linux-kernel - Re: [PATCH v5 09/12] gpio: aggregator: handle runtime registration of gpio_desc in gpiochip

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Message-ID: <CAHp75VcKsq5_+uwwVKeq8++H+Rw1giH-TKUErsFmdKPiu5kY+A@mail.gmail.com>
Date: Wed, 7 May 2025 16:24:14 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Thomas Richard <thomas.richard@...tlin.com>
Cc: Linus Walleij <linus.walleij@...aro.org>, 
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Bartosz Golaszewski <brgl@...ev.pl>, 
	Geert Uytterhoeven <geert+renesas@...der.be>, Kees Cook <kees@...nel.org>, 
	Andy Shevchenko <andy@...nel.org>, linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org, 
	thomas.petazzoni@...tlin.com, DanieleCleri@...on.eu, GaryWang@...on.com.tw, 
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH v5 09/12] gpio: aggregator: handle runtime registration of
 gpio_desc in gpiochip_fwd

On Wed, May 7, 2025 at 1:10 PM Thomas Richard
<thomas.richard@...tlin.com> wrote:
> On 5/7/25 08:34, Andy Shevchenko wrote:
> > On Tue, May 6, 2025 at 6:21 PM Thomas Richard
> > <thomas.richard@...tlin.com> wrote:

...

> >> +       /*
> >> +        * get_direction() is called during gpiochip registration, return input
> >> +        * direction if there is no descriptor for the line.
> >> +        */
> >> +       if (!test_bit(offset, fwd->valid_mask))
> >> +               return GPIO_LINE_DIRECTION_IN;
> >
> > Can you remind me why we choose a valid return for invalid line? From
> > a pure code perspective this should return an error.
>
> I reproduced gpiolib behavior. During gpiochip registration, we get the
> direction of all lines. In the case the line is not valid, it is marked
> as input if direction_input operation exists, otherwise it is marked as
> output. [1]
>
> But in fact we could return an error and the core will mark the line as
> input. Maybe ENODEV ?

I am fine with this error code, but do we have similar cases already
in the kernel? Do they use the same or different error code(s)?

> [1]
> https://elixir.bootlin.com/linux/v6.15-rc5/source/drivers/gpio/gpiolib.c#L1105-L1123

-- 
With Best Regards,
Andy Shevchenko