[PATCH] hwmon: Conditionally clear individual status bits for pmbus rev >= 1.2

[Patryk Biel]

This change adds fetching PMBus revision and using it to conditionally
clear individual status bits while calling pmbus_show_boolean, only if
the device is compliant with PMBus specs >= 1.2.

Signed-off-by: Patryk Biel <pbiel7@xxxxxxxxx>
---
Current implementation of pmbus_show_boolean assumes that all devices
support write-back operation of status register so as to clear pending
warning or faults. Since clearing individual bits in the status registers
was introduced in PMBus specification 1.2, this operation may not be 
supported by some older devices, thus resulting in error while reading 
boolean attributes like e.g. temp1_max_alarm. 

This change adds fetching PMBus revision supported by device and
modifies pmbus_show_boolean so that it only tries to clear individual
status bits if the device is compilant with PMBus specs >= 1.2.

Tested on: LTC2971, LTC2971-1, LTC2974, LTC2977.
---
 drivers/hwmon/pmbus/pmbus.h      |  6 ++++++
 drivers/hwmon/pmbus/pmbus_core.c | 12 +++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/hwmon/pmbus/pmbus.h b/drivers/hwmon/pmbus/pmbus.h
index fb442fae7b3e..0bea603994e7 100644
--- a/drivers/hwmon/pmbus/pmbus.h
+++ b/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 */
diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
index cb4c65a7f288..50ba093a38e8 100644
--- a/drivers/hwmon/pmbus/pmbus_core.c
+++ b/drivers/hwmon/pmbus/pmbus_core.c
@@ -108,6 +108,8 @@ struct pmbus_data {
 
 	int vout_low[PMBUS_PAGES];	/* voltage low margin */
 	int vout_high[PMBUS_PAGES];	/* voltage high margin */
+
+	u8 revision;	/* The PMBus revision the device is compliant with */
 };
 
 struct pmbus_debugfs_entry {
@@ -1095,7 +1097,11 @@ 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 (data->revision >= PMBUS_REV_12)
+			ret = _pmbus_write_byte_data(client, page, reg, regval);
+		else
+			pmbus_clear_fault_page(client, page);
+
 		if (ret)
 			goto unlock;
 	}
@@ -2653,6 +2659,10 @@ static int pmbus_init_common(struct i2c_client *client, struct pmbus_data *data,
 		}
 	}
 
+	ret = i2c_smbus_read_byte_data(client, PMBUS_REVISION);
+	if (ret > 0)
+		data->revision = ret;
+
 	if (info->pages <= 0 || info->pages > PMBUS_PAGES) {
 		dev_err(dev, "Bad number of PMBus pages: %d\n", info->pages);
 		return -ENODEV;

---
base-commit: c763c43396883456ef57e5e78b64d3c259c4babc
change-id: 20240905-pmbus-status-reg-clearing-abc9c0184c3b

Best regards,
-- 
Patryk Biel <pbiel7@xxxxxxxxx>