Date:   Mon, 23 May 2022 15:13:07 -0700
From:   Trilok Soni <quic_tsoni@...cinc.com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
CC:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        <agross@...nel.org>, <arnd@...db.de>, <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

Hi Bjorn,

On 5/23/2022 2:34 PM, Bjorn Andersson wrote:
> On Mon 23 May 11:41 CDT 2022, Trilok Soni wrote:
> 
>> Hello Krzysztof,
>>
>> On 5/23/2022 5:14 AM, Krzysztof Kozlowski wrote:
>>> 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/
>>
>>
>> The link above is from 2015. Lot has changed downstream. Most of what was
>> mentioned by Konrad is right. Application bootloader acts on picking on
>> platform DTBO based on the platform ID plus some combinations like PMIC etc;
>> These platform DTBOs gets overlay on top of SOC DTB by the Application
>> bootloader.
>>
>> We have moved to DTBO for all the latest targets, but I can understand that
>> some old targets at upstream could be using the very old approaches.
>>
>> Downstream all of the platforms including the DTBO files will need board-id
>> and msm-id since we also do the compile time stitching of dtb + dtbo and
>> dtbo + dtbo to generate the proper SOC DTB and PLATFORM DTBOs which gets
>> flashed in the DTBO partition and follows the Android boot requirements.
>> Application bootloader then picks the right Platform DTBO as mentioned above
>> w/ the right SOC DTB. It gets more complicated w/ GKI new requirements every
>> year (better for GKI, may not be better for upstream kernel + downstream
>> bootloader combination).
>>
> 
> FWIW, this doesn't fit with the upstream model at all. In particular the
> DTBO that comes with the devices are not compatible with any upstream
> DTB.
> 
> As such, the first step to run an upstream DTB+kernel is to zero out the
> dtbo partitions.
> 
> 
> With the DTBO cleared, most devices (all Qualcomm reference devices) can
> be booted with the dtb appended to the Image.gz, without the
> qcom,{board,msm}-id. As such I would say things are working okay
> currently.
> 

Thanks. Yup, I know things are working fine right now. May be we can 
look at changing the downstream bootloader so that you don't need to 
erase the DTBO partition for reference/unlocked devices. No promise, but 
it will make easy for anyone do the upstream development on the 
reference devices.

---Trilok Soni

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