linux-kernel - Re: [PATCH 1/2] dt-bindings: arm: qcom: document zoglin board

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Date:   Wed, 27 Jul 2022 16:11:50 -0600
From:   Rob Herring <robh@...nel.org>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Bob Moragues <moragues@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Bob Moragues <moragues@...gle.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Stephen Boyd <sboyd@...eaurora.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH 1/2] dt-bindings: arm: qcom: document zoglin board

On Wed, Jul 27, 2022 at 3:59 PM Doug Anderson <dianders@...omium.org> wrote:
>
> Hi,
>
> On Wed, Jul 27, 2022 at 12:43 PM Rob Herring <robh@...nel.org> wrote:
> >
> > On Wed, Jul 27, 2022 at 11:40 AM Doug Anderson <dianders@...omium.org> wrote:
> > >
> > > Hi,
> > >
> > > On Wed, Jul 27, 2022 at 9:03 AM Rob Herring <robh@...nel.org> wrote:
> > > >
> > > > On Tue, Jul 26, 2022 at 09:24:31PM -0700, Bob Moragues wrote:
> > > > > Zoglin is a Hoglin Chromebook with SPI Flash reduced from 64MB to 8MB.
> > > > > Zoglin is identical to Hoglin except for the SPI Flash.
> > > > > The actual SPI Flash is dynamically probed at and not specified in DTS.
> > > > >
> > > > > Signed-off-by: Bob Moragues <moragues@...omium.org>
> > > > >
> > > > > Signed-off-by: Bob Moragues <moragues@...gle.com>
> > > > > ---
> > > > >
> > > > >  Documentation/devicetree/bindings/arm/qcom.yaml | 1 +
> > > > >  1 file changed, 1 insertion(+)
> > > > >
> > > > > diff --git a/Documentation/devicetree/bindings/arm/qcom.yaml b/Documentation/devicetree/bindings/arm/qcom.yaml
> > > > > index 581485392404..63091df3cbb3 100644
> > > > > --- a/Documentation/devicetree/bindings/arm/qcom.yaml
> > > > > +++ b/Documentation/devicetree/bindings/arm/qcom.yaml
> > > > > @@ -475,6 +475,7 @@ properties:
> > > > >
> > > > >        - description: Qualcomm Technologies, Inc. sc7280 CRD platform (newest rev)
> > > > >          items:
> > > > > +          - const: google,zoglin
> > > > >            - const: google,hoglin
> > > > >            - const: qcom,sc7280
> > > >
> > > > Is just "google,hoglin", "qcom,sc7280" no longer valid? If it is valid,
> > > > you need another entry.
> > >
> > > If it makes people happy to have another entry then it wouldn't hurt,
> > > but it has no long term benefit and I would recommend against it. The
> > > next patch in this series changes the existing "hoglin" device tree to
> > > have all 3 compatible strings and thus when both patches land then
> > > make dtbs_check will pass. I assume that is the only goal of
> > > documenting these boards here. Certainly if you had a device tree that
> > > had only "google,zoglin" it would boot fine on zoglin devices and if
> > > you had a device tree that had only "google,hoglin" it would boot fine
> > > on hoglin device. This is true of all of the entries for Chromebooks
> > > that have multiple compatible entries.
> >
> > Why even add the entry? If it is just a different SPI flash, you can
> > tell that from the SPI flash compatible or device ID.
>
> Yeah, it's really unfortunate. :( The issue is a limitation in the
> ChromeOS bootloader infrastructure. The ChromeOS build infrastructure
> cannot handle something that it considers the same "board" as having
> different SPI flash sizes. This is because the infrastructure always
> requires that the bootloader "image" be the exact same size as the SPI
> flash and it assumes a universal firmware (single image) per board.
> It's unfortunately not very flexible but normally for a given board
> the SPI flash size is chosen at the start and never changed. The CRD
> board was an exception here. Though it's not beautiful, this means
> that the firmware considers this as a different board and looks for a
> different compatible string on the kernel command line.

Okay, I guess...

Acked-by: Rob Herring <robh@...nel.org>