Re: [PATCH v2] thermal_hwmon: Fix the 'No sensors found' error after replacing the parameter NULL by the actual device

[Cao Van Dong <cv-dong@jinso.co.jp>]

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Dear Marc-san,

Thanks for your comment!

>> Formerly, when registering the hwmon device, we pass NULL as the 
>> device. It's not a problem.
>> Recently, the developer has replaced the parameter NULL as the device 
>> by the actual device.
>> This causes the "No sensors found" error. Therefore, instead of using 
>> the device we will use pass
>
> What does report this error? Is it a userspace application?

Below are the comments of Guente-san:
  " The "No sensors found" message is from the "sensors" application.
    The device type associated with the passed device is unknown to
    libsensors (it is parsed from the parent device subsystem name -
    what is that, anyway ?). This could be addressed in libsensors,
    or the thermal subsystem could attach itself to a known subsystem,
    or the thermal subsystem must pass a pointer the parent device. "

I think the problem is the thermal subsystem must pass a pointer the 
parent device.

>> the parent of that device as parameter. This will sync with the 
>> processor on the hwmon core.
>> This patch is to fix this error.
>>
>> This patch is based on the v4.19-rc3 tag.
>>
>> ---
>
> This patch has no SoB.

I will add SoB later.

>>   drivers/thermal/thermal_hwmon.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/thermal/thermal_hwmon.c 
>> b/drivers/thermal/thermal_hwmon.c
>> index 40c69a5..a918ba9 100644
>> --- a/drivers/thermal/thermal_hwmon.c
>> +++ b/drivers/thermal/thermal_hwmon.c
>> @@ -143,7 +143,7 @@ int thermal_add_hwmon_sysfs(struct 
>> thermal_zone_device *tz)
>>       INIT_LIST_HEAD(&hwmon->tz_list);
>>       strlcpy(hwmon->type, tz->type, THERMAL_NAME_LENGTH);
>>       strreplace(hwmon->type, '-', '_');
>> -    hwmon->device = hwmon_device_register_with_info(&tz->device, 
>> hwmon->type,
>> +    hwmon->device = 
>> hwmon_device_register_with_info(tz->device.parent, hwmon->type,
>>                               hwmon, NULL, NULL);
>>       if (IS_ERR(hwmon->device)) {
>>           result = PTR_ERR(hwmon->device);
>>
>
> It is not clear to me that this is any better. What is the parent 
> device in this case? Can you give an example of what breaks in the 
> hierarchy?
>
> Given how close we are to to 4.19, I'd rather we revert 
> f6b6b52ef7a54160 if there are userspace visible regressions.
>

Initially, I considered your patch to be correct and went to look at the 
processor in the hwmon core. Then I created the v1 patch.
After patch v1, I noticed that it is necessary to check for cases where 
the device has parent and if there is no parent.
However, when looking at function hwmon_device_register_with_info() and 
its header, I see that the device parameter passed in
must be the parent device ("* @dev: the parent device"). Therefore, I 
think it's best to pass a parent device parameter to this function.
So, I decided to create this v2 patch.


Regards,
Dong/Jinso



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