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 <tj@kernel.org>
Cc: Jens Axobe <jens.axboe@oracle.com>
Cc: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 60 insertions, 6 deletions

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 622350d9b2e3..0cd3ad497136 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -1712,6 +1712,8 @@ unsigned ata_exec_internal_sg(struct ata_device *dev,
         else
                 tag = 0;
 
+        if (test_and_set_bit(tag, &ap->qc_allocated))
+                BUG();
         qc = __ata_qc_from_tag(ap, tag);
 
         qc->tag = tag;
@@ -4563,6 +4565,37 @@ void swap_buf_le16(u16 *buf, unsigned int buf_words)
 }
 
 /**
+ *      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
@@ -4571,20 +4604,16 @@ void swap_buf_le16(u16 *buf, unsigned int buf_words)
  *      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);
         }
@@ -4592,6 +4621,31 @@ struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev, int tag)
         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)
 {
         struct ata_port *ap = qc->ap;