Re: [PATCH v8 1/3] dt-bindings: pwm: Add binding for Allwinner D1/T113-S3/R329 PWM controller

[Conor Dooley]

On Thu, Feb 01, 2024 at 05:48:51PM +0000, Andre Przywara wrote:
> On Wed, 31 Jan 2024 21:22:06 +0000
> Conor Dooley <conor@xxxxxxxxxx> wrote:
> 
> Hi,
> 
> > On Wed, Jan 31, 2024 at 02:52:44PM +0000, Andre Przywara wrote:
> > > On Wed, 31 Jan 2024 15:59:14 +0300
> > > Aleksandr Shubin <privatesub2@xxxxxxxxx> wrote:
> > > 
> > > Hi,
> > >   
> > > > Allwinner's D1, T113-S3 and R329 SoCs have a new pwm
> > > > controller witch is different from the previous pwm-sun4i.
> > > > 
> > > > The D1 and T113 are identical in terms of peripherals,
> > > > they differ only in the architecture of the CPU core, and
> > > > even share the majority of their DT. Because of that,
> > > > using the same compatible makes sense.
> > > > The R329 is a different SoC though, and should have
> > > > a different compatible string added, especially as there
> > > > is a difference in the number of channels.
> > > > 
> > > > D1 and T113s SoCs have one PWM controller with 8 channels.
> > > > R329 SoC has two PWM controllers in both power domains, one of
> > > > them has 9 channels (CPUX one) and the other has 6 (CPUS one).
> > > > 
> > > > Add a device tree binding for them.
> > > > 
> > > > Signed-off-by: Aleksandr Shubin <privatesub2@xxxxxxxxx>
> > > > Reviewed-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
> > > > ---
> > > >  .../bindings/pwm/allwinner,sun20i-pwm.yaml    | 88 +++++++++++++++++++
> > > >  1 file changed, 88 insertions(+)
> > > >  create mode 100644 Documentation/devicetree/bindings/pwm/allwinner,sun20i-pwm.yaml
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/pwm/allwinner,sun20i-pwm.yaml b/Documentation/devicetree/bindings/pwm/allwinner,sun20i-pwm.yaml
> > > > new file mode 100644
> > > > index 000000000000..716f75776006
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/pwm/allwinner,sun20i-pwm.yaml
> > > > @@ -0,0 +1,88 @@
> > > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > > +%YAML 1.2
> > > > +---
> > > > +$id: http://devicetree.org/schemas/pwm/allwinner,sun20i-pwm.yaml#
> > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > +
> > > > +title: Allwinner D1, T113-S3 and R329 PWM
> > > > +
> > > > +maintainers:
> > > > +  - Aleksandr Shubin <privatesub2@xxxxxxxxx>
> > > > +  - Brandon Cheo Fusi <fusibrandon13@xxxxxxxxx>
> > > > +
> > > > +properties:
> > > > +  compatible:
> > > > +    oneOf:
> > > > +      - const: allwinner,sun20i-d1-pwm
> > > > +      - items:
> > > > +          - const: allwinner,sun20i-r329-pwm
> > > > +          - const: allwinner,sun20i-d1-pwm
> > > > +
> > > > +  reg:
> > > > +    maxItems: 1
> > > > +
> > > > +  "#pwm-cells":
> > > > +    const: 3
> > > > +
> > > > +  clocks:
> > > > +    items:
> > > > +      - description: Bus clock
> > > > +      - description: 24 MHz oscillator
> > > > +      - description: APB0 clock
> > > > +
> > > > +  clock-names:
> > > > +    items:
> > > > +      - const: bus
> > > > +      - const: hosc
> > > > +      - const: apb0
> > > > +
> > > > +  resets:
> > > > +    maxItems: 1
> > > > +
> > > > +  allwinner,pwm-channels:
> > > > +    $ref: /schemas/types.yaml#/definitions/uint32
> > > > +    description: The number of PWM channels configured for this instance
> > > > +    enum: [6, 9]
> > > > +
> > > > +allOf:
> > > > +  - $ref: pwm.yaml#
> > > > +
> > > > +  - if:
> > > > +      properties:
> > > > +        compatible:
> > > > +          contains:
> > > > +            const: allwinner,sun20i-r329-pwm
> > > > +
> > > > +    then:
> > > > +      required:
> > > > +        - allwinner,pwm-channels
> > > > +
> > > > +    else:
> > > > +      properties:
> > > > +        allwinner,pwm-channels: false  
> > > 
> > > Do we really need to be that strict?
> > > If something compatible to D1 pops up in the future, just with a different
> > > number of channels, we would need a new compatible string.  
> > 
> > Well, you would want to have a soc specific compatible anyway then,
> > right?
> 
> So the idea would be to add any new (specific) compatible string to that
> list then, when we add them?
> I guess this would work, but strictly speaking any current driver would
> then only need to check this property for the R329 type? The Linux
> driver proposed in the next patch *always* honours the
> allwinner,pwm-channels property, which is IMHO the right way to implement
> this. And that's why I think the binding should reflect that, and not
> explicitly *forbid* the property for every one other than R329 (atm).
> 
> With the current Linux driver, a potential new SoC using:
> 	"allwinner,sun20i-d2-pwm", "allwinner,sun20i-d1-pwm";
> 	allwinner,pwm-channels = <6>;
> would work without driver changes. A driver strictly written to this
> binding here might not, though, as it would be free to ignore the
> pwm-channels property.
> 
> Does that make sense? So to encourage future compatibility, can we drop
> the "else" branch?

Oh true, I see what you mean now with the example you gave. I wouldn't
respin for this alone, since the else branch could be dropped when
another user showed up given the driver doesn't restrict things.
I'm okay with your suggestion though.

Cheer,
Conor.

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