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 18:18:06 +0200
From: Heiko Stübner <heiko@...ech.de>
To: Dragan Simic <dsimic@...jaro.org>
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

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 ;-) .