ufs: Fix queue depth handling for best effort cases

Some UFS devices may expose bLUQueueDepth field as zero indicating
that the queue depth depends on the number of resources available
for LUN at a particular instant to handle the outstanding transfer
requests. Currently, when response for SCSI command is TASK_FULL
the LLD decrements the queue depth but fails to increment when the
resources are available. The scsi mid-layer handles the change in
queue depth heuristically and offers simple interface with
->change_queue_depth.

Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>
Signed-off-by: Dolev Raviv <draviv@codeaurora.org>
Acked-by: Santosh Y <santoshsy@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/scsi/ufs/ufshcd.c

@@ -1991,26 +1991,54 @@ static int ufshcd_slave_alloc(struct scsi_device *sdev)
 
 	/* allow SCSI layer to restart the device in case of errors */
 	sdev->allow_restart = 1;
+
 	lun_qdepth = ufshcd_read_sdev_qdepth(hba, sdev);
-	if (lun_qdepth == 0 || lun_qdepth > hba->nutrs) {
-		dev_info(hba->dev, "%s, lun %d queue depth is %d\n", __func__,
-				sdev->lun, lun_qdepth);
+	if (lun_qdepth <= 0)
+		/* eventually, we can figure out the real queue depth */
 		lun_qdepth = hba->nutrs;
-	} else if (lun_qdepth < 0) {
-		lun_qdepth = 1;
-	}
+	else
+		lun_qdepth = min_t(int, lun_qdepth, hba->nutrs);
 
-	/*
-	 * Inform SCSI Midlayer that the LUN queue depth is same as the
-	 * controller queue depth. If a LUN queue depth is less than the
-	 * controller queue depth and if the LUN reports
-	 * SAM_STAT_TASK_SET_FULL, the LUN queue depth will be adjusted
-	 * with scsi_adjust_queue_depth.
-	 */
+	dev_dbg(hba->dev, "%s: activate tcq with queue depth %d\n",
+			__func__, lun_qdepth);
 	scsi_activate_tcq(sdev, lun_qdepth);
+
 	return 0;
 }
 
+/**
+ * ufshcd_change_queue_depth - change queue depth
+ * @sdev: pointer to SCSI device
+ * @depth: required depth to set
+ * @reason: reason for changing the depth
+ *
+ * Change queue depth according to the reason and make sure
+ * the max. limits are not crossed.
+ */
+int ufshcd_change_queue_depth(struct scsi_device *sdev, int depth, int reason)
+{
+	struct ufs_hba *hba = shost_priv(sdev->host);
+
+	if (depth > hba->nutrs)
+		depth = hba->nutrs;
+
+	switch (reason) {
+	case SCSI_QDEPTH_DEFAULT:
+	case SCSI_QDEPTH_RAMP_UP:
+		if (!sdev->tagged_supported)
+			depth = 1;
+		scsi_adjust_queue_depth(sdev, scsi_get_tag_type(sdev), depth);
+		break;
+	case SCSI_QDEPTH_QFULL:
+		scsi_track_queue_full(sdev, depth);
+		break;
+	default:
+		return -EOPNOTSUPP;
+	}
+
+	return depth;
+}
+
 /**
  * ufshcd_slave_destroy - remove SCSI device configurations
  * @sdev: pointer to SCSI device
@@ -2063,42 +2091,6 @@ static int ufshcd_task_req_compl(struct ufs_hba *hba, u32 index, u8 *resp)
 	return ocs_value;
 }
 
-/**
- * ufshcd_adjust_lun_qdepth - Update LUN queue depth if device responds with
- *			      SAM_STAT_TASK_SET_FULL SCSI command status.
- * @cmd: pointer to SCSI command
- */
-static void ufshcd_adjust_lun_qdepth(struct scsi_cmnd *cmd)
-{
-	struct ufs_hba *hba;
-	int i;
-	int lun_qdepth = 0;
-
-	hba = shost_priv(cmd->device->host);
-
-	/*
-	 * LUN queue depth can be obtained by counting outstanding commands
-	 * on the LUN.
-	 */
-	for (i = 0; i < hba->nutrs; i++) {
-		if (test_bit(i, &hba->outstanding_reqs)) {
-
-			/*
-			 * Check if the outstanding command belongs
-			 * to the LUN which reported SAM_STAT_TASK_SET_FULL.
-			 */
-			if (cmd->device->lun == hba->lrb[i].lun)
-				lun_qdepth++;
-		}
-	}
-
-	/*
-	 * LUN queue depth will be total outstanding commands, except the
-	 * command for which the LUN reported SAM_STAT_TASK_SET_FULL.
-	 */
-	scsi_adjust_queue_depth(cmd->device, MSG_SIMPLE_TAG, lun_qdepth - 1);
-}
-
 /**
  * ufshcd_scsi_cmd_status - Update SCSI command result based on SCSI status
  * @lrb: pointer to local reference block of completed command
@@ -2120,12 +2112,6 @@ ufshcd_scsi_cmd_status(struct ufshcd_lrb *lrbp, int scsi_status)
 			  scsi_status;
 		break;
 	case SAM_STAT_TASK_SET_FULL:
-		/*
-		 * If a LUN reports SAM_STAT_TASK_SET_FULL, then the LUN queue
-		 * depth needs to be adjusted to the exact number of
-		 * outstanding commands the LUN can handle at any given time.
-		 */
-		ufshcd_adjust_lun_qdepth(lrbp->cmd);
 	case SAM_STAT_BUSY:
 	case SAM_STAT_TASK_ABORTED:
 		ufshcd_copy_sense_data(lrbp);
@@ -3156,6 +3142,7 @@ static struct scsi_host_template ufshcd_driver_template = {
 	.queuecommand		= ufshcd_queuecommand,
 	.slave_alloc		= ufshcd_slave_alloc,
 	.slave_destroy		= ufshcd_slave_destroy,
+	.change_queue_depth	= ufshcd_change_queue_depth,
 	.eh_abort_handler	= ufshcd_abort,
 	.eh_device_reset_handler = ufshcd_eh_device_reset_handler,
 	.eh_host_reset_handler   = ufshcd_eh_host_reset_handler,