libata: Improve ATA queued command allocation

Improve ATA queued command allocation as follows:

- For attaining a qc tag for a SAS host we need to allocate a bit in
  ata_port.sas_tag_allocated bitmap.

  However we already have a unique tag per device in range
  [0, ATA_MAX_QUEUE -1] in the scsi cmnd budget token, so just use that
  instead.

- It is a bit pointless to have ata_qc_new_init() in libata-core.c since it
  pokes scsi internals, so inline it in ata_scsi_qc_new() (in
  libata-scsi.c). Also update Doc accordingly.

- Use standard SCSI helpers set_host_byte() and set_status_byte() in
  ata_scsi_qc_new().

Christoph Hellwig originally contributed the change to inline
ata_qc_new_init().

Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>

1 files changed, 35 insertions, 11 deletions

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 06c9d90238d9..42cecf95a4e5 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -638,24 +638,48 @@ EXPORT_SYMBOL_GPL(ata_scsi_ioctl);
 static struct ata_queued_cmd *ata_scsi_qc_new(struct ata_device *dev,
 					      struct scsi_cmnd *cmd)
 {
+	struct ata_port *ap = dev->link->ap;
 	struct ata_queued_cmd *qc;
+	int tag;
 
-	qc = ata_qc_new_init(dev, scsi_cmd_to_rq(cmd)->tag);
-	if (qc) {
-		qc->scsicmd = cmd;
-		qc->scsidone = scsi_done;
-
-		qc->sg = scsi_sglist(cmd);
-		qc->n_elem = scsi_sg_count(cmd);
+	if (unlikely(ap->pflags & ATA_PFLAG_FROZEN))
+		goto fail;
 
-		if (scsi_cmd_to_rq(cmd)->rq_flags & RQF_QUIET)
-			qc->flags |= ATA_QCFLAG_QUIET;
+	if (ap->flags & ATA_FLAG_SAS_HOST) {
+		/*
+		 * SAS hosts may queue > ATA_MAX_QUEUE commands so use
+		 * unique per-device budget token as a tag.
+		 */
+		if (WARN_ON_ONCE(cmd->budget_token >= ATA_MAX_QUEUE))
+			goto fail;
+		tag = cmd->budget_token;
 	} else {
-		cmd->result = (DID_OK << 16) | SAM_STAT_TASK_SET_FULL;
-		scsi_done(cmd);
+		tag = scsi_cmd_to_rq(cmd)->tag;
 	}
 
+	qc = __ata_qc_from_tag(ap, tag);
+	qc->tag = qc->hw_tag = tag;
+	qc->ap = ap;
+	qc->dev = dev;
+
+	ata_qc_reinit(qc);
+
+	qc->scsicmd = cmd;
+	qc->scsidone = scsi_done;
+
+	qc->sg = scsi_sglist(cmd);
+	qc->n_elem = scsi_sg_count(cmd);
+
+	if (scsi_cmd_to_rq(cmd)->rq_flags & RQF_QUIET)
+		qc->flags |= ATA_QCFLAG_QUIET;
+
 	return qc;
+
+fail:
+	set_host_byte(cmd, DID_OK);
+	set_status_byte(cmd, SAM_STAT_TASK_SET_FULL);
+	scsi_done(cmd);
+	return NULL;
 }
 
 static void ata_qc_set_pc_nbytes(struct ata_queued_cmd *qc)