linux-kernel - Re: [PATCH] driver: pca953x: avoid error message when resuming

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Date:   Tue, 28 Jun 2022 14:35:30 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Pierluigi Passaro <pierluigi.p@...iscite.com>,
        Wolfram Sang <wsa@...nel.org>,
        Alifer Willians de Moraes <alifer.m@...iscite.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Eran Matityahu <eran.m@...iscite.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Francesco Ferraro <francesco.f@...iscite.com>
Subject: Re: [PATCH] driver: pca953x: avoid error message when resuming

On Mon, Jun 20, 2022 at 6:03 PM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
> On Mon, Jun 20, 2022 at 4:18 PM Pierluigi Passaro
> <pierluigi.p@...iscite.com> wrote:

> > > > Avoids the error messages "pca953x 1-0020: failed reading register"
> > > > when resuming from suspend using gpio-key attached to pca9534.
> > > Thanks for your report and fix. My comments below.
> > > First of all, how many of them do you get and why is it a problem?
> >
> > The number of occurrences depends on the time required to I2C bus to fully wake-up.
> > It's not a real problem, but the message may lead to think about a real I2C problem.
>
> Wolfram, do we have any mechanisms that guarantees that I2C traffic is
> not going on a semi-woken up host controller?
>
> Writing this, I'm in doubt this patch is a fix we want. Wouldn't it
> just hide the real issue with some resume ordering?

That sounds like a bug in the pm routines in the I2C driver. Why is it
returning from [runtime_]resume() if it is not properly resumed?

Yours,
Linus Walleij