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

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Date:   Sat, 14 Oct 2023 14:40:26 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Chen-Yu Tsai <wenst@...omium.org>
Cc:     Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/9] dt-bindings: arm: mediatek: Add MT8186 Tentacruel /
 Tentacool Chromebooks

On Fri, Oct 13, 2023 at 11:19:16AM -0700, Chen-Yu Tsai wrote:
> On Fri, Oct 13, 2023 at 10:55 AM Conor Dooley <conor@...nel.org> wrote:
> >
> > 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@...nel.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...
> 
> There are incompatible variants of google,tentacruel. This is why this
> patch has four google,tentacruel based entries. Of them, two are Tentacool,
> which are clamshell laptops, and two of them are Tentacruel, which are
> convertibles.
> 
> Within each group there are two variants: the second variant swaps out
> the I2C touchpad controller. These two controllers use the same I2C
> address but use different compatible strings, so it's not possible to
> have them coexist within the same device tree file like we do for many
> other second source components.
> 
> So the relationship looks like the following:
> 
> google,tentacruel --- Tentacruel --- google,tentacruel-sku26214[4567]
>                    |              |
>                    |              -- google,tentacruel-sku2621{48,49,50,51}
>                    |
>                    -- Tentacool ---- google,tentacruel-sku327681
>                                  |
>                                  --- google,tentacruel-sku327683
> 
> Also, the devices themselves only know their own SKU ID. The firmware
> will generate a list of compatible strings like:
> 
>   google,tentacruel-rev4-sku262144
>   google,tentacruel-rev4
>   google,tentacruel-sku262144
>   google,tentacruel
> 
> and try to find a match in the kernel FIT image. The method we currently
> use is to include all the applicable board compatible strings.

Then it seems like what you need is something like
oneOf:
  - items:
      - const: google,tentacruel-sku262144
      - const: google,tentacruel
      - const: mediatek,mt8186
  - items:
      - enum:
          - google,tentacruel-sku262145
          - google,tentacruel-sku262146
          - google,tentacruel-sku262147
      - const: google,tentacruel-sku262144
      - const: google,tentacruel
      - const: mediatek,mt8186

What you have at the moment just seems like a hack because you want to
stuff all of these compatible strings into a single dts.

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