Re: [PATCH 2/9] dt-bindings: arm: mediatek: Add MT8186 Tentacruel / Tentacool Chromebooks

[Conor Dooley <conor@kernel.org>]

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On Fri, Oct 13, 2023 at 10:29:25AM -0700, Chen-Yu Tsai wrote:
> On Fri, Oct 13, 2023 at 8:11 AM Conor Dooley <conor@kernel.org> wrote:
> >
> > On Fri, Oct 13, 2023 at 07:02:28AM +0800, Chen-Yu Tsai wrote:
> > > Add entries for MT8186 based Tentacruel / Tentacool Chromebooks. The two
> > > are based on the same board design: the former is a convertible device
> > > with a touchscreen, stylus, and some extra buttons; the latter is a
> > > clamshell device and lacks these additional features.
> > >
> > > The two devices both have two variants. The difference is a second
> > > source touchpad controller that shares the same address as the original,
> > > but is incompatible.
> >
> > > The extra SKU IDs for the Tentacruel devices map to different sensor
> > > components attached to the Embedded Controller. These are not visible
> > > to the main processor.
> >
> > Wha? Given your ordering, is a "google,tentacruel-sku262144" a super-set
> > of "google,tentacruel-sku262145"? If not, this compatible ordering
> > doesn't make sense. I can't tell from your description, and the
> > absence of a
> > items:
> >           - const: google,tentacruel-sku262145
> >           - const: google,tentacruel-sku262146
> >           - const: google,tentacruel-sku262147
> >           - const: google,tentacruel
> >           - const: mediatek,mt8186
> > suggests that there is no google,tentacruel-sku262145
> > device?
> 
> AFAIK all four SKUs exist. And as far as the main processor is concerned,
> they look completely identical, so they should share the same device tree.
> As mentioned in the commit message, the differences are only visible to
> the embedded controller, which fuses the sensor inputs.

Then it makes very little sense to write a binding like this.
If this was just for the 252144 SKU, this would be fine.
For the other SKUs, there is no way to uniquely identify them, as
all four of google,tentacruel-sku262144, google,tentacruel-sku262145,
google,tentacruel-sku262146 and google,tentacruel-sku262147 must be
present.
Given that, why even bother including the SKUs in the first place,
since no information can be derived from them that cannot be derived
from google,tentacruel?
There's something that I am clearly missing here...

Also, why is the order inverted, with the lower SKUs being super-sets of
the higher ones? The Hana one you show below makes a little more sense
in that regard.

> Writing it this way avoids having four identical device tree files.
> 
> We also do this for many other device families, though those cover
> different revisions, such as:
> 
>       - description: Google Hana (Lenovo Chromebook N23 Yoga, C330, 300e,...)
>         items:
>           - const: google,hana-rev6
>           - const: google,hana-rev5
>           - const: google,hana-rev4
>           - const: google,hana-rev3
>           - const: google,hana
>           - const: mediatek,mt8173
> 
> 
> ChenYu
> 
> > Cheers,
> > Conor.
> >
> > >
> > > Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
> > > ---
> > >  .../devicetree/bindings/arm/mediatek.yaml     | 26 +++++++++++++++++++
> > >  1 file changed, 26 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/arm/mediatek.yaml b/Documentation/devicetree/bindings/arm/mediatek.yaml
> > > index 60337b439744..aa7e6734b336 100644
> > > --- a/Documentation/devicetree/bindings/arm/mediatek.yaml
> > > +++ b/Documentation/devicetree/bindings/arm/mediatek.yaml
> > > @@ -206,6 +206,32 @@ properties:
> > >            - enum:
> > >                - mediatek,mt8183-pumpkin
> > >            - const: mediatek,mt8183
> > > +      - description: Google Tentacruel (ASUS Chromebook CM14 Flip CM1402F)
> > > +        items:
> > > +          - const: google,tentacruel-sku262144
> > > +          - const: google,tentacruel-sku262145
> > > +          - const: google,tentacruel-sku262146
> > > +          - const: google,tentacruel-sku262147
> > > +          - const: google,tentacruel
> > > +          - const: mediatek,mt8186
> > > +      - description: Google Tentacruel (ASUS Chromebook CM14 Flip CM1402F)
> > > +        items:
> > > +          - const: google,tentacruel-sku262148
> > > +          - const: google,tentacruel-sku262149
> > > +          - const: google,tentacruel-sku262150
> > > +          - const: google,tentacruel-sku262151
> > > +          - const: google,tentacruel
> > > +          - const: mediatek,mt8186
> > > +      - description: Google Tentacool (ASUS Chromebook CM14 CM1402C)
> > > +        items:
> > > +          - const: google,tentacruel-sku327681
> > > +          - const: google,tentacruel
> > > +          - const: mediatek,mt8186
> > > +      - description: Google Tentacool (ASUS Chromebook CM14 CM1402C)
> > > +        items:
> > > +          - const: google,tentacruel-sku327683
> > > +          - const: google,tentacruel
> > > +          - const: mediatek,mt8186
> > >        - items:
> > >            - enum:
> > >                - mediatek,mt8186-evb
> > > --
> > > 2.42.0.655.g421f12c284-goog
> > >

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