hwmon: (occ) Add temp sensor value check

The occ driver supports two formats for the temp sensor value.

The OCC firmware for P8 supports only the first format, for which
no range checking or error processing is performed in the driver.
Inspecting the OCC sources for P8 reveals that OCC may send
a special value 0xFFFF to indicate that a sensor read timeout
has occurred, see

https://github.com/open-power/occ/blob/master_p8/src/occ/cmdh/cmdh_fsp_cmds.c#L395

That situation wasn't handled in the driver. This patch adds invalid
temp value check for the sensor data format 1 and handles it the same
way as it is done for the format 2, where EREMOTEIO is reported for
this case.

Signed-off-by: Alexander Soldatov <a.soldatov@yadro.com>
Signed-off-by: Alexander Amelkin <a.amelkin@yadro.com>
Reviewed-by: Alexander Amelkin <a.amelkin@yadro.com>
Cc: Edward A. James <eajames@us.ibm.com>
Cc: Joel Stanley <joel@jms.id.au>
Reviewed-by: Eddie James <eajames@linux.ibm.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/occ/common.c

@@ -241,6 +241,12 @@ static ssize_t occ_show_temp_1(struct device *dev,
 		val = get_unaligned_be16(&temp->sensor_id);
 		break;
 	case 1:
+		/*
+		 * If a sensor reading has expired and couldn't be refreshed,
+		 * OCC returns 0xFFFF for that sensor.
+		 */
+		if (temp->value == 0xFFFF)
+			return -EREMOTEIO;
 		val = get_unaligned_be16(&temp->value) * 1000;
 		break;
 	default: