hwmon: (pmbus) Conditionally clear individual status bits for pmbus rev >= 1.2

The current implementation of pmbus_show_boolean assumes that all devices
support write-back operation of status register to clear pending warnings
or faults. Since clearing individual bits in the status registers was only
introduced in PMBus specification 1.2, this operation may not be supported
by some older devices. This can result in an error while reading boolean
attributes such as temp1_max_alarm.

Fetch PMBus revision supported by the device and modify pmbus_show_boolean
so that it only tries to clear individual status bits if the device is
compliant with PMBus specs >= 1.2. Otherwise clear all fault indicators
on the current page after a fault status was reported.

Fixes: 35f165f0 ("hwmon: (pmbus) Clear pmbus fault/warning bits after read")
Signed-off-by: Patryk Biel <pbiel7@gmail.com>
Message-ID: <20240909-pmbus-status-reg-clearing-v1-1-f1c0d68c6408@gmail.com>
[groeck:
 Rewrote description
 Moved revision detection code ahead of clear faults command
 Assigned revision if return value from PMBUS_REVISION command is 0
 Improved return value check from calling _pmbus_write_byte_data()]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/pmbus/pmbus.h

@@ -418,6 +418,12 @@ enum pmbus_sensor_classes {
 enum pmbus_data_format { linear = 0, ieee754, direct, vid };
 enum vrm_version { vr11 = 0, vr12, vr13, imvp9, amd625mv };
 
+/* PMBus revision identifiers */
+#define PMBUS_REV_10 0x00	/* PMBus revision 1.0 */
+#define PMBUS_REV_11 0x11	/* PMBus revision 1.1 */
+#define PMBUS_REV_12 0x22	/* PMBus revision 1.2 */
+#define PMBUS_REV_13 0x33	/* PMBus revision 1.3 */
+
 struct pmbus_driver_info {
 	int pages;		/* Total number of pages */
 	u8 phases[PMBUS_PAGES];	/* Number of phases per page */

drivers/hwmon/pmbus/pmbus_core.c

@@ -85,6 +85,8 @@ struct pmbus_data {
 
 	u32 flags;		/* from platform data */
 
+	u8 revision;	/* The PMBus revision the device is compliant with */
+
 	int exponent[PMBUS_PAGES];
 				/* linear mode: exponent for output voltages */
 
@@ -1095,9 +1097,14 @@ static int pmbus_get_boolean(struct i2c_client *client, struct pmbus_boolean *b,
 
 	regval = status & mask;
 	if (regval) {
-		ret = _pmbus_write_byte_data(client, page, reg, regval);
-		if (ret)
-			goto unlock;
+		if (data->revision >= PMBUS_REV_12) {
+			ret = _pmbus_write_byte_data(client, page, reg, regval);
+			if (ret)
+				goto unlock;
+		} else {
+			pmbus_clear_fault_page(client, page);
+		}
+
 	}
 	if (s1 && s2) {
 		s64 v1, v2;
@@ -2640,6 +2647,10 @@ static int pmbus_init_common(struct i2c_client *client, struct pmbus_data *data,
 			data->flags |= PMBUS_WRITE_PROTECTED | PMBUS_SKIP_STATUS_CHECK;
 	}
 
+	ret = i2c_smbus_read_byte_data(client, PMBUS_REVISION);
+	if (ret >= 0)
+		data->revision = ret;
+
 	if (data->info->pages)
 		pmbus_clear_faults(client);
 	else