait(ap, ATA_BUSY | ATA_DRQ, 1000);
 		DPRINTK("BUS_NODATA (drv_stat 0x%X)\n", status);
@@ -2837,9 +2838,16 @@ static void atapi_packet_task(void *_data)
 	      qc->scsicmd->cmnd, ap->host->max_cmd_len / 4);
 
 	/* if we are DMA'ing, irq handler takes over from here */
-	if (qc->tf.protocol == ATA_PROT_ATAPI_DMA) {
+	if (qc->tf.protocol == ATA_PROT_ATAPI_DMA)
 		ap->ops->bmdma_start(qc);	    /* initiate bmdma */
-	} else {
+
+	/* non-data commands are also handled via irq */
+	else if (qc->scsicmd->sc_data_direction == SCSI_DATA_NONE) {
+		/* do nothing */
+	}
+
+	/* PIO commands are handled by polling */
+	else {
 		ap->pio_task_state = PIO_ST;
 		queue_work(ata_wq, &ap->pio_task);
 	}

drivers/scsi/libata-scsi.c

@@ -362,19 +362,20 @@ static void ata_scsi_translate(struct ata_port *ap, struct ata_device *dev,
 
 	VPRINTK("ENTER\n");
 
-	if (unlikely(cmd->request_bufflen < 1)) {
-		printk(KERN_WARNING "ata%u(%u): empty request buffer\n",
-		       ap->id, dev->devno);
-		goto err_out;
-	}
-
 	qc = ata_scsi_qc_new(ap, dev, cmd, done);
 	if (!qc)
 		return;
 
 	if (cmd->sc_data_direction == SCSI_DATA_READ ||
-	    cmd->sc_data_direction == SCSI_DATA_WRITE)
+	    cmd->sc_data_direction == SCSI_DATA_WRITE) {
+		if (unlikely(cmd->request_bufflen < 1)) {
+			printk(KERN_WARNING "ata%u(%u): WARNING: zero len r/w req\n",
+			       ap->id, dev->devno);
+			goto err_out;
+		}
+
 		qc->flags |= ATA_QCFLAG_SG; /* data is present; dma-map it */
+	}
 
 	if (xlat_func(qc, scsicmd))
 		goto err_out;
@@ -910,12 +911,18 @@ static unsigned int atapi_xlat(struct ata_queued_cmd *qc, u8 *scsicmd)
 
 	qc->tf.command = ATA_CMD_PACKET;
 
-	if ((cmd->sc_data_direction == SCSI_DATA_NONE) ||
-	    ((qc->flags & ATA_QCFLAG_DMA) == 0)) {
+	/* no data - interrupt-driven */
+	if (cmd->sc_data_direction == SCSI_DATA_NONE)
+		qc->tf.protocol = ATA_PROT_ATAPI;
+
+	/* PIO data xfer - polling */
+	else if ((qc->flags & ATA_QCFLAG_DMA) == 0) {
 		ata_qc_set_polling(qc);
 		qc->tf.protocol = ATA_PROT_ATAPI;
 		qc->tf.lbam = (8 * 1024) & 0xff;
 		qc->tf.lbah = (8 * 1024) >> 8;
+
+	/* DMA data xfer - interrupt-driven */
 	} else {
 		qc->flags |= ATA_QCFLAG_SG; /* data is present; dma-map it */
 		qc->tf.protocol = ATA_PROT_ATAPI_DMA;