linux-kernel - Re: [PATCH] arm64: dts: juno: align thermal zone names with bindings

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Message-ID: <cbe43d1e-8de8-4f05-887c-a34b45ee327f@linaro.org>
Date: Wed, 3 Jan 2024 14:39:06 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Rob Herring <robh+dt@...nel.org>
Cc: Liviu Dudau <liviu.dudau@....com>, Sudeep Holla <sudeep.holla@....com>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, linux-arm-kernel@...ts.infradead.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: juno: align thermal zone names with bindings

On 03/01/2024 11:13, Krzysztof Kozlowski wrote:
> 
>> 'pinctrl-[0-9]+'
>>       4  thermal-zones: gpu1-thermal: 'trips' is a required property
>>       4  thermal-zones: gpu0-thermal: 'trips' is a required property
>>       4  thermal-zones: big-cluster-thermal: 'trips' is a required property
>>
>> Last I checked this, it looked like the length of the child names was
>> limited because the thermal subsys uses the node names for its naming
>> which is limited to 20 chars (with null). Though the regex here allows
>> for 21 chars without nul. Looks like a double off by one error.
> 
> Yes, that's another issue.
> 
>>
>> The thought I had at the time was to make the kernel drop '-thermal'
>> from its names. Might be an (Linux) ABI issue if userspace cares (I
>> think it shouldn't). Also, I'm not sure how the kernel handles the
>> names overflowing. Maybe it is fine and we can just extend the length
>> in the schema from 12 to 18 (plus the 1 starting char).
> 
> The name is used in the "/sys/class/thermal/thermal_zone0/type" file, so
> actually some userspace could depend on it, but it would be affected
> anyway by my renaming of nodes.

Stripping "-thermal" prefix is a bit bigger task, because it is later
used to find the actual nodes. The thermal framework does not store
device_node pointer, but looks up by the name.

There is on-going work around this:
https://lore.kernel.org/all/20231012175836.3408077-2-thierry.reding@gmail.com/

https://lore.kernel.org/all/20231221124825.149141-27-angelogioacchino.delregno@collabora.com/

so I will just fix the DTS (shorten the name) and fix bindings for 11
characters.

Best regards,
Krzysztof