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

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Message-ID: <20240905142054.58194beb@donnerap.manchester.arm.com>
Date: Thu, 5 Sep 2024 14:20:54 +0100
From: Andre Przywara <andre.przywara@....com>
To: Dragan Simic <dsimic@...jaro.org>
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 Thu, 05 Sep 2024 14:54:03 +0200
Dragan Simic <dsimic@...jaro.org> wrote:

> 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 agree, and I was already about to suggest this as a reply to your initial
post, but I think I tried that, and IIRC this doesn't work: the "status"
property is not honoured for this node.
But please double check that.

Cheers,
Andre

> 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.