linux-kernel - Re: [PATCH 0/6] i2c-imx-lpi2c: add IPG clock

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Message-ID: <039566a7-5c65-b2d8-7b45-c616863cb292@linaro.org>
Date:   Tue, 16 Aug 2022 09:01:13 +0300
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Peng Fan <peng.fan@....com>,
        "Peng Fan (OSS)" <peng.fan@....nxp.com>,
        Aisheng Dong <aisheng.dong@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>
Cc:     "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        dl-linux-imx <linux-imx@....com>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Clark Wang <xiaoning.wang@....com>
Subject: Re: [PATCH 0/6] i2c-imx-lpi2c: add IPG clock

On 15/08/2022 03:52, Peng Fan wrote:
> Hi Krzysztof,
> 
>> Subject: Re: [PATCH 0/6] i2c-imx-lpi2c: add IPG clock
>>
>> On 12/08/2022 07:34, Peng Fan (OSS) wrote:
>>> From: Peng Fan <peng.fan@....com>
>>>
>>> The i.MX LPI2C needs PER and IPG clock, not just PER or IPG clock.
>>> This patch is to enable both PER and IPG clock for imx-i2c-lpi2c.
>>
>> This patchset breaks the ABI and is not bisectable. The justification is very
>> limited (one sentence), so not really enough.
> 
> ARM32 i.MX7ULP and ARM64 i.MX8QXP/i.MX8ULP all need to use two
> clocks, PER and IPG. But current dt-bindings and dts, use one clock.
> 
> This patchset includes dts changes patch 4 and patch 5.
> Patch 6 is to update driver use two clocks.
> 
> I think the patch order in this patchset would not break git bisect, it
> just break ABI. But I not find good way how could not break ABI,
> because only use one clock is wrong whether in dt-bindings or dtbs.

Driver changes always go via separate branch than DTS, so your patch
breaks git bisect. I already pointed it out in other patch. This is not
really acceptable. Breaking ABI is another problem which could be
justified with your explanation in other cases... but not in this one,
since it is easy to make it backwards compatible,

> Should I use a fixes tag to dt-bindings, then break ABI is allowed?

No. For such patch ABI break is also not allowed in that case. Just make
the driver backwards compatible and both problems - non bisectability
and ABI break - go away.

Best regards,
Krzysztof