scsi: pm80xx: Add sysfs attribute to track iop0 count

A new sysfs variable 'ctl_iop0_count' is being introduced that tells if
the controller is alive by indicating controller ticks. If on subsequent
run we see the ticks changing that indicates that controller is not
dead.

Using the 'ctl_iop0_count' sysfs variable we can see ticks incrementing:

    linux-9saw:~# cat /sys/class/scsi_host/host*/ctl_iop0_count
    0x000000a3
    0x000001db
    0x000001e4
    0x000001e7

Link: https://lore.kernel.org/r/20210415103352.3580-5-Viswas.G@microchip.comAcked-by: Jack Wang <jinpu.wang@ionos.com>
Signed-off-by: Vishakha Channapattan <vishakhavc@google.com>
Signed-off-by: Viswas G <Viswas.G@microchip.com>
Signed-off-by: Ruksar Devadi <Ruksar.devadi@microchip.com>
Signed-off-by: Ashokkumar N <Ashokkumar.N@microchip.com>
Signed-off-by: Radha Ramachandran <radha@google.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/pm8001/pm8001_ctl.c

@@ -953,6 +953,27 @@ static ssize_t ctl_raae_count_show(struct device *cdev,
 }
 static DEVICE_ATTR_RO(ctl_raae_count);
 
+/**
+ * ctl_iop0_count_show - controller iop0 count check
+ * @cdev: pointer to embedded class device
+ * @buf: the buffer returned
+ *
+ * A sysfs 'read-only' shost attribute.
+ */
+
+static ssize_t ctl_iop0_count_show(struct device *cdev,
+		struct device_attribute *attr, char *buf)
+{
+	struct Scsi_Host *shost = class_to_shost(cdev);
+	struct sas_ha_struct *sha = SHOST_TO_SAS_HA(shost);
+	struct pm8001_hba_info *pm8001_ha = sha->lldd_ha;
+	unsigned int iop0cnt;
+
+	iop0cnt = pm8001_mr32(pm8001_ha->general_stat_tbl_addr, 16);
+	return sysfs_emit(buf, "0x%08x\n", iop0cnt);
+}
+static DEVICE_ATTR_RO(ctl_iop0_count);
+
 struct device_attribute *pm8001_host_attrs[] = {
 	&dev_attr_interface_rev,
 	&dev_attr_controller_fatal_error,
@@ -979,6 +1000,7 @@ struct device_attribute *pm8001_host_attrs[] = {
 	&dev_attr_ctl_mpi_state,
 	&dev_attr_ctl_hmi_error,
 	&dev_attr_ctl_raae_count,
+	&dev_attr_ctl_iop0_count,
 	NULL,
 };