linux-kernel - Re: Removal of qcom,board-id and qcom,msm-id

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Date:   Mon, 23 May 2022 11:11:29 +0530
From:   Amit Pundir <amit.pundir@...aro.org>
To:     krzysztof.kozlowski@...aro.org,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     agross@...nel.org, arnd@...db.de, bjorn.andersson@...aro.org,
        devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, olof@...om.net, robh@...nel.org,
        sboyd@...nel.org, Konrad Dybcio <konrad.dybcio@...ainline.org>
Subject: Re: Removal of qcom,board-id and qcom,msm-id

On Mon, 23 May 2022 at 01:22, Konrad Dybcio
<konrad.dybcio@...ainline.org> wrote:
>
> Hi,
>
> removing these properties will not bring almost any benefit (other than making
> some checks happy any saving some <200 LoC) and will make the lives of almost
> all people doing independent development for linux-on-msm harder. There are
> almost unironically like 3 people outside Linaro and QUIC who have
> non-vendor-fused development boards AND the sources to rebuild the
> bootloader on their own. Making it harder to boot is only going to
> discourage people from developing on these devices, which is already not
> that pleasant, especially with newer platforms where you have to fight with
> the oh-so-bright ideas of Android boot chain..
>
> This only concerns devices released before sm8350, as the new ones will not
> even boot with these properties present (or at least SONY Sagami, but I
> doubt it's an isolated case), so other than completing support for older
> devices, it won't be an issue going forward, anyway. But there are give
> or take 50 locked down devices in mainline right now, and many more waiting
> to be upstreamed in various downstream close-to-mainline trees that should
> not be disregarded just because Qualcomm is far from the best at making
> their BSP software stack clean.
>
> One solution is to chainload another, (n+1)-stage bootloader, but this is
> not ideal, as:
>
> 1) the stock bootloader can boot Linux just fine on most devices (except
> for single exceptions, where beloved OEMs didn't implement arm64 booting or
> something)
>
> 2) the boot chain on MSM is already 3- or 4- stage and adding to that will
> only create an unnecessary mess
>
> 3) the job of kernel people is not to break userspace. If the
> device can not even exit bootloader after a kernel upgrade, it's a big
> failure.
>
> If you *really really really* want these either gone or documented, we can
> for example use them in the SOCID driver, read the values from DTB and
> compare against what SMEM has to say and for example print a warning when
> there are inconsistencies or use it as a fallback when it fails for any
> reason, such as using a newer SoC on an older kernel, without updates
> for SOCID read (which are sometimes necessary, which was the case for 8450
> recently, iirc).
>
> My stance is to just leave them as is, as moving them anywhere, or removing
> them at all will cause unnecessary mess and waste time that could have been
> spent on more glaring issues..

I couldn't have put it better myself. I suggest we document these
properties, if that is the blocker, and keep them. A lot has changed
in the last 7 years, we now have dozens of devices booting upstream
kernel using these properties.

And fwiw, I have not used dtbTool before, if anything I'd rather
explore dtb overlays.

Regards,
Amit Pundir

>
> Konrad