Re: [PATCH] gpio: mockup: allocate lines with main struct

[Rosen Penev]

On Tue, Mar 24, 2026 at 8:54 AM Bartosz Golaszewski <brgl@xxxxxxxxxx> wrote:
>
> On Tue, Mar 24, 2026 at 4:52 PM Rosen Penev <rosenp@xxxxxxxxx> wrote:
> >
> > On Tue, Mar 24, 2026 at 2:16 AM Bartosz Golaszewski <brgl@xxxxxxxxxx> wrote:
> > >
> > > On Mon, 23 Mar 2026 17:43:00 +0100, Rosen Penev <rosenp@xxxxxxxxx> said:
> > > > On Mon, Mar 23, 2026 at 3:00 AM Bartosz Golaszewski <brgl@xxxxxxxxxx> wrote:
> > > >>
> > > >> On Sat, Mar 21, 2026 at 12:00 AM Rosen Penev <rosenp@xxxxxxxxx> wrote:
> > > >> >
> > > >> > >
> > > >> > > static int gpio_mockup_probe(struct platform_device *pdev)
> > > >> > > {
> > > >> > >         ...
> > > >> > >         u16 ngpio;
> > > >> > >         ...
> > > >> > >         rv = device_property_read_u16(dev, "nr-gpios", &ngpio);
> > > >> > >         ...
> > > >> > >         gc->ngpio = ngpio;
> > > >> > >         ...
> > > >> > >         chip->lines = devm_kcalloc(dev, gc->ngpio,
> > > >> > >                                    sizeof(*chip->lines), GFP_KERNEL);
> > > >> > >
> > > >> > > But this begs the question: why add nr_lines when ngpio is already part
> > > >> > > of the struct:
> > > >> > Maintainers for some inexplicable reason want an extra variable for
> > > >> > __counted_by works.
> > > >>
> > > >> I believe what Kees means here is: you can use ngpio for __counted_by() like so:
> > > >>
> > > >>   __counted_by(gc.ngpio)
> > > > __counted_by doesn't support nested variables like that.
> > > >
> > > > drivers/gpio/gpio-mockup.c:59:61: error: ‘gc’ undeclared here (not in
> > > > a function)
> > > >    59 |         struct gpio_mockup_line_status lines[] __counted_by(gc.ngpio);
> > >
> > > The following spin on your patch builds fine for me:
> > >
> > > diff --git a/drivers/gpio/gpio-mockup.c b/drivers/gpio/gpio-mockup.c
> > > index a7d69f3835c1e..9427ab8c45f73 100644
> > > --- a/drivers/gpio/gpio-mockup.c
> > > +++ b/drivers/gpio/gpio-mockup.c
> > > @@ -52,10 +52,10 @@ struct gpio_mockup_line_status {
> > >
> > >  struct gpio_mockup_chip {
> > >         struct gpio_chip gc;
> > > -       struct gpio_mockup_line_status *lines;
> > >         struct irq_domain *irq_sim_domain;
> > >         struct dentry *dbg_dir;
> > >         struct mutex lock;
> > > +       struct gpio_mockup_line_status lines[] __counted_by(gc.ngpio);
> > You're using an older compiler. This does not work at all.
> >
> >  * Optional: only supported since gcc >= 15
> >  * Optional: only supported since clang >= 18
> > >  };
> > >
>
> Ok, what is this feature called in gcc parlance and where does this
> info come from?
include/linux/compiler_types.h

Lines 363-364 in linux-next.
>
> Bart