linux-kernel - Re: [PATCH v3 1/2] dt-bindings: regulator: st,stm32mp1-pwr-reg: add compatible for STM32MP13

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Date: Tue, 14 May 2024 21:08:38 +0100
From: Conor Dooley <conor@...nel.org>
To: Patrick DELAUNAY <patrick.delaunay@...s.st.com>
Cc: Marek Vasut <marex@...x.de>,
	Alexandre TORGUE <alexandre.torgue@...s.st.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Pascal Paillet <p.paillet@...s.st.com>, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH v3 1/2] dt-bindings: regulator: st,stm32mp1-pwr-reg: add
 compatible for STM32MP13

On Mon, May 13, 2024 at 08:02:21PM +0200, Patrick DELAUNAY wrote:
> Hi,
> 
> On 5/13/24 17:16, Conor Dooley wrote:
> > On Mon, May 13, 2024 at 04:34:20PM +0200, Marek Vasut wrote:
> > > On 5/13/24 11:56 AM, Patrick Delaunay wrote:
> > > > Add new compatible "st,stm32mp13-pwr-reg" for STM32MP13 SoC family.
> > > > 
> > > > Signed-off-by: Patrick Delaunay <patrick.delaunay@...s.st.com>
> > > > ---
> > > > 
> > > > Changes in v3:
> > > > - Replace oneOf/const by enum; solve the V2 issues for dt_binding_check
> > > > 
> > > > Changes in v2:
> > > > - update for Rob review, only add compatible for STM32MP13 family
> > > > 
> > > >    .../devicetree/bindings/regulator/st,stm32mp1-pwr-reg.yaml    | 4 +++-
> > > >    1 file changed, 3 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/regulator/st,stm32mp1-pwr-reg.yaml b/Documentation/devicetree/bindings/regulator/st,stm32mp1-pwr-reg.yaml
> > > > index c9586d277f41..c766f0a15a31 100644
> > > > --- a/Documentation/devicetree/bindings/regulator/st,stm32mp1-pwr-reg.yaml
> > > > +++ b/Documentation/devicetree/bindings/regulator/st,stm32mp1-pwr-reg.yaml
> > > > @@ -11,7 +11,9 @@ maintainers:
> > > >    properties:
> > > >      compatible:
> > > > -    const: st,stm32mp1,pwr-reg
> > > > +    enum:
> > > > +      - st,stm32mp1,pwr-reg
> > > > +      - st,stm32mp13-pwr-reg
> > > Should the st,stm32mp1,pwr-reg be treated as fallback compatible for
> > > st,stm32mp13-pwr-reg or not ?
> > > 
> > > In other words, should the DT contain:
> > > compatible = "st,stm32mp13-pwr-reg", "st,stm32mp1,pwr-reg";
> > > or
> > > compatible = "st,stm32mp13-pwr-reg";
> > > ? Which one is preferable ?
> > > 
> > > I think the former one, since the MP13 PWR block could also be operated by
> > > older MP1(5) PWR block driver(s) without any adverse effects, except the SD
> > > IO domain configuration won't be available, right ?
> > Aye, the fallback sounds like what should be being used here, especially
> > if another user of the DT might not need to implement the extra domain.
> 
> 
> Yes it is the the only difference but I think that type of fallback is no
> more recommended for different device and
> 
> the PWR device on STM32MP13 and on STM32MP15 are different.
> 
> 
> The other user of the non-secure device tree don't use the yet the PWR
> driver for STM32MP13,
> 
> so for me the fallback is not needed for non secure world (Linux/U-Boot).
> 
> 
> So I prefer to introduce a new compatible in Linux kernel before the
> STM32MP13 PWR node is really used  to avoid ABI break in futur.

How is it going to break an ABI? If the mp13 implements a functional
subset of what the mp1 does, then that's what fallback compatibles
are intended for. Marek's mail suggests that this is the case, and
therefore a fallback should be used.

If code written for the mp1 would not work on the mp13, then a fallback
should not be used.

Neither I nor Marek are saying that a new compatible should not be
created, in case you misunderstood that. This only affects the binding
patch, and your driver etc are free to use the mp13 compatible.

Thanks,
Conor.

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