Date:   Mon, 23 May 2022 14:14:47 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...ainline.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
Subject: Re: Removal of qcom,board-id and qcom,msm-id

On 23/05/2022 14:02, Konrad Dybcio wrote:
> 
> On 23/05/2022 09:21, Krzysztof Kozlowski wrote:
>> On 22/05/2022 21:51, Konrad Dybcio 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.
>> I actually wonder why do you need these properties for community work on
>> such boards? You ship kernel with one concatenated DTB and the
>> bootloader does not need the board-id/msm-id fields, doesn't it?
> 
> If that were the case, I would have never complained about this! It's 
> the bootloader itself that needs it, you can see it in a "Best match 
> [blah blah] 258/0x1000/...." log line, where it walks through the 
> appended (or otherwise compiled into the boot.img) DTBs and looks for 
> matches for the burnt-in msm-, board- and (on newer-older platforms) 
> pmic-id. If it cannot find these, it refuses to boot with an Android 
> Verified Boot red state and you get a not-so-nice "Your device has been 
> unlocked and the boot image is not working" or something like this on 
> your screen.
> 
> 
>>
>> Not mentioning that in the past bootloader was actually not using these
>> properties at all, because it was the dtbTool who was parsing them.
> 
> Not sure when that was the case, maybe with very old arm32 bootloaders 
> in the times before I did development on Qualcomm devices.
> 
> 
>>   So
>> in any case either your device works fine without these properties or
>> you have to use dtbTool, right?
> 
> To the best of my idea, wrong :( Unless the vendor modified the LK/XBL 
> code on their own, it looks for a "best match" (but if it's not a 
> precise match, it won't even bother trying to boot, just fyi..), meaning 
> it tries to go through a list of SoC ID and revision pairs (msm-id), 
> board IDs (board-id) and PMIC id+rev pairs (pmic-id) and if no match is 
> found, it doesn't even exit the bootloader and says something like "no 
> dtbs found".

This would mean that dtbTool as described in the actual patch [1] is not
used and bootloader ignores the table. If that's the case, the commit
and requirement of such complex board-foundry-pmic-compatibles should be
dropped. So I am getting now to what Dmitry said...

[1]
https://lore.kernel.org/all/1448062280-15406-2-git-send-email-sboyd@codeaurora.org/


Best regards,
Krzysztof

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