libata: revert convert-to-block-tagging patches

This patch reverts the following three commits which convert libata to
use block layer tagging.

43a49cbdf31e812c0d8f553d433b09b421f5d52c
e013e13bf605b9e6b702adffbe2853cfc60e7806
2fca5ccf97d2c28bcfce44f5b07d85e74e3cd18e

Although using block layer tagging is the right direction, due to the
tight coupling among tag number, data structure allocation and
hardware command slot allocation, libata doesn't work correctly with
the current conversion.

The biggest problem is guaranteeing that tag 0 is always used for
non-NCQ commands. Due to the way blk-tag is implemented and how SCSI
starts and finishes requests, such guarantee can't be made. I'm not
sure whether this would actually break any low level driver but it
doesn't look like a good idea to break such assumption given the
frailty of ATA controllers.

So, for the time being, keep using the old dumb in-libata qc
allocation.

Signed-off-by: Tejun Heo <[e-mail]>
Cc: Jens Axobe <[e-mail]>
Cc: Jeff Garzik <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/ata/libata-core.c

···
 	else
 		tag = 0;
 
+	if (test_and_set_bit(tag, &ap->qc_allocated))
+		BUG();
 	qc = __ata_qc_from_tag(ap, tag);
 
 	qc->tag = tag;
···
 }
 
 /**
+ *	ata_qc_new - Request an available ATA command, for queueing
+ *	@ap: Port associated with device @dev
+ *	@dev: Device from whom we request an available command structure
+ *
+ *	LOCKING:
+ *	None.
+ */
+
+static struct ata_queued_cmd *ata_qc_new(struct ata_port *ap)
+{
+	struct ata_queued_cmd *qc = NULL;
+	unsigned int i;
+
+	/* no command while frozen */
+	if (unlikely(ap->pflags & ATA_PFLAG_FROZEN))
+		return NULL;
+
+	/* the last tag is reserved for internal command. */
+	for (i = 0; i < ATA_MAX_QUEUE - 1; i++)
+		if (!test_and_set_bit(i, &ap->qc_allocated)) {
+			qc = __ata_qc_from_tag(ap, i);
+			break;
+		}
+
+	if (qc)
+		qc->tag = i;
+
+	return qc;
+}
+
+/**
  *	ata_qc_new_init - Request an available ATA command, and initialize it
  *	@dev: Device from whom we request an available command structure
  *	@tag: command tag
···
  *	None.
  */
 
-struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev, int tag)
+struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev)
 {
 	struct ata_port *ap = dev->link->ap;
 	struct ata_queued_cmd *qc;
 
-	if (unlikely(ap->pflags & ATA_PFLAG_FROZEN))
-		return NULL;
-
-	qc = __ata_qc_from_tag(ap, tag);
+	qc = ata_qc_new(ap);
 	if (qc) {
 		qc->scsicmd = NULL;
 		qc->ap = ap;
 		qc->dev = dev;
-		qc->tag = tag;
 
 		ata_qc_reinit(qc);
 	}
 
 	return qc;
+}
+
+/**
+ *	ata_qc_free - free unused ata_queued_cmd
+ *	@qc: Command to complete
+ *
+ *	Designed to free unused ata_queued_cmd object
+ *	in case something prevents using it.
+ *
+ *	LOCKING:
+ *	spin_lock_irqsave(host lock)
+ */
+void ata_qc_free(struct ata_queued_cmd *qc)
+{
+	struct ata_port *ap = qc->ap;
+	unsigned int tag;
+
+	WARN_ON(qc == NULL);	/* ata_qc_from_tag _might_ return NULL */
+
+	qc->flags = 0;
+	tag = qc->tag;
+	if (likely(ata_tag_valid(tag))) {
+		qc->tag = ATA_TAG_POISON;
+		clear_bit(tag, &ap->qc_allocated);
+	}
 }
 
 void __ata_qc_complete(struct ata_queued_cmd *qc)

drivers/ata/libata-scsi.c

···
 {
 	struct ata_queued_cmd *qc;
 
-	if (cmd->request->tag != -1)
-		qc = ata_qc_new_init(dev, cmd->request->tag);
-	else
-		qc = ata_qc_new_init(dev, 0);
-
+	qc = ata_qc_new_init(dev);
 	if (qc) {
 		qc->scsicmd = cmd;
 		qc->scsidone = done;
···
 
 		depth = min(sdev->host->can_queue, ata_id_queue_depth(dev->id));
 		depth = min(ATA_MAX_QUEUE - 1, depth);
-
-		/*
-		 * If this device is behind a port multiplier, we have
-		 * to share the tag map between all devices on that PMP.
-		 * Set up the shared tag map here and we get automatic.
-		 */
-		if (dev->link->ap->pmp_link)
-			scsi_init_shared_tag_map(sdev->host, ATA_MAX_QUEUE - 1);
-
-		scsi_set_tag_type(sdev, MSG_SIMPLE_TAG);
-		scsi_activate_tcq(sdev, depth);
+		scsi_adjust_queue_depth(sdev, MSG_SIMPLE_TAG, depth);
 	}
 
 	return 0;
···
 		hdr[1] |= (1 << 7);
 
 	memcpy(rbuf, hdr, sizeof(hdr));
-
-	/* if ncq, set tags supported */
-	if (ata_id_has_ncq(args->id))
-		rbuf[7] |= (1 << 1);
-
 	memcpy(&rbuf[8], "ATA     ", 8);
 	ata_id_string(args->id, &rbuf[16], ATA_ID_PROD, 16);
 	ata_id_string(args->id, &rbuf[32], ATA_ID_FW_REV, 4);

drivers/ata/libata.h

···
 extern void ata_force_cbl(struct ata_port *ap);
 extern u64 ata_tf_to_lba(const struct ata_taskfile *tf);
 extern u64 ata_tf_to_lba48(const struct ata_taskfile *tf);
-extern struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev, int tag);
+extern struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev);
 extern int ata_build_rw_tf(struct ata_taskfile *tf, struct ata_device *dev,
 			   u64 block, u32 n_block, unsigned int tf_flags,
 			   unsigned int tag);
···
 extern int sata_down_spd_limit(struct ata_link *link);
 extern int ata_down_xfermask_limit(struct ata_device *dev, unsigned int sel);
 extern void ata_sg_clean(struct ata_queued_cmd *qc);
+extern void ata_qc_free(struct ata_queued_cmd *qc);
 extern void ata_qc_issue(struct ata_queued_cmd *qc);
 extern void __ata_qc_complete(struct ata_queued_cmd *qc);
 extern int atapi_check_dma(struct ata_queued_cmd *qc);
···
 extern struct ata_port *ata_port_alloc(struct ata_host *host);
 extern void ata_dev_enable_pm(struct ata_device *dev, enum link_pm policy);
 extern void ata_lpm_schedule(struct ata_port *ap, enum link_pm);
-
-/**
- *	ata_qc_free - free unused ata_queued_cmd
- *	@qc: Command to complete
- *
- *	Designed to free unused ata_queued_cmd object
- *	in case something prevents using it.
- *
- *	LOCKING:
- *	spin_lock_irqsave(host lock)
- */
-static inline void ata_qc_free(struct ata_queued_cmd *qc)
-{
-	qc->flags = 0;
-	qc->tag = ATA_TAG_POISON;
-}
 
 /* libata-acpi.c */
 #ifdef CONFIG_ATA_ACPI

include/linux/libata.h

···
 	unsigned int		cbl;	/* cable type; ATA_CBL_xxx */
 
 	struct ata_queued_cmd	qcmd[ATA_MAX_QUEUE];
+	unsigned long		qc_allocated;
 	unsigned int		qc_active;
 	int			nr_active_links; /* #links with active qcs */