linux-kernel - Re: [PATCH v2 3/9] arm64: dts: bcmbca: update BCM4908 board dts files

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Date:   Wed, 27 Jul 2022 12:39:33 +0200
From:   Rafał Miłecki <rafal@...ecki.pl>
To:     William Zhang <william.zhang@...adcom.com>
Cc:     Rob Herring <robh@...nel.org>,
        Linux ARM List <linux-arm-kernel@...ts.infradead.org>,
        joel.peshkin@...adcom.com, f.fainelli@...il.com,
        Broadcom Kernel List <bcm-kernel-feedback-list@...adcom.com>,
        dan.beygelman@...adcom.com, anand.gore@...adcom.com,
        kursad.oney@...adcom.com, krzysztof.kozlowski@...aro.org,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/9] arm64: dts: bcmbca: update BCM4908 board dts files

On 2022-07-26 03:09, William Zhang wrote:
> On 07/25/2022 04:32 PM, Rob Herring wrote:
>> On Sun, Jul 24, 2022 at 10:53:56PM -0700, William Zhang wrote:
>>> Append "brcm,bcmbca" to compatible strings based on the new bcmbca
>>> binding rule for BCM4908 family based boards. This will break drivers
>>> that use the old compatible string for binding. Fortunately there is 
>>> no
>>> such usage in linux and u-boot.
>> 
>> How does adding an additional compatible break things?
>> In theory when some crazy code tries to match the entire string. But 
>> not
> in linux, u-boot code and hopefully not in other bootloader and Os
> does that. But this does change an existing compatible string so
> Krzysztof suggested to add comment about the breakage in the commit
> message. I can remove this and send v3 if you guys think it is
> necessary.

Krzysztof commented on ABI breakage [1] when you tried removing
"brcm,bcm4908" from the "compatible" list in your patch
[RFC PATCH 3/3] arm64: dts: bcmbca: update bcm4808 board dts file [2]

In this version of your patch you don't remove "brcm,bcm4908" anymore so
this change doesn't break anything. Adding a new "compatible" string
doesn't break things. You can remove that info from the commit message.

[1] 
https://lore.kernel.org/linux-arm-kernel/d93e55fa-3359-2609-aad5-c80eca78f380@linaro.org/
[2] 
https://lore.kernel.org/linux-arm-kernel/20220712021144.7068-4-william.zhang@broadcom.com/