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Subject: Re: [PATCH v4 04/11] thermal: Store device mode in struct
 thermal_zone_device
To:     Andrzej Pietrasiewicz <andrzej.p@collabora.com>
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From:   Guenter Roeck <linux@roeck-us.net>
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Message-ID: <3776b295-eb43-ce3c-0d9a-c923a3bd5ffd@roeck-us.net>
Date:   Fri, 29 May 2020 12:08:46 -0700
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On 5/29/20 10:21 AM, Andrzej Pietrasiewicz wrote:
> Hi again,
> 
> W dniu 29.05.2020 o 18:08, Andrzej Pietrasiewicz pisze:
>> Hi Guenter,
>>
>> W dniu 29.05.2020 o 17:42, Guenter Roeck pisze:
>>> On Thu, May 28, 2020 at 09:20:44PM +0200, Andrzej Pietrasiewicz wrote:
>>>> Prepare for eliminating get_mode().
>>>>
>>> Might be worthwhile to explain (not only in the subject) what you are
>>> doing here.
>>>
>>>> Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
>>>> ---
>>>>   drivers/acpi/thermal.c                        | 18 ++++++----------
>>>>   .../ethernet/mellanox/mlxsw/core_thermal.c    | 21 +++++++------------
>>>>   drivers/platform/x86/acerhdf.c                | 15 ++++++-------
>>>>   drivers/thermal/da9062-thermal.c              |  6 ++----
>>>>   drivers/thermal/imx_thermal.c                 | 17 +++++++--------
>>>>   .../intel/int340x_thermal/int3400_thermal.c   | 12 +++--------
>>>>   .../thermal/intel/intel_quark_dts_thermal.c   | 16 +++++++-------
>>>>   drivers/thermal/thermal_of.c                  | 10 +++------
>>>
>>> After this patch is applied on top of the thermal 'testing' branch,
>>> there are still local instances of thermal_device_mode in
>>>     drivers/thermal/st/stm_thermal.c
>>>     drivers/thermal/ti-soc-thermal/ti-thermal-common.c
>>>
>>> If there is a reason not to replace those, it might make sense to explain
>>> it here.
>>>
>>
>> My understanding is that these two are sensor devices which are "plugged"
>> into their "parent" thermal zone device. The latter is the "proper" tzd.
>> They both use thermal_zone_of_device_ops instead of thermal_zone_device_ops.
>> The former doesn't even have get_mode(). The thermal core, when it calls
>> get_mode(), operates on the "parent" thermal zone devices.
>>
>> Consequently, the drivers you mention use their "mode" members for
>> their private purpose, not for the purpose of storing the "parent"
>> thermal zone device mode.
>>
> 
> Let me also say it differently.
> 
> Both drivers which you mention use devm_thermal_zone_of_sensor_register().
> It calls thermal_zone_of_sensor_register(), which "will search the list of
> thermal zones described in device tree and look for the zone that refer to
> the sensor device pointed by @dev->of_node as temperature providers. For
> the zone pointing to the sensor node, the sensor will be added to the DT
> thermal zone device." When a match is found thermal_zone_of_add_sensor()
> is invoked, which (using thermal_zone_get_zone_by_name()) iterates over
> all registered thermal_zone_devices. The one eventually found will be
> returned and propagated to the original caller of
> devm_thermal_zone_of_sensor_register(). The state of this returned
> device is managed elsewhere (in that device's struct tzd). The "mode"
> member you are referring to is thus unrelated.
> 

Quite confusing, especially since the ti-soc driver doesn't seem to use
the variable at all after setting it, and the stm_thermal driver uses it
to reflect power status associated with suspend/resume. So, yes, I agree
this is fine.

Thanks,
Guenter

> Regards,
> 
> Andrzej