[PATCH 7/7] scsi: mpt3sas: Introduce sas_ncq_prio_supported sysfs sttribute

[Damien Le Moal <damien.lemoal@wdc.com>]

Similarly to AHCI, introduce the device sysfs attribute
sas_ncq_prio_supported to advertize 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 priroity commands.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
---
 drivers/scsi/mpt3sas/mpt3sas_ctl.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/scsi/mpt3sas/mpt3sas_ctl.c b/drivers/scsi/mpt3sas/mpt3sas_ctl.c
index b66140e4c370..7bce8288fb4f 100644
--- a/drivers/scsi/mpt3sas/mpt3sas_ctl.c
+++ b/drivers/scsi/mpt3sas/mpt3sas_ctl.c
@@ -3918,6 +3918,25 @@ 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 desciptor
+ * @buf: the buffer returned
+ *
+ * A sysfs 'read/write' 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 snprintf(buf, PAGE_SIZE, "%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
@@ -3960,6 +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,
 };
-- 
2.31.1