linux-kernel - Re: [PATCH 1/4] dt-bindings: arm: qcom: Document qcom,sc7280-crd board

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Message-ID: <YZ0AZQDB6VPUAt8s@google.com>
Date:   Tue, 23 Nov 2021 06:53:25 -0800
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Rajendra Nayak <rnayak@...eaurora.org>
Cc:     agross@...nel.org, bjorn.andersson@...aro.org, robh+dt@...nel.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, sboyd@...eaurora.org,
        dianders@...omium.org, kgodara@...eaurora.org
Subject: Re: [PATCH 1/4] dt-bindings: arm: qcom: Document qcom,sc7280-crd
 board

On Tue, Nov 23, 2021 at 12:30:10PM +0530, Rajendra Nayak wrote:
> Document the qcom,sc7280-crd board based off sc7280 SoC,
> The board is also known as hoglin in the Chrome OS builds,
> and given there would be multiple (at least one more) rev
> of this board document the google,hoglin-rev0 compatible as well.
> 
> Signed-off-by: Rajendra Nayak <rnayak@...eaurora.org>
> ---
>  Documentation/devicetree/bindings/arm/qcom.yaml | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/arm/qcom.yaml b/Documentation/devicetree/bindings/arm/qcom.yaml
> index c8808e0..2abfd28 100644
> --- a/Documentation/devicetree/bindings/arm/qcom.yaml
> +++ b/Documentation/devicetree/bindings/arm/qcom.yaml
> @@ -203,6 +203,8 @@ properties:
>            - enum:
>                - qcom,sc7280-idp
>                - qcom,sc7280-idp2
> +              - qcom,sc7280-crd
> +              - google,hoglin-rev0

I think we also want the generic 'google,hoglin' compatible string, analogous to
for example 'google,lazor' and 'google,lazor-revN'. For lazor there are no
explicit compatible entries for rev3 and above, there were no DT relevant
hardware changes for rev > 3, hence the 'google,lazor' compatible string is
used, without the need to modify the DT for each new HW revision.

Also on my CRD the bootloader thinks it is running on a rev4:

  Compat preference: google,hoglin-rev4 google,hoglin

The board still boots thanks to the 'google,hoglin' entry in my device tree,
but it seems you need to add more revN entries, or start with rev4 if you
don't really care about supporting older revisions. In the later case you
coul only have 'google,hoglin' for now, and add 'rev4' when you add support
for the next revision (supposing it has DT relevant hardware changes). The
sc7180-trogdor boards can serve as an example on how to deal with board
revisions.