linux-kernel - Re: [PATCH] gpio: aggregator: restore the set

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Message-ID: <CAMuHMdU_3Wfzq_qc9odGYtSAsMMOgww90qyH+GN4eQ7cxJMG+g@mail.gmail.com>
Date: Mon, 6 Oct 2025 09:42:52 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Thomas Richard <thomas.richard@...tlin.com>
Cc: Linus Walleij <linus.walleij@...aro.org>, Bartosz Golaszewski <brgl@...ev.pl>, 
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>, linux-gpio@...r.kernel.org, 
	linux-kernel@...r.kernel.org, kernel test robot <oliver.sang@...el.com>
Subject: Re: [PATCH] gpio: aggregator: restore the set_config operation

Hi Thomas,

On Fri, 3 Oct 2025 at 16:30, Thomas Richard <thomas.richard@...tlin.com> wrote:
> On 10/3/25 3:59 PM, Thomas Richard wrote:
> >> Is there any specific reason why you are doing this unconditionally,
> >> instead of only when any of its parents support .set_config(), like
> >> was done before?
> >>
> > My idea was: it will be handled by the core, so the if statement is not
> > needed. But if we conditionally add the operation we can save some time
> > in case there is no chip supporting set_config().
>
> I just remembered the true reason why I'm doing this unconditionally.
>
> The user of the forwarder can override GPIO operations like I do in the
> pinctrl-upboard driver [1].
> And now we can add/remove GPIO desc at runtime, if set_config() is set
> conditionally in gpiochip_fwd_desc_add() it will override the custom
> set_config() operation.
> So the only solution is to set the set_config() operation
> unconditionally in devm_gpiochip_fwd_alloc().

OK, that makes sense, so
Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>

I do find this overriding a bit fragile.
And in theory, such a driver could override chip->can_sleep to false,
which might be overwritten again by gpiochip_fwd_desc_add()...

> [1]
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pinctrl/pinctrl-upboard.c#n1044

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