linux-kernel - Re: [PATCH v2 21/23] gpio: protect the pointer to gpio_chip in gpio

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Message-ID: <ZcIwiU4UNbcoa8Km@smile.fi.intel.com>
Date: Tue, 6 Feb 2024 15:13:45 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Linus Walleij <linus.walleij@...aro.org>,
	Kent Gibson <warthog618@...il.com>, Alex Elder <elder@...aro.org>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Wolfram Sang <wsa@...-dreams.de>, linux-gpio@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v2 21/23] gpio: protect the pointer to gpio_chip in
 gpio_device with SRCU

On Tue, Feb 06, 2024 at 01:57:39PM +0100, Bartosz Golaszewski wrote:
> On Tue, Feb 6, 2024 at 1:24 PM Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
> >
> > On Mon, Feb 05, 2024 at 08:36:39PM +0100, Bartosz Golaszewski wrote:
> > > On Mon, Feb 5, 2024 at 1:31 PM Andy Shevchenko
> > > <andriy.shevchenko@...ux.intel.com> wrote:
> >
> > ...
> >
> > > >
> > > > >  int gpiod_get_direction(struct gpio_desc *desc)
> > > > >  {
> > > > > -     struct gpio_chip *gc;
> > > > >       unsigned long flags;
> > > > >       unsigned int offset;
> > > > >       int ret;
> > > > >
> > > > > -     gc = gpiod_to_chip(desc);
> > > > > +     if (!desc)
> > > > > +             /* Sane default is INPUT. */
> > > > > +             return 1;
> > > >
> > > > Hmm... I can't imagine how this value may anyhow be used / useful.
> > >
> > > What else would you return for an optional (NULL) GPIO?
> >
> > An error. If somebody asks for direction of the non-existing GPIO, there is no
> > (valid) answer for that.

> All other functions return 0 for desc == NULL to accommodate
> gpiod_get_optional(). I think we should stay consistent here.

The way you proposed is inconsistent, i.e. you may not return any direction
for the unknown / non-existing GPIO. You speculate it will be 1, I may consider
that in my (hypothetical for now) case it should be 0.

Just don't make all bananas to be oranges. It won't work.

-- 
With Best Regards,
Andy Shevchenko