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

From: Peng Fan <peng.fan@nxp.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
	"Peng Fan (OSS)" <peng.fan@oss.nxp.com>,
	Aisheng Dong <aisheng.dong@nxp.com>,
	"robh+dt@kernel.org" <robh+dt@kernel.org>,
	"krzysztof.kozlowski+dt@linaro.org"
	<krzysztof.kozlowski+dt@linaro.org>,
	"shawnguo@kernel.org" <shawnguo@kernel.org>,
	"s.hauer@pengutronix.de" <s.hauer@pengutronix.de>
Cc: "kernel@pengutronix.de" <kernel@pengutronix.de>,
	"festevam@gmail.com" <festevam@gmail.com>,
	dl-linux-imx <linux-imx@nxp.com>,
	"linux-i2c@vger.kernel.org" <linux-i2c@vger.kernel.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Clark Wang <xiaoning.wang@nxp.com>
Subject: RE: [PATCH 0/6] i2c-imx-lpi2c: add IPG clock
Date: Tue, 16 Aug 2022 06:31:22 +0000	[thread overview]
Message-ID: <DU0PR04MB94178FD1DEE5CCC8AF162E48886B9@DU0PR04MB9417.eurprd04.prod.outlook.com> (raw)
In-Reply-To: <039566a7-5c65-b2d8-7b45-c616863cb292@linaro.org>

> 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@nxp.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,

I see. But the current binding and dts using one clk is really wrong. Anyway,
I could make it backwards compatible.

Thanks,
Peng.
> 
> > 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
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