scsi: mpt3sas: Introduce sas_ncq_prio_supported sysfs sttribute

Similarly to AHCI, introduce the device sysfs attribute
sas_ncq_prio_supported to advertise if a SATA device supports the NCQ
priority feature. Without this new attribute, the user can only discover if
a SATA device supports NCQ priority by trying to enable the feature use
with the sas_ncq_prio_enable sysfs device attribute, which fails when the
device does not support high prioity commands.

Link: https://lore.kernel.org/r/20210807041859.579409-11-damien.lemoal@wdc.comReviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/mpt3sas/mpt3sas_ctl.c

@@ -3919,6 +3919,24 @@ sas_device_handle_show(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RO(sas_device_handle);
 
+/**
+ * sas_ncq_prio_supported_show - Indicate if device supports NCQ priority
+ * @dev: pointer to embedded device
+ * @attr: sas_ncq_prio_supported attribute descriptor
+ * @buf: the buffer returned
+ *
+ * A sysfs 'read-only' sdev attribute, only works with SATA
+ */
+static ssize_t
+sas_ncq_prio_supported_show(struct device *dev,
+			    struct device_attribute *attr, char *buf)
+{
+	struct scsi_device *sdev = to_scsi_device(dev);
+
+	return sysfs_emit(buf, "%d\n", scsih_ncq_prio_supp(sdev));
+}
+static DEVICE_ATTR_RO(sas_ncq_prio_supported);
+
 /**
  * sas_ncq_prio_enable_show - send prioritized io commands to device
  * @dev: pointer to embedded device
@@ -3961,6 +3979,7 @@ static DEVICE_ATTR_RW(sas_ncq_prio_enable);
 struct device_attribute *mpt3sas_dev_attrs[] = {
 	&dev_attr_sas_address,
 	&dev_attr_sas_device_handle,
+	&dev_attr_sas_ncq_prio_supported,
 	&dev_attr_sas_ncq_prio_enable,
 	NULL,
 };