linux-kernel - Re: [PATCH v3 2/7] gpiolib: Add support for gpiochipN-based table lookup

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Date:   Thu, 12 Dec 2019 14:33:24 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Jonathan Corbet <corbet@....net>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Harish Jenny K N <harish_kandiga@...tor.com>,
        Eugeniu Rosca <erosca@...adit-jv.com>,
        Alexander Graf <graf@...zon.com>,
        Peter Maydell <peter.maydell@...aro.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Phil Reid <preid@...ctromag.com.au>,
        Marc Zyngier <marc.zyngier@....com>,
        Christoffer Dall <christoffer.dall@....com>,
        Magnus Damm <magnus.damm@...il.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        QEMU Developers <qemu-devel@...gnu.org>
Subject: Re: [PATCH v3 2/7] gpiolib: Add support for gpiochipN-based table lookup

Hi Linus,

On Thu, Dec 12, 2019 at 2:20 PM Linus Walleij <linus.walleij@...aro.org> wrote:
> On Wed, Nov 27, 2019 at 9:43 AM Geert Uytterhoeven
> <geert+renesas@...der.be> wrote:
> > Currently GPIO controllers can only be referred to by label in GPIO
> > lookup tables.
> >
> > Add support for looking them up by "gpiochipN" name, with "N" either the
> > corresponding GPIO device's ID number, or the GPIO controller's first
> > GPIO number.
> >
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
>
> What the commit message is missing is a rationale, why is this needed?

Right. To be added: so they can be looked up in the GPIO lookup table
using either the chip's label, or the "gpiochipN" name.

> > If this is rejected, the GPIO Aggregator documentation must be updated.
> >
> > The second variant is currently used by the legacy sysfs interface only,
> > so perhaps the chip->base check should be dropped?
>
> Anything improving the sysfs is actively discouraged by me.
> If it is just about staying compatible it is another thing.

OK, so N must be the corresponding GPIO device's ID number.

> > +static int gpiochip_match_id(struct gpio_chip *chip, void *data)
> > +{
> > +       int id = (uintptr_t)data;
> > +
> > +       return id == chip->base || id == chip->gpiodev->id;
> > +}
> >  static struct gpio_chip *find_chip_by_name(const char *name)
> >  {
> > -       return gpiochip_find((void *)name, gpiochip_match_name);
> > +       struct gpio_chip *chip;
> > +       int id;
> > +
> > +       chip = gpiochip_find((void *)name, gpiochip_match_name);
> > +       if (chip)
> > +               return chip;
> > +
> > +       if (!str_has_prefix(name, GPIOCHIP_NAME))
> > +               return NULL;
> > +
> > +       if (kstrtoint(name + strlen(GPIOCHIP_NAME), 10, &id))
> > +               return NULL;
> > +
> > +       return gpiochip_find((void *)(uintptr_t)id, gpiochip_match_id);
>
> Isn't it easier to just  augment the existing match function to
> check like this:
>
> static int gpiochip_match_name(struct gpio_chip *chip, void *data)
> {
>         const char *name = data;
>
>         if (!strcmp(chip->label, name))
>                return 0;

return true;

>         return !strcmp(dev_name(&chip->gpiodev->dev), name);
> }

Oh, didn't think of using dev_name() on the gpiodev.
Yes, with the chip->base check removed, the code can be simplified.

Or just

        return !strcmp(chip->label, name) ||
               !strcmp(dev_name(&chip->gpiodev->dev), name);

> We should I guess also add some kerneldoc to say we first
> match on the label and second on dev_name().

OK.

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