linux-kernel - Re: [PATCH] arm64: dts: allwinner: Add GPU thermal trips to the SoC dtsi for A64

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Message-ID: <d8584ac7-5576-4f26-8bc8-1ecbb4bd4611@linaro.org>
Date: Mon, 19 Aug 2024 17:42:55 +0200
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: Dragan Simic <dsimic@...jaro.org>, Icenowy Zheng <uwu@...nowy.me>
Cc: linux-sunxi@...ts.linux.dev, wens@...e.org, jernej.skrabec@...il.com,
 samuel@...lland.org, linux-arm-kernel@...ts.infradead.org,
 devicetree@...r.kernel.org, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, linux-kernel@...r.kernel.org, wenst@...omium.org,
 broonie@...nel.org
Subject: Re: [PATCH] arm64: dts: allwinner: Add GPU thermal trips to the SoC
 dtsi for A64

On 12/08/2024 04:46, Dragan Simic wrote:
> Hello Icenowy,
> 
> On 2024-08-12 04:40, Icenowy Zheng wrote:
>> 在 2024-08-12星期一的 04:00 +0200，Dragan Simic写道：
>>> Add thermal trips for the two GPU thermal sensors found in the
>>> Allwinner A64.
>>> There's only one GPU OPP defined since the commit 1428f0c19f9c
>>> ("arm64: dts:
>>> allwinner: a64: Run GPU at 432 MHz"), so defining only the critical
>>> thermal
>>> trips makes sense for the A64's two GPU thermal zones.
>>>
>>> Having these critical thermal trips defined ensures that no hot spots
>>> develop
>>> inside the SoC die that exceed the maximum junction temperature.
>>> That might
>>> have been possible before, although quite unlikely, because the CPU
>>> and GPU
>>> portions of the SoC are packed closely inside the SoC, so the
>>> overheating GPU
>>> would inevitably result in the heat soaking into the CPU portion of
>>> the SoC,
>>> causing the CPU thermal sensor to return high readings and trigger
>>> the CPU
>>> critical thermal trips.  However, it's better not to rely on the heat
>>> soak
>>> and have the critical GPU thermal trips properly defined instead.
>>>
>>> While there, remove a few spotted comments that are rather redundant,
>>> because
>>> it's pretty much obvious what units are used in those places.
>>
>> This should be another individual patch, I think.
> 
> Perhaps, which I already thought about, but it might also be best
> to simply drop the removal of those redundant comments entirely.
> Let's also see what will other people say.
> 
>>> Signed-off-by: Dragan Simic <dsimic@...jaro.org>
>>> ---
>>>  arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi | 22 ++++++++++++++---
>>> -- 
>>>  1 file changed, 16 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
>>> b/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
>>> index e868ca5ae753..bc5d3a2e6c98 100644
>>> --- a/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
>>> +++ b/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
>>> @@ -212,7 +212,6 @@ timer {
>>>
>>>         thermal-zones {
>>>                 cpu_thermal: cpu0-thermal {
>>> -                       /* milliseconds */
>>
>> The unit of a 0 isn't not so obvious I think, so I suggest to keep
>> this.
> 
> Quite frankly, I think it should be obvious to anyone tackling
> the thermal zones and trips.

You can remove also polling-delay-passive and  polling-passive when they 
are equal to zero. If they are absent they will be set to zero by default.

That said, I take the opportunity to spot some inconsistency in this DT 
not related to this change.

1. There is a passive trip point and one cooling device mapped to it. 
With a polling-delay-passive=0, the mitigation will fail

2. There is a second mapping for the hot trip point. That does not make 
sense, it is not possible because there is no mitigation for 'hot' and 
'critical' trip points.


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