libata_scsi: Fix ATAPI transfer lengths

Some controller variants snoop the ATAPI length value for Packet
transfers to do state machine and FIFO management. Thus we want to
set it properly, even for cases where it is otherwise meaningless.
Signed-off-by: NAlan Cox <alan@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NJeff Garzik <jeff@garzik.org>

drivers/ata/libata-scsi.c

@@ -2305,8 +2305,8 @@ static void atapi_request_sense(struct ata_queued_cmd *qc)
 		qc->tf.feature |= ATAPI_PKT_DMA;
 	} else {
 		qc->tf.protocol = ATA_PROT_ATAPI;
-		qc->tf.lbam = (8 * 1024) & 0xff;
-		qc->tf.lbah = (8 * 1024) >> 8;
+		qc->tf.lbam = SCSI_SENSE_BUFFERSIZE;
+		qc->tf.lbah = 0;
 	}
 	qc->nbytes = SCSI_SENSE_BUFFERSIZE;
 
@@ -2415,6 +2415,7 @@ static unsigned int atapi_xlat(struct ata_queued_cmd *qc)
 	struct ata_device *dev = qc->dev;
 	int using_pio = (dev->flags & ATA_DFLAG_PIO);
 	int nodata = (scmd->sc_data_direction == DMA_NONE);
+	unsigned int nbytes;
 
 	memset(qc->cdb, 0, dev->cdb_len);
 	memcpy(qc->cdb, scmd->cmnd, scmd->cmd_len);
@@ -2434,14 +2435,20 @@ static unsigned int atapi_xlat(struct ata_queued_cmd *qc)
 	if (!using_pio && ata_check_atapi_dma(qc))
 		using_pio = 1;
 
+	/* Some controller variants snoop this value for Packet transfers
+	   to do state machine and FIFO management. Thus we want to set it
+	   properly, and for DMA where it is effectively meaningless */
+	nbytes = min(qc->nbytes, (unsigned int)63 * 1024);
+
+	qc->tf.lbam = (nbytes & 0xFF);
+	qc->tf.lbah = (nbytes >> 8);
+
 	if (using_pio || nodata) {
 		/* no data, or PIO data xfer */
 		if (nodata)
 			qc->tf.protocol = ATA_PROT_ATAPI_NODATA;
 		else
 			qc->tf.protocol = ATA_PROT_ATAPI;
-		qc->tf.lbam = (8 * 1024) & 0xff;
-		qc->tf.lbah = (8 * 1024) >> 8;
 	} else {
 		/* DMA data xfer */
 		qc->tf.protocol = ATA_PROT_ATAPI_DMA;
@@ -2452,6 +2459,9 @@ static unsigned int atapi_xlat(struct ata_queued_cmd *qc)
 			qc->tf.feature |= ATAPI_DMADIR;
 	}
 
+
+	/* FIXME: We need to translate 0x05 READ_BLOCK_LIMITS to a MODE_SENSE
+	   as ATAPI tape drives don't get this right otherwise */
 	return 0;
 }