linux-kernel - Re: [PATCH] i2c/synquacer: Deal with optional PCLK correctly

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Message-ID: <CAMj1kXEYpD4LdZ9jQebyViWW98ogX7=tKzQNLNZxdBUORgpnQg@mail.gmail.com>
Date: Thu, 12 Sep 2024 19:12:56 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: "Marion & Christophe JAILLET" <christophe.jaillet@...adoo.fr>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, linux-i2c@...r.kernel.org, stable@...r.kernel.org, 
	Andi Shyti <andi.shyti@...nel.org>, Andy Shevchenko <andy.shevchenko@...il.com>, 
	Wolfram Sang <wsa@...nel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	Kernel Janitors <kernel-janitors@...r.kernel.org>
Subject: Re: [PATCH] i2c/synquacer: Deal with optional PCLK correctly

On Thu, 12 Sept 2024 at 19:11, Marion & Christophe JAILLET
<christophe.jaillet@...adoo.fr> wrote:
>
> (trying to merge t and cc fields from Ard's and Andy's messages)
>
>
> Le 12/09/2024 à 12:46, Ard Biesheuvel a écrit :
> > From: Ard Biesheuvel <ardb@...nel.org>
> >
> > ACPI boot does not provide clocks and regulators, but instead, provides
> > the PCLK rate directly, and enables the clock in firmware. So deal
> > gracefully with this.
> >
> > Fixes: 55750148e559 ("i2c: synquacer: Fix an error handling path in synquacer_i2c_probe()")
>
> Hi,
>
> If that matters, I'm not sure that the Fixes tag is correct.
>
> IIUC, either it is a new functionally that is added (now it works with
> ACPI...), or if considered as a fix, then I think that it is linked to
> commit 0d676a6c4390 ("i2c: add support for Socionext SynQuacer I2C
> controller").
>
> I don't think that 55750148e559 introduced a regression. The issue seems
> to be there since the beginning. Agreed?
>

No.

The original code used IS_ERR_OR_NULL() to explicitly permit the case
where no clock exists at all.

This has worked fine with ACPI boot for many years before this fix was applied.

> If yes, then it may be needed to backport it in older kernels too.
>

No, it used to work. The fix is what broke ACPI boot.

-- 
Ard.