linux-kernel - Re: [PATCH 0/2] Add board-id support for multiple DT selection

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Date: Wed, 14 Feb 2024 14:12:12 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Amrit Anand <quic_amrianan@...cinc.com>, Rob Herring <robh@...nel.org>
Cc: krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
 agross@...nel.org, andersson@...nel.org, konrad.dybcio@...aro.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-msm@...r.kernel.org, kernel@...cinc.com
Subject: Re: [PATCH 0/2] Add board-id support for multiple DT selection

On 14/02/2024 13:56, Amrit Anand wrote:
> On 2/2/2024 10:30 AM, Amrit Anand wrote:
> <snip>
>>> There's a similar issue for EFI boot with how to select an OS installed
>>> DTB[1]. You might not care now, but users may later on (like we have
>>> already with QCom devices with fixed bootloaders). If you do this
>>> board-id route, then no doubt that compatible values won't be specific
>>> enough or have suitable fallbacks to be used. Then EFI boot can't use
>>> compatible either and needs to use this QCom specific logic. It may be a
>>> common property name, but all the types you defined are QCom specific
>>> and the matching logic is pretty much undocumented. I'm not saying we
>>> have to use compatible. There wasn't even agreement to use it for EFI
>>> boot case. This does need to work for multiple vendors and multiple boot
>>> scenarios.
>>>
>> Agree, given so many hardware identifiers Qcom uses to find the DT 
>> based on a best and exact match algorithm, it may not work as is for 
>> other vendors/users outside the scope of Qcom.
>> Since we have none to very limited visibility into complete set of DT 
>> selection identifiers being used by other users or into their 
>> selection algorithms since it is mostly undocumented,
>> designing a perfectly generic solution (one-size-fits-all) could be 
>> far-fetched. The number of board files in Qcom DT selection software 
>> package often reaches over 100 DT files due to multiple SoCs and
>> board types being supported out of a single software package and these 
>> multiple hardware identifiers helps to pick the closest best match DT 
>> within a very large pool of DTs.
>> Not to affect other users/vendors who would be using their own set of 
>> identifiers and an entirely different algorithm for DT selection, 
>> would it make more sense to define these Qcom specific
>> identifiers within Qcom specific bindings (qcom.yaml), along with 
>> detailed documentation on our DT selection algorithm?
> 
> 
> I have written a patch for defining Qcom specific identifiers within 
> Qcom specific bindings (qcom.yaml) along with documentation on DT 
> selection algorithm, would it be okay to send for review?

New ideas and patches in good-faith are always welcomed for review, so
go ahead.

What's still missing here is involvement of other SoC vendors: at least
their maintainers and mailing lists.

Best regards,
Krzysztof