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

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Date:   Thu, 10 Feb 2022 21:27:31 +0530
From:   Vikash Chandola <vikash.chandola@...ux.intel.com>
To:     Guenter Roeck <linux@...ck-us.net>, iwona.winiarska@...el.com,
        jdelvare@...e.com, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwmon: (pmbus) Clear pmbus fault/warning bits before read



On 2/10/2022 8:14 PM, Guenter Roeck wrote:
> On 2/10/22 04:41, Vikash Chandola wrote:
>> 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.
>>
> 
> 
> NACK.
> 
> Reporting that information is exactly the point of the current code.
> We _do_ want to report at least once that a problem occurred in the past,
> and only clear the warning flag(s) afterwards.
> 
> Guenter
> 
But as per current implementation we will continue to report fault even 
after fault condition is cleared. I could not find sysfs entry or any 
other means by which user/kernel can clear the faults/warnings after it 
is reported. Please point if I am missing anything.

>> 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)
>