Re: [PATCH v2 21/23] gpio: protect the pointer to gpio_chip in gpio_device with SRCU

[Bartosz Golaszewski]

On Tue, Feb 6, 2024 at 2:13 PM Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx> 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.
>

I don't have a strong conviction here. May make it an error as well.
It's still inconsistent though - calling gpiod_direction_output(NULL);
will return 0 and then you get an error when you do
gpiod_get_direction(NULL). I don't have a good solution though.

Bart