linux-kernel - Re: [PATCH] pwm: Add missing dummy for devm_pwmchip

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Date:   Wed, 26 Oct 2022 09:05:42 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Biju Das <biju.das.jz@...renesas.com>,
        linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pwm: Add missing dummy for devm_pwmchip_add()

Hi Uwe,

On Wed, Oct 26, 2022 at 2:17 AM Uwe Kleine-König
<u.kleine-koenig@...gutronix.de> wrote:
> On Tue, Oct 25, 2022 at 04:03:42PM +0200, Geert Uytterhoeven wrote:
> > The PWM subsystem supports compile-testing if CONFIG_PWM is disabled.
> > However, no dummy is provided for devm_pwmchip_add(), which may lead to
> > build failures.
> >
> > Fixes: bcda91bf86c1ff76 ("pwm: Add a device-managed function to add PWM chips")
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
>
> Is this a problem that today yields a failure to compile? As of v6.1-rc1
> and also in next all callers are below drivers/pwm/ which isn't included
> in the build without PWM=y.

So none of these support compile-testing with CONFIG_PWM=n...

> Am I missing something or is this just preparing that one of the drivers
> that doesn't live in drivers/pwm might call devm_pwmchip_add in the
> future?

I saw it with the RZ/G2L MTU3 PWM driver[1], which is not yet applied.
After noticing its sibling counter driver lacked a dependency on
CONFIG_COUNTER, I tried disabling CONFIG_PWM...

> In that case I wouldn't add that Fixes: line (and also oppose to
> backporting that commit to stable).

I tend to disagree: more drivers may be converted to devm_pwmchip_add()
in the future, possibly as part of a fix, causing troubles for the
stable team when backporting such fixes.

Thanks!

[1] https://lore.kernel.org/all/CAMuHMdWE+H=aXkt61hZK6mbQairwdk1F522mZRemC0T5LxQtMg@mail.gmail.com

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds