[SCSI] qla4xxx: Add change_queue_depth API support

change_queue_depth will adjust device queuedepth upon receiving
"SAM_STAT_TASK_SET_FULL" scsi status from the target.
Also added ql4xqfulltracking command line param to enable or disable
queuefull tracking. One can disabling queuefull tracking to ensure
user set scsi device queuedepth is not altered.
Signed-off-by: Tej Parkash <tej.parkash@qlogic.com>
Signed-off-by: Vikas Chaudhary <vikas.chaudhary@qlogic.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/qla4xxx/ql4_os.c

@@ -68,6 +68,14 @@ MODULE_PARM_DESC(ql4xmaxqdepth,
 		 " Maximum queue depth to report for target devices.\n"
 		 "\t\t  Default: 32.");
 
+static int ql4xqfulltracking = 1;
+module_param(ql4xqfulltracking, int, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(ql4xqfulltracking,
+		 " Enable or disable dynamic tracking and adjustment of\n"
+		 "\t\t scsi device queue depth.\n"
+		 "\t\t  0 - Disable.\n"
+		 "\t\t  1 - Enable. (Default)");
+
 static int ql4xsess_recovery_tmo = QL4_SESS_RECOVERY_TMO;
 module_param(ql4xsess_recovery_tmo, int, S_IRUGO);
 MODULE_PARM_DESC(ql4xsess_recovery_tmo,
@@ -140,6 +148,8 @@ static int qla4xxx_slave_configure(struct scsi_device *device);
 static void qla4xxx_slave_destroy(struct scsi_device *sdev);
 static umode_t ql4_attr_is_visible(int param_type, int param);
 static int qla4xxx_host_reset(struct Scsi_Host *shost, int reset_type);
+static int qla4xxx_change_queue_depth(struct scsi_device *sdev, int qdepth,
+				      int reason);
 
 static struct qla4_8xxx_legacy_intr_set legacy_intr[] =
     QLA82XX_LEGACY_INTR_CONFIG;
@@ -159,6 +169,7 @@ static struct scsi_host_template qla4xxx_driver_template = {
 	.slave_configure	= qla4xxx_slave_configure,
 	.slave_alloc		= qla4xxx_slave_alloc,
 	.slave_destroy		= qla4xxx_slave_destroy,
+	.change_queue_depth	= qla4xxx_change_queue_depth,
 
 	.this_id		= -1,
 	.cmd_per_lun		= 3,
@@ -5251,6 +5262,15 @@ static void qla4xxx_slave_destroy(struct scsi_device *sdev)
 	scsi_deactivate_tcq(sdev, 1);
 }
 
+static int qla4xxx_change_queue_depth(struct scsi_device *sdev, int qdepth,
+				      int reason)
+{
+	if (!ql4xqfulltracking)
+		return -EOPNOTSUPP;
+
+	return iscsi_change_queue_depth(sdev, qdepth, reason);
+}
+
 /**
  * qla4xxx_del_from_active_array - returns an active srb
  * @ha: Pointer to host adapter structure.