linux-kernel - Re: [PATCH v1 2/4] arm64: dts: qcom: sc7280: Add 'piglin' to the crd-r3 compatible strings

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Date:   Tue, 22 Mar 2022 09:46:19 +0530
From:   Rajendra Nayak <quic_rjendra@...cinc.com>
To:     Doug Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>
CC:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 2/4] arm64: dts: qcom: sc7280: Add 'piglin' to the
 crd-r3 compatible strings


On 3/21/2022 11:30 PM, Doug Anderson wrote:
> "Hi,
> 
> On Mon, Mar 21, 2022 at 8:14 AM Matthias Kaehlcke <mka@...omium.org> wrote:
>>
>> On Mon, Mar 21, 2022 at 11:14:56AM +0530, Rajendra Nayak wrote:
>>>
>>> On 3/17/2022 5:58 AM, Matthias Kaehlcke wrote:
>>>> With newer bootloader versions the crd-r3 (aka CRD 1.0 and 2.0) is
>>>> identified as a 'piglin' board (like the IDP2 board), instead of 'hoglin'
>>>> Add the compatible strings 'google,piglin-rev{3,4}'. The hoglin entries
>>>> are kept to make sure the board keeps booting with older bootloader
>>>> versions.
>>>
>>> The older bootloaders really look for the google,hoglin-rev3/google,hoglin-rev4
>>> compatibles or just google,hoglin? If its just google,hoglin, won;t it pick the
>>> crd-rev5+ dtb now?
>>
>> They look for the -revN compatible, I confirmed that on my CRD 2.0.
> 
> Thanks for confirming Matthias! I'll also note that, in general, these
> "google,board-revX" type compatible strings are all programmatically
> generated. You can see at:
> 
> https://chromium.googlesource.com/chromiumos/platform/depthcharge/+/refs/heads/main/src/boot/fit.c#70
> 
> ...and whenever it's using this normal logic then it has a standard
> fallback mechanism in place. On a random board in front of me
> depthcharge prints out:
> 
> Compat preference: google,lazor-rev3-sku0 google,lazor-rev3
> google,lazor-sku0 google,lazor
> 
> So it'll first try the very specific verison with rev and sku. Then
> just by rev. Then just by sku. ...and if none of those match it'll
> pick a device tree that has neither. The "newest" device tree always
> has no revision number specified and that way if software doesn't
> change but the revision bumps then we have no problem. We only add the
> revision info for old boards.

Thanks Matthias/Doug for the clarification,

Reviewed-by: Rajendra Nayak <quic_rjendra@...cinc.com>

> 
> There are a few cases where we add special compatible strings and
> these don't match on board/rev. This is fairly uncommon, though. You
> might be aware of the special case of adding "qcom,sc7180-idp"
> (without rev/sku matching) for "bubs". See:
> 
> https://chromium.googlesource.com/chromiumos/platform/depthcharge/+/refs/heads/main/src/board/trogdor/board.c#136
> 
> 
> -Doug