Re: [PATCH 1/4] dt-bindings: remoteproc: qcom: wcnss: Add WCN3680B compatible

[Stephan Gerhold <stephan@gerhold.net>]

On Mon, Oct 16, 2023 at 03:16:14PM +0200, Loic Poulain wrote:
> On Mon, 16 Oct 2023 at 07:35, Krzysztof Kozlowski
> <krzysztof.kozlowski@linaro.org> wrote:
> >
> > On 15/10/2023 22:03, Luca Weiss wrote:
> > > Add a compatible for the iris subnode in the WCNSS PIL.
> > >
> > > Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
> > > ---
> > >  Documentation/devicetree/bindings/remoteproc/qcom,wcnss-pil.yaml | 1 +
> > >  1 file changed, 1 insertion(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/remoteproc/qcom,wcnss-pil.yaml b/Documentation/devicetree/bindings/remoteproc/qcom,wcnss-pil.yaml
> > > index 45eb42bd3c2c..0e5e0b7a0610 100644
> > > --- a/Documentation/devicetree/bindings/remoteproc/qcom,wcnss-pil.yaml
> > > +++ b/Documentation/devicetree/bindings/remoteproc/qcom,wcnss-pil.yaml
> > > @@ -111,6 +111,7 @@ properties:
> > >            - qcom,wcn3660
> > >            - qcom,wcn3660b
> > >            - qcom,wcn3680
> > > +          - qcom,wcn3680b
> >
> > Looks like this should be made as compatible with qcom,wcn3680 (so with
> > fallback).
> 
> Yes, agree, let's do a regular fallback as there is nothing 'b'
> specific in the driver:
> `compatible = "qcom,wcn3680b", "qcom,wcn3680";`
> 
> And yes, we should also have done that for qcom,wcn3660b...
> 

I don't think this would have worked properly for qcom,wcn3660b:

 - It's not compatible with "qcom,wcn3660", because they have different
   regulator voltage requirements. wcn3660(a?) needs vddpa with
   2.9-3.0V, but wcn3660b needs 3.3V. That's why wcn3660b uses the
   wcn3680_data in qcom_wcnss.iris.c. Otherwise if you would run an
   older kernel that knows "qcom,wcn3660" but not "qcom,wcn3660b" it
   would apply the wrong voltage.

 - It's not compatible with "qcom,wcn3680" either because that is used
   as indication if 802.11ac is supported (wcn3660b doesn't).

The main question here is: What does the current "qcom,wcn3680"
compatible actually represent? It's defined with vddpa = 3.3V in the
driver, which would suggest that:

 1. It's actually meant to represent WCN3680B, which needs 3.3V vddpa
    like WCN3660B, or

 2. WCN3680(A?) has different requirements than WCN3660(A?) and also
    needs 3.3V vddpa. But then what is the difference between
    WCN3680(A?) and WCN3680B? Is there even a variant without ...B?

There is public documentation for WCN3660B and WCN3680B but the non-B
variants are shrouded in mystery.

Thanks,
Stephan