linux-kernel - Re: [PATCH] arm64: dts: allwinner: a64: Move CPU OPPs to the SoC dtsi file

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Message-ID: <8a80465aaa4b7dc4c8c15d7a73944cfd@manjaro.org>
Date: Thu, 05 Sep 2024 14:54:03 +0200
From: Dragan Simic <dsimic@...jaro.org>
To: Andre Przywara <andre.przywara@....com>
Cc: Chen-Yu Tsai <wens@...e.org>, linux-sunxi@...ts.linux.dev,
 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
Subject: Re: [PATCH] arm64: dts: allwinner: a64: Move CPU OPPs to the SoC dtsi
 file

On 2024-09-05 14:42, Andre Przywara wrote:
> On Thu, 05 Sep 2024 14:38:53 +0200
> Dragan Simic <dsimic@...jaro.org> wrote:
> 
>> Hello Andre,
>> 
>> On 2024-09-05 14:34, Andre Przywara wrote:
>> > On Thu, 5 Sep 2024 20:26:15 +0800
>> > Chen-Yu Tsai <wens@...e.org> wrote:
>> >
>> >> Hi,
>> >>
>> >> On Thu, Sep 5, 2024 at 8:17 PM Dragan Simic <dsimic@...jaro.org>
>> >> wrote:
>> >> >
>> >> > Hello,
>> >> >
>> >> > Just checking, any further thoughts about this patch?
>> >>
>> >> Sorry, but I feel like it's not really worth the churn. There's not
>> >> really a problem to be solved here. What you are arguing for is more
>> >> about aesthetics, and we could argue that having them separate makes
>> >> it easier to read and turn on/off.
>> >
>> > Yeah, I agree. If a board wants to support OPPs, they just have to
>> > include
>> > a single file and define the CPU regulator, and that's a nice opt-in,
>> > IMHO.
>> > But having this patch would make it quite hard to opt out, I believe.
>> > For
>> > Linux there are probably ways to disable DVFS nevertheless, but I am
>> > not
>> > sure this is true in an OS agnostic pure-DT-only way.
>> 
>> Thanks for your response.  The only thing that still makes me wonder
>> is why would a board want to opt out of DVFS?  Frankly, I'd consider
>> the design of the boards that must keep DVFS disabled broken.
> 
> Yes! Among the boards using Allwinner SoCs there are some, say 
> less-optimal
> designs ;-)

I see, but such boards could simply disable the "cpu0_opp_table" node in
their dts(i) files, for the encapsulated CPU OPPs scenario, and 
everything
would still work and be defined in a clean(er) way.

I mean, if there are some suboptimal designs, perhaps the defaults 
should
be tailored towards the good designs, and the suboptimal designs should 
be
some kind of exceptions.

>> > This could probably be solved, but same as Chen-Yu I don't see any good
>> > enough reason for this patch in the first place.
>> >
>> >> And even though the GPU OPPs are in the dtsi, it's just one OPP acting
>> >> as a default clock rate.