Message-ID: <eda10481-d1f2-45c4-a5ff-0f26398fe6bf@roeck-us.net>
Date: Mon, 25 Nov 2024 08:41:28 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Krzysztof Kozlowski <krzk@...nel.org>, "Sung-Chi, Li"
 <lschyi@...omium.org>
Cc: Conor Dooley <conor.dooley@...rochip.com>, Lee Jones <lee@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Benson Leung <bleung@...omium.org>,
 Guenter Roeck <groeck@...omium.org>, Thomas Weißschuh
 <thomas@...ssschuh.net>, Jean Delvare <jdelvare@...e.com>,
 devicetree@...r.kernel.org, chrome-platform@...ts.linux.dev,
 linux-kernel@...r.kernel.org, linux-hwmon@...r.kernel.org
Subject: Re: [PATCH v3 2/2] dt-bindings: mfd: Add properties for thermal
 sensor cells

On 11/25/24 07:18, Krzysztof Kozlowski wrote:
> On 25/11/2024 16:13, Guenter Roeck wrote:
>> On 11/25/24 00:52, Krzysztof Kozlowski wrote:
>>> On 13/11/2024 04:05, Guenter Roeck wrote:
>>>> On 11/12/24 18:39, Sung-Chi, Li wrote:
>>>>> The cros_ec supports reading thermal values from thermal sensors
>>>>> connect to it. Add the property '#thermal-sensor-cells' bindings, such
>>>>> that thermal framework can recognize cros_ec as a valid thermal device.
>>>>>
>>>>> Signed-off-by: Sung-Chi, Li <lschyi@...omium.org>
>>>>> Acked-by: Conor Dooley <conor.dooley@...rochip.com>
>>>>> ---
>>>>>     Changes in v2:
>>>>>       - Add changes for DTS binding.
>>>>>     Changes in v3:
>>>>>       - Remove unneeded Change-Id tag in commit message.
>>>>> ---
>>>>
>>>> I can't apply this one (not in hwmon space), so
>>>>
>>>> Acked-by: Guenter Roeck <linux@...ck-us.net>
>>>>
>>>> with the assumption that Lee will pick it up.
>>>
>>> This was merged, while I was AFK, so the ship has sailed, but let me
>>> state here objection for any future discussions:
>>>
>>> NAK, this is not a thermal sensor. The commit msg explains what they
>>> want to achieve, but that's not a valid reason to add property from
>>> different class of devices.
>>>
>>> This is some hardware/temperature monitoring device or power supply, not
>>> part of SoC, not integrated into any SoC thermal zone. Calling it
>>
>> I am confused. We have several thermal sensors registering as thermal
>> zone, and fan controllers registering themselves as thermal cooling devices.
>>
>> Are you saying that this is all not permitted because they are not part
>> of a SoC ?
> 
> 
> These are fine, because they monitor or cool down the SoC.  Sensor can
> be under the die.  Fan for battery or for battery charger also would be
> fine, because it is a real cooling device.  It literally cools.
> 

Sorry, I don't get the distinction since you specifically refer to the SoC.
How about drive temperatures ? RAM temperatures ? Temperatures reported
by networking chips ? Power supply temperatures ? We have all those registering
thermal zones. The ASUS EC controller driver registers thermal zones
for its temperature sensors. Dell and HP drivers do the same.

> But treating battery charger as cooling device is not correct, IMHO.

Confused. The patch you object to isn't introducing a cooling device,
it is introducing #thermal-sensor-cells. The EC reports temperature
sensor results, and the driver wants to register those as thermal zones.
Yes, it may well be that one of those temperature sensors is close to
a battery charger, but I am not even sure if that is really the case.

> Battery charger does not cool anything down and already we have there
> properties for managing thermal and current aspects.
> 
Agreed, but unless I am missing something that isn't done here.

> BTW, if power supply bindings miss some thermal aspects, then let's grow
> the common binding first and agree on common aspects.
> 

I don't even know how the two patches are associated with power supplies
or battery chargers in the first place. All they try to do is to enable
adding the temperature sensor values reported by the EC in Chromebooks
to thermal zones. I don't recall any previous limitations on the ability
to register thermal sensors as thermal zone with the thermal subsystem,
and I am trying to understand what those limitations are.

So far my approach was "ok, someone wants to register a thermal sensor as
thermal zone - fine, let's do that. We have close to 50 thermal sensors on
a variety of devices - including but not limited to disk drives, memory,
Ethernet controllers, Ethernet PHYs, SFPs, RTCs, and ECs - registering
as thermal zones from hardware monitoring drivers. I don't recall anyone
ever saying "no, you can't do that".

I am trying to understand if some of those are inappropriate and, if so,
why that is the case.

Thanks,
Guenter

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