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

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Message-ID: <DU0PR04MB9417EF15DD50EC51B4FBBCFF886B9@DU0PR04MB9417.eurprd04.prod.outlook.com>
Date:   Tue, 16 Aug 2022 08:43:54 +0000
From:   Peng Fan <peng.fan@....com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        "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

Hi Krzysztof,

> 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.

One more point that I am not very clear about  
"non bisectability and ABI break "

ABI, I suppose you mean dt-binding, right?
The I2C bindings and dts update will go through different tree, I think. So
dtbs_check may fail considering the PR merge order.

Thanks,
Peng.

> 
> Best regards,
> Krzysztof