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

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Message-ID: <4b15a9d3-23a4-43fe-a275-c9af11c6c8e1@wanadoo.fr>
Date: Thu, 12 Sep 2024 19:37:22 +0200
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Ard Biesheuvel <ardb@...nel.org>
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

Le 12/09/2024 à 19:12, Ard Biesheuvel a écrit :
> 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.

Got it, this is not related to the removed _OR_NULL, but to the change 
of logic I've introduce.

	if (!IS_ERR)
		do_something_and_continue;
	if_NOENT_was_returned_we_still_get_there();

which became:
	if (IS_ERR)
		return;
	we_can_get_there_with_NOENT_anymore();

My bad!

CJ

> 
> 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.
>