[libata] comments and constants

* note a nasty problem with shared interrupts that must be fixed
  before we turn on certain code paths.
* add a few comments to the READ CAPACITY scsi simulator
* remove a FIXME comment from the TEST UNIT READY scsi simulator
* add constant for ATA command CHECK POWER MODE, and associated
  "mandatory" power management feature set bit.

drivers/scsi/libata-core.c

@@ -2634,6 +2634,8 @@ inline unsigned int ata_host_intr (struct ata_port *ap,
 	unsigned int handled = 0;
 
 	switch (qc->tf.protocol) {
+
+	/* BMDMA completion */
 	case ATA_PROT_DMA:
 	case ATA_PROT_ATAPI_DMA:
 		if (ap->flags & ATA_FLAG_MMIO) {
@@ -2652,8 +2654,16 @@ inline unsigned int ata_host_intr (struct ata_port *ap,
 		handled = 1;
 		break;
 
+	/* command completion, but no data xfer */
+	/* FIXME: a shared interrupt _will_ cause a non-data command
+	 * to be completed prematurely, with an error.
+	 *
+	 * This doesn't matter right now, since we aren't sending
+	 * non-data commands down this pipe except in development
+	 * situations.
+	 */
 	case ATA_PROT_ATAPI:
-	case ATA_PROT_NODATA:	/* command completion, but no data xfer */
+	case ATA_PROT_NODATA:
 		status = ata_busy_wait(ap, ATA_BUSY | ATA_DRQ, 1000);
 		DPRINTK("BUS_NODATA (drv_stat 0x%X)\n", status);
 		ata_qc_complete(qc, status);

drivers/scsi/libata-scsi.c

@@ -812,20 +812,23 @@ unsigned int ata_scsiop_read_cap(struct ata_scsi_args *args, u8 *rbuf,
 
 	VPRINTK("ENTER\n");
 
-	n_sectors--;		/* one off */
+	n_sectors--;		/* ATA TotalUserSectors - 1 */
 
 	tmp = n_sectors;	/* note: truncates, if lba48 */
 	if (args->cmd->cmnd[0] == READ_CAPACITY) {
+		/* sector count, 32-bit */
 		rbuf[0] = tmp >> (8 * 3);
 		rbuf[1] = tmp >> (8 * 2);
 		rbuf[2] = tmp >> (8 * 1);
 		rbuf[3] = tmp;
 
+		/* sector size */
 		tmp = ATA_SECT_SIZE;
 		rbuf[6] = tmp >> 8;
 		rbuf[7] = tmp;
 
 	} else {
+		/* sector count, 64-bit */
 		rbuf[2] = n_sectors >> (8 * 7);
 		rbuf[3] = n_sectors >> (8 * 6);
 		rbuf[4] = n_sectors >> (8 * 5);
@@ -835,6 +838,7 @@ unsigned int ata_scsiop_read_cap(struct ata_scsi_args *args, u8 *rbuf,
 		rbuf[8] = tmp >> (8 * 1);
 		rbuf[9] = tmp;
 
+		/* sector size */
 		tmp = ATA_SECT_SIZE;
 		rbuf[12] = tmp >> 8;
 		rbuf[13] = tmp;
@@ -1114,7 +1118,7 @@ static void ata_scsi_simulate(struct ata_port *ap, struct ata_device *dev,
 	args.done = done;
 
 	switch(scsicmd[0]) {
-		case TEST_UNIT_READY:		/* FIXME: correct? */
+		case TEST_UNIT_READY:
 		case FORMAT_UNIT:		/* FIXME: correct? */
 		case SEND_DIAGNOSTIC:		/* FIXME: correct? */
 			ata_scsi_rbuf_fill(&args, ata_scsiop_noop);

include/linux/ata.h

@@ -104,6 +104,7 @@ enum {
 	ATA_REG_IRQ		= ATA_REG_NSECT,
 
 	/* ATA device commands */
+	ATA_CMD_CHK_POWER	= 0xE5, /* check power mode */
 	ATA_CMD_EDD		= 0x90,	/* execute device diagnostic */
 	ATA_CMD_FLUSH		= 0xE7,
 	ATA_CMD_FLUSH_EXT	= 0xEA,
@@ -204,6 +205,7 @@ struct ata_taskfile {
 #define ata_id_wcache_enabled(dev) ((dev)->id[85] & (1 << 5))
 #define ata_id_has_lba48(dev)	((dev)->id[83] & (1 << 10))
 #define ata_id_has_wcache(dev)	((dev)->id[82] & (1 << 5))
+#define ata_id_has_pm(dev)	((dev)->id[82] & (1 << 3))
 #define ata_id_has_lba(dev)	((dev)->id[49] & (1 << 8))
 #define ata_id_has_dma(dev)	((dev)->id[49] & (1 << 9))
 #define ata_id_removeable(dev)	((dev)->id[0] & (1 << 7))