Date:   Thu, 19 May 2022 15:46:53 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh@...nel.org>, Stephen Boyd <sboyd@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Andy Gross <agross@...nel.org>,
        Olof Johansson <olof@...om.net>
Cc:     "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Removal of qcom,board-id and qcom,msm-id

On 19/05/2022 14:53, Krzysztof Kozlowski wrote:
> On 19/05/2022 13:39, Dmitry Baryshkov wrote:
>> On 19/05/2022 13:44, Krzysztof Kozlowski wrote:
>>> Hi,
>>>
>>> There was an old effort of removal of qcom,board-id and qcom,msm-id
>>> properties from Qualcomm SoC-based boards like [1].
>>>
>>> First approach was to document them, which (obviously) was not well
>>> received [2] [3] [4].
>>>
>>> The solution from Stephen was to encode these in the board compatible,
>>> so bootloader can extract that information. That seemed to receive
>>> positive comments, at least from Rob. [5]
>>>
>>> It was 2015... ~7 years later we are still things doing the same way,
>>> still with undocumented properties: qcom,board-id and qcom,msm-id.
>>>
>>>
>>> I would like to revive that topic, but before I start doing something
>>> pointless - any guidance on last patch from Stephen [5]? Was it ok? Some
>>> early NAKs?
>>
>> I do not quite fancy the idea of using extra tools to process dtb files.
>> At this moment it is possible to concatenate several kernel-generated
>> dtb files together. AOSP developers use this to have an image that boots
>> on both RB3 and RB5 boards.
>>
>> I think that changing compat strings only makes sense if Qualcomm would
>> use such compat strings in future. Otherwise we end up in a position
>> where we have custom bootloaders for the RB3/RB5/etc, but the majority
>> of the board requires extra processing steps.
> 
> This was discussed in [2] [3] and [4] (previous links) and did not pass.
> 
> Do you have any new arguments for above objections from Arnd, Olof and
> Rob? I don't think patch will get accepted if previous concerns during
> review are not addressed...

I'm not sure if the patches to the dtbTool have landed or not.
Anyway, as I said, I don't think post-processing the dtb is good way to 
go. It makes extremely hard to check that the dtb, used by the kernel or 
being a part of the boot.img, corresponds to this or that compiled dtb.

> 
>>
>> So, I think, we should drop the unspecified usid aliases, document the
>> board-id/msm-id/pmic-id properties and stick with them.
> 
> The existing properties need anyway documenting, probably as deprecated
> so the schema can pass, because we cannot fix the bootloaders easly.
> 
>> They might be
>> ugly, but they are expected/processed by the majority of devices present
>> in the wild.
> 
> Any change in DTS affects only future devices, so not in the wild...

It affects existing devices that have deployed bootloaders. So far we 
could workaround thus by enforcing a single dtb attached to the kernel 
image. However this doesn't play well for the distro (or AOSP) kernels, 
where we'd like to have multiple dtb image attached.

> 
>>
>>> [1]
>>> https://elixir.bootlin.com/linux/v5.18-rc7/source/arch/arm64/boot/dts/qcom/sdm845-oneplus-fajita.dts#L14
>>>
>>> [2] https://lore.kernel.org/all/7229476.C4So9noUlf@wuerfel/
>>> [3]
>>> https://lore.kernel.org/all/1450371534-10923-20-git-send-email-mtitinger+renesas@baylibre.com/
>>> [4] https://lore.kernel.org/all/20151119153640.GC893@linaro.org/
>>> [5]
>>> https://lore.kernel.org/all/1448062280-15406-1-git-send-email-sboyd@codeaurora.org/


-- 
With best wishes
Dmitry

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