linux-kernel - Re: [PATCH 7/8] hwmon: (scmi) Register explicitly with Thermal Framework

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Message-ID: <7acc7a49-debb-abdb-f01c-f8adef4c1f0e@roeck-us.net>
Date:   Fri, 28 Oct 2022 09:34:05 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Cristian Marussi <cristian.marussi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        sudeep.holla@....com, Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-hwmon@...r.kernel.org
Subject: Re: [PATCH 7/8] hwmon: (scmi) Register explicitly with Thermal
 Framework

On 10/28/22 09:15, Cristian Marussi wrote:
> On Fri, Oct 28, 2022 at 08:58:58AM -0700, Guenter Roeck wrote:
>> On 10/28/22 08:35, Cristian Marussi wrote:
>> [ ... ]
>>>>> +	/*
>>>>> +	 * Try to register a temperature sensor with the Thermal Framework:
>>>>> +	 * skip sensors not defined as part of any thermal zone (-ENODEV) but
>>>>> +	 * report any other errors related to misconfigured zones/sensors.
>>>>> +	 */
>>>>> +	tzd = devm_thermal_of_zone_register(dev, th_sensor->info->id, th_sensor,
>>>>> +					    &scmi_hwmon_thermal_ops);
>>>>> +	if (IS_ERR(tzd)) {
>>>>> +		devm_kfree(dev, th_sensor);
>>>>> +
>>>>> +		if (PTR_ERR(tzd) != -ENODEV)
>>>>> +			return PTR_ERR(tzd);
>>>>> +
>>>>> +		dev_info(dev, "Sensor '%s' not attached to any thermal zone.\n",
>>>>> +			 sensor->name);
>>>>
>>>> There were complaints about this message as it is noisy. If you send
>>>> another version, please drop it unless attaching each sensor to a thermal
>>>> zone is strongly expected. If you don't send another version, I'll drop it
>>>> while applying.
>>>>
>>>
>>> Ok fine for me. I am waiting to have some feedback from Sudeep too, but
>>> I do not have plan for another version as of now.
>>>
>>> As a side note, though, I understand the 'noisiness' argument, but,
>>> sincerely this same message in the original HWMON code was the only
>>> reason why I spotted that something was wrong with the SCMI/HWMON
>>> interactions and discovered the indexes/ids mismatch...if not for
>>> that it would have gone un-noticed that a perfectly configured
>>> ThermalZone/Sensor was not working properly...
>>> (un-noticed at least until something would have been burnt to fire
>>>    in my house .. joking :P)
>>>
>>
>> Good point.
>>
>> Did you ever check the returned error code ? Maybe we could use it to
>> distinguish "it is not attached to a thermal zone because it is not
>> associated with one" from "attaching to a thermal zone failed because
>> its configuration is bad/incomplete".
>>
> 
> Yes, it is what I do already indeed, in this regards I mimicked what
> the hwmon-thermal bridge was doing.
> 
> In scmi_thermal_sensor_register() this message is printed out only
> if Thermal registration returned -ENODEV and no err is reported
> (which means teh specified sensor was not found attached to any TZ),
> while in the caller of scmi_thermal_sensor_register() for any error
> returned but -ENOMEM I print:
> 
> 	"Thermal zone misconfigured for %s. err=%d\n",
> 
> since any error reported by Thermal other than ENODEV and ENOMEM
> means the DT parsing unveiled some configuration anomaly.
> 

Ok, then let's hope that this finds misconfigurations and drop the
info message.

I just noticed another problem in your code:

+		if (ret == -ENOMEM)
+			return ret;
+		else if (ret)
+			dev_warn(dev,
+				 "Thermal zone misconfigured for %s. err=%d\n",
+				 sensor->name, ret);

Static analyzers will rightfully notice that else after return is unnecessary.
Please rewrite and drop the else. I think something like

		if (ret) {
			if (ret == -ENOMEM)
				return ret;
			dev_warn(dev,
				 "Thermal zone misconfigured for %s. err=%d\n",
				 sensor->name, ret);
		}

would be better since ret would only be evaluated once in the no-error case.

Thanks,
Guenter