linux-kernel - Re: [PATCH v2 0/2] Add board-id support for multiple DT selection

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Date: Thu, 28 Mar 2024 09:50:16 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Amrit Anand <quic_amrianan@...cinc.com>, robh@...nel.org,
 krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org, agross@...nel.org,
 andersson@...nel.org, konrad.dybcio@...aro.org
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-msm@...r.kernel.org, kernel@...cinc.com, peter.griffin@...aro.org,
 caleb.connolly@...aro.org, linux-riscv@...ts.infradead.org,
 chrome-platform@...ts.linux.dev, linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v2 0/2] Add board-id support for multiple DT selection

On 14/03/2024 13:11, Amrit Anand wrote:
> The software packages are shipped with multiple device tree blobs supporting
> multiple boards. For instance, suppose we have 3 SoC, each with 4 boards supported,
> along with 2 PMIC support for each case which would lead to total of 24 DTB files.
> Along with these configurations, OEMs may also add certain additional board variants.
> Hence, a mechanism is required to pick the correct DTB for the board on which the
> software package is deployed. Introduce a unique property for adding board identifiers
> to device trees. Here, board-id property provides a mechanism for Qualcomm based
> bootloaders to select the appropriate DTB.
> 
> Isn't that what the compatible property is for?
> -----------------------------------------------
> The compatible property can be used for board matching, but requires
> bootloaders and/or firmware to maintain a database of possible strings
> to match against or have complex compatible string parsing and matching.
> Compatible string matching becomes complicated when there are multiple
> versions of the same board. It becomes difficult for the device tree
> selection mechanism to recognize the right DTB to pick, with minor
> differences in compatible strings.
> 
> The solution proposed here is simpler to implement and doesn't require the need
> to update bootloader for every new board.

One of the concerns you got in v1 was: show us second user, so I believe
in your interest is to Cc other platform maintainers which could support
this idea.

Best regards,
Krzysztof