[PATCH] libata-eh-fw: use special reserved tag and qc for internal commands

New EH may issue internal commands to recover from error while failed
qc's are still hanging around.  To allow such usage, reserve tag
ATA_MAX_QUEUE-1 for internal command.  This also makes it easy to tell
whether a qc is for internal command or not.  ata_tag_internal() test
implements this test.

To avoid breaking existing drivers, ata_exec_internal() uses
ATA_TAG_INTERNAL only for drivers which implement ->error_handler.
For drivers using old EH, tag 0 is used.  Note that this makes
ata_tag_internal() test valid only when ->error_handler is
implemented.  This is okay as drivers on old EH should not and does
not have any reason to use ata_tag_internal().

Signed-off-by: Tejun Heo <htejun@gmail.com>

drivers/scsi/libata-core.c

diff --git a/drivers/scsi/libata-core.c b/drivers/scsi/libata-core.c
index de2cd61..966abb5 100644
--- a/drivers/scsi/libata-core.c
+++ b/drivers/scsi/libata-core.c
@@ -980,15 +980,39 @@
 	struct ata_port *ap = dev->ap;
 	u8 command = tf->command;
 	struct ata_queued_cmd *qc;
+	unsigned int tag, preempted_tag;
 	DECLARE_COMPLETION(wait);
 	unsigned long flags;
 	unsigned int err_mask;
 
 	spin_lock_irqsave(&ap->host_set->lock, flags);
 
-	qc = ata_qc_new_init(dev);
-	BUG_ON(qc == NULL);
+	/* initialize internal qc */
 
+	/* XXX: Tag 0 is used for drivers with legacy EH as some
+	 * drivers choke if any other tag is given.  This breaks
+	 * ata_tag_internal() test for those drivers.  Don't use new
+	 * EH stuff without converting to it.
+	 */
+	if (ap->ops->error_handler)
+		tag = ATA_TAG_INTERNAL;
+	else
+		tag = 0;
+
+	if (test_and_set_bit(tag, &ap->qactive))
+		BUG();
+	qc = ata_qc_from_tag(ap, tag);
+
+	qc->tag = tag;
+	qc->scsicmd = NULL;
+	qc->ap = ap;
+	qc->dev = dev;
+	ata_qc_reinit(qc);
+
+	preempted_tag = ap->active_tag;
+	ap->active_tag = ATA_TAG_POISON;
+
+	/* prepare & issue qc */
 	qc->tf = *tf;
 	if (cdb)
 		memcpy(qc->cdb, cdb, ATAPI_CDB_LEN);
@@ -1035,6 +1059,7 @@
 	err_mask = qc->err_mask;
 
 	ata_qc_free(qc);
+	ap->active_tag = preempted_tag;
 
 	/* XXX - Some LLDDs (sata_mv) disable port on command failure.
 	 * Until those drivers are fixed, we detect the condition
@@ -4014,7 +4039,8 @@
 	struct ata_queued_cmd *qc = NULL;
 	unsigned int i;
 
-	for (i = 0; i < ATA_MAX_QUEUE; i++)
+	/* the last tag is reserved for internal command. */
+	for (i = 0; i < ATA_MAX_QUEUE - 1; i++)
 		if (!test_and_set_bit(i, &ap->qactive)) {
 			qc = ata_qc_from_tag(ap, i);
 			break;

include/linux/libata.h

diff --git a/include/linux/libata.h b/include/linux/libata.h
index e5d6d7f..5a403e4 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -108,7 +108,9 @@
 	LIBATA_MAX_PRD		= ATA_MAX_PRD / 2,
 	ATA_MAX_PORTS		= 8,
 	ATA_DEF_QUEUE		= 1,
-	ATA_MAX_QUEUE		= 1,
+	/* tag ATA_MAX_QUEUE - 1 is reserved for internal commands */
+	ATA_MAX_QUEUE		= 2,
+	ATA_TAG_INTERNAL	= ATA_MAX_QUEUE - 1,
 	ATA_MAX_SECTORS		= 200,	/* FIXME */
 	ATA_MAX_BUS		= 2,
 	ATA_DEF_BUSY_WAIT	= 10000,
@@ -717,6 +719,11 @@
 	return (tag < ATA_MAX_QUEUE) ? 1 : 0;
 }
 
+static inline unsigned int ata_tag_internal(unsigned int tag)
+{
+	return tag == ATA_MAX_QUEUE - 1;
+}
+
 static inline unsigned int ata_class_enabled(unsigned int class)
 {
 	return class == ATA_DEV_ATA || class == ATA_DEV_ATAPI;