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Date:   Wed, 27 Jul 2022 12:39:33 +0200
From:   =?UTF-8?Q?Rafa=C5=82_Mi=C5=82ecki?= <rafal@milecki.pl>
To:     William Zhang <william.zhang@broadcom.com>
Cc:     Rob Herring <robh@kernel.org>,
        Linux ARM List <linux-arm-kernel@lists.infradead.org>,
        joel.peshkin@broadcom.com, f.fainelli@gmail.com,
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        dan.beygelman@broadcom.com, anand.gore@broadcom.com,
        kursad.oney@broadcom.com, krzysztof.kozlowski@linaro.org,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/9] arm64: dts: bcmbca: update BCM4908 board dts files
In-Reply-To: <1004391f-fb6c-5f84-de28-8f76dc3471e5@broadcom.com>
References: <20220725055402.6013-1-william.zhang@broadcom.com>
 <20220725055402.6013-4-william.zhang@broadcom.com>
 <20220725233238.GA2960972-robh@kernel.org>
 <1004391f-fb6c-5f84-de28-8f76dc3471e5@broadcom.com>
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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/