linux-kernel - Re: [PATCH v2] hwmon: (pmbus/ibm-cffps) Add clear

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Date:   Wed, 16 Mar 2022 13:11:59 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Brandon Wyman <bjwyman@...il.com>
Cc:     Joel Stanley <joel@....id.au>,
        OpenBMC Maillist <openbmc@...ts.ozlabs.org>,
        Eddie James <eajames@...ux.ibm.com>,
        Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] hwmon: (pmbus/ibm-cffps) Add clear_faults debugfs
 entry

On 3/16/22 13:03, Brandon Wyman wrote:
> On Sun, Mar 13, 2022 at 11:36 PM Guenter Roeck <linux@...ck-us.net> wrote:
>>
>> On 3/11/22 10:10, Brandon Wyman wrote:
>>> Add a clear_faults write-only debugfs entry for the ibm-cffps device
>>> driver.
>>>
>>> Certain IBM power supplies require clearing some latched faults in order
>>> to indicate that the fault has indeed been observed/noticed.
>>>
>>
>> That is insufficient, sorry. Please provide the affected power supplies as
>> well as the affected faults, and confirm that the problem still exists
>> in v5.17-rc6 or later kernels - or, more specifically, in any kernel which
>> includes commit 35f165f08950 ("hwmon: (pmbus) Clear pmbus fault/warning
>> bits after read").
>>
>> Thanks,
>> Guenter
> 
> Sorry for the delay in responding. I did some testing with commit
> 35f165f08950. I could not get that code to send the CLEAR_FAULTS
> command to the power supplies.
> 
> I can update the commit message to be more specific about which power
> supplies need this CLEAR_FAULTS sent, and which faults. It is observed
> with the 1600W power supplies (2B1E model). The faults that latch are
> the VIN_UV and INPUT faults in the STATUS_WORD. The corresponding
> STATUS_INPUT fault bits are VIN_UV_FAULT and Unit is Off.
> 

The point is that the respective fault bits should be reset when the
corresponding alarm attributes are read. This isn't about executing
a CLEAR_FAULTS command, but about selectively resetting fault bits
while ensuring that faults are reported at least once. Executing
CLEAR_FAULTS is a big hammer.

With the patch I pointed to in place, input (and other) faults should
be reset after the corresponding alarm attributes are read, assuming
that the condition no longer exists. If that does not happen, we should
fix the problem instead of deploying the big hammer.

Thanks,
Guenter

>>
>>> Signed-off-by: Brandon Wyman <bjwyman@...il.com>
>>> ---
>>> V1 -> V2: Explain why this change is needed
>>>
>>>    drivers/hwmon/pmbus/ibm-cffps.c | 11 +++++++++++
>>>    1 file changed, 11 insertions(+)
>>>
>>> diff --git a/drivers/hwmon/pmbus/ibm-cffps.c b/drivers/hwmon/pmbus/ibm-cffps.c
>>> index e3294a1a54bb..3f02dde02a4b 100644
>>> --- a/drivers/hwmon/pmbus/ibm-cffps.c
>>> +++ b/drivers/hwmon/pmbus/ibm-cffps.c
>>> @@ -67,6 +67,7 @@ enum {
>>>        CFFPS_DEBUGFS_CCIN,
>>>        CFFPS_DEBUGFS_FW,
>>>        CFFPS_DEBUGFS_ON_OFF_CONFIG,
>>> +     CFFPS_DEBUGFS_CLEAR_FAULTS,
>>>        CFFPS_DEBUGFS_NUM_ENTRIES
>>>    };
>>>
>>> @@ -274,6 +275,13 @@ static ssize_t ibm_cffps_debugfs_write(struct file *file,
>>>                if (rc)
>>>                        return rc;
>>>
>>> +             rc = 1;
>>> +             break;
>>> +     case CFFPS_DEBUGFS_CLEAR_FAULTS:
>>> +             rc = i2c_smbus_write_byte(psu->client, PMBUS_CLEAR_FAULTS);
>>> +             if (rc < 0)
>>> +                     return rc;
>>> +
>>>                rc = 1;
>>>                break;
>>>        default:
>>> @@ -607,6 +615,9 @@ static int ibm_cffps_probe(struct i2c_client *client)
>>>        debugfs_create_file("on_off_config", 0644, ibm_cffps_dir,
>>>                            &psu->debugfs_entries[CFFPS_DEBUGFS_ON_OFF_CONFIG],
>>>                            &ibm_cffps_fops);
>>> +     debugfs_create_file("clear_faults", 0200, ibm_cffps_dir,
>>> +                         &psu->debugfs_entries[CFFPS_DEBUGFS_CLEAR_FAULTS],
>>> +                         &ibm_cffps_fops);
>>>
>>>        return 0;
>>>    }
>>