linux-kernel - Re: [PATCH] arm64: dts: rockchip: Add optional GPU OPP voltage ranges to RK356x SoC dtsi

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Date: Sat, 29 Jun 2024 18:22:14 +0200
From: Dragan Simic <dsimic@...jaro.org>
To: Heiko Stübner <heiko@...ech.de>
Cc: linux-rockchip@...ts.infradead.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, Diederik de Haas <didi.debian@...ow.org>,
 Jonas Karlman <jonas@...boo.se>
Subject: Re: [PATCH] arm64: dts: rockchip: Add optional GPU OPP voltage ranges
 to RK356x SoC dtsi

On 2024-06-29 18:18, Heiko Stübner wrote:
> Am Samstag, 29. Juni 2024, 17:39:34 CEST schrieb Dragan Simic:
>> On 2024-06-29 17:25, Dragan Simic wrote:
>> > On 2024-06-29 17:10, Heiko Stübner wrote:
>> >> Am Samstag, 29. Juni 2024, 07:11:24 CEST schrieb Dragan Simic:
>> >>
>> >>> +#ifndef RK356X_GPU_NPU_SHARED_REGULATOR
>> >>
>> >> is there some reason for this duplicating of opps?
>> >>
>> >> The regulator framework should pick the lowest supported voltage
>> >> anyway, so it seems you're just extending them upwards a bit.
>> >>
>> >> So I really don't so why we'd need to sets here.
>> >
>> > The reason is improved strictness.  Having the exact GPU OPP voltages
>> > required for the boards whose GPU regulators can provide those exact
>> > voltages makes it possible to detect misconfigurations much easier,
>> > just like it was the case with the board dts misconfiguration that
>> > resulted in the recent DCDC_REG2 patch. [1]
>> >
>> > If we had GPU OPP voltage ranges in place instead, the aforementioned
>> > issue would probably remain undetected for some time.  It wouldn't be
>> > the end of the world, :) of course, but the resulting increased power
>> > consumption isn't one of the desired outcomes.
>> >
>> > [1]
>> > https://lore.kernel.org/linux-rockchip/e70742ea2df432bf57b3f7de542d81ca22b0da2f.1716225483.git.dsimic@manjaro.org/
>> 
>> On second thought, after seeing that the RK3399 CPU and GPU OPPs
>> already specify voltage ranges, I think it would be better to drop
>> the distinction between the separate strict voltages and the voltage
>> ranges in this patch,
> 
> yes, that was what I was trying to say :-)
> 
> Also it makes the OPPs less cluttered. Also dt is firmware, I do expect
> people to be reasonably knowledgeable if they mess around with their
> boards OPPs ;-) .

Yes, but we still need new regulator/OPP debugging facilities
that should to be used while writing DTs for new boards and while
verifying already existing board DTs. :)

I'll prepare and send the v2 of this patch, and I'll also start
working on the new patch for those debugging facilities.