libata: introduce notion of separate hardware tags

Rigth now these are the same, but drivers should be using ->hw_tag
for their command setup and issue.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Tejun Heo <tj@kernel.org>

drivers/ata/libata-core.c

@@ -1600,7 +1600,7 @@ unsigned ata_exec_internal_sg(struct ata_device *dev,
 
 	qc = __ata_qc_from_tag(ap, tag);
 
-	qc->tag = tag;
+	qc->tag = qc->hw_tag = tag;
 	qc->scsicmd = NULL;
 	qc->ap = ap;
 	qc->dev = dev;
@@ -5125,7 +5125,7 @@ struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev, int tag)
 	}
 
 	qc = __ata_qc_from_tag(ap, tag);
-	qc->tag = tag;
+	qc->tag = qc->hw_tag = tag;
 	qc->scsicmd = NULL;
 	qc->ap = ap;
 	qc->dev = dev;

include/linux/libata.h

@@ -637,7 +637,8 @@ struct ata_queued_cmd {
 	u8			cdb[ATAPI_CDB_LEN];
 
 	unsigned long		flags;		/* ATA_QCFLAG_xxx */
-	unsigned int		tag;
+	unsigned int		tag;		/* libata core tag */
+	unsigned int		hw_tag;		/* driver tag */
 	unsigned int		n_elem;
 	unsigned int		orig_n_elem;