linux-kernel - [PATCH] hwmon: (pmbus) Clear pmbus fault/warning bits before read

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Date:   Thu, 10 Feb 2022 12:41:54 +0000
From:   Vikash Chandola <vikash.chandola@...ux.intel.com>
To:     iwona.winiarska@...el.com, linux@...ck-us.net, jdelvare@...e.com,
        linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Vikash Chandola <vikash.chandola@...ux.intel.com>
Subject: [PATCH] hwmon: (pmbus) Clear pmbus fault/warning bits before read

pmbus fault and warning bits are not cleared by itself once fault/warning
condition is not valid anymore. As per pmbus datasheet faults must be
cleared by user.
Modify hwmon behavior to clear latched status bytes if any bit in status
register is high prior to returning fresh data to userspace. If
fault/warning conditions are still applicable fault/warning bits will be
set and we will get updated data in second read.

Hwmon behavior is changed here. Now sysfs reads will reflect latest
values from pmbus slave, not latched values.
In case a transient warning/fault has happened in the past, it will no
longer be reported to userspace.

Signed-off-by: Vikash Chandola <vikash.chandola@...ux.intel.com>
---
 drivers/hwmon/pmbus/pmbus_core.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
index 776ee2237be2..1cc82d644079 100644
--- a/drivers/hwmon/pmbus/pmbus_core.c
+++ b/drivers/hwmon/pmbus/pmbus_core.c
@@ -577,6 +577,15 @@ static int pmbus_get_status(struct i2c_client *client, int page, int reg)
 		break;
 	default:
 		status = _pmbus_read_byte_data(client, page, reg);
+		if (status > 0) {
+			/*
+			 * Status greater than 0 could mean that there was a fault/warning.
+			 * Clear faults and do a second read to make sure we are not getting
+			 * stale values.
+			 */
+			pmbus_clear_fault_page(client, page);
+			status = _pmbus_read_byte_data(client, page, reg);
+		}
 		break;
 	}
 	if (status < 0)
-- 
2.25.1