linux-kernel - Re: [PATCH 02/21] gpiolib: provide gpio_device

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Date:   Mon, 11 Sep 2023 15:14:42 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Aaro Koskinen <aaro.koskinen@....fi>,
        Janusz Krzysztofik <jmkrzyszt@...il.com>,
        Tony Lindgren <tony@...mide.com>,
        Russell King <linux@...linux.org.uk>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Dipen Patel <dipenp@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <markgross@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-omap@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-acpi@...r.kernel.org, timestamp@...ts.linux.dev,
        linux-tegra@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH 02/21] gpiolib: provide gpio_device_find()

On Wed, Sep 6, 2023 at 4:10 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Tue, Sep 05, 2023 at 08:52:50PM +0200, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >
> > gpiochip_find() is wrong and its kernel doc is misleading as the
> > function doesn't return a reference to the gpio_chip but just a raw
> > pointer. The chip itself is not guaranteed to stay alive, in fact it can
> > be deleted at any point. Also: other than GPIO drivers themselves,
> > nobody else has any business accessing gpio_chip structs.
> >
> > Provide a new gpio_device_find() function that returns a real reference
> > to the opaque gpio_device structure that is guaranteed to stay alive for
> > as long as there are active users of it.
>
> ...
>
> > +/**
> > + * gpio_device_find() - find a specific GPIO device
> > + * @data: data to pass to match function
> > + * @match: Callback function to check gpio_chip
>
> > + * Returns:
> > + * New reference to struct gpio_device.
>
> I believe this is wrong location of the Return section.
> AFAIU how kernel doc uses section markers, this entire description becomes
> a Return(s) section. Have you tried to render man/html/pdf and see this?
>

Yes, it works just fine. Try for yourself: scripts/kernel-doc -rst
drivers/gpio/gpiolib.c

Bart

> > + * Similar to bus_find_device(). It returns a reference to a gpio_device as
> > + * determined by a user supplied @match callback. The callback should return
> > + * 0 if the device doesn't match and non-zero if it does. If the callback
> > + * returns non-zero, this function will return to the caller and not iterate
> > + * over any more gpio_devices.
> > + *
> > + * The callback takes the GPIO chip structure as argument. During the execution
> > + * of the callback function the chip is protected from being freed. TODO: This
> > + * actually has yet to be implemented.
> > + *
> > + * If the function returns non-NULL, the returned reference must be freed by
> > + * the caller using gpio_device_put().
> > + */
> > +struct gpio_device *gpio_device_find(void *data,
>
> > +                                  int (*match)(struct gpio_chip *gc,
> > +                                               void *data))
>
> One line?
> Or maybe a type for it? (gpio_match_fn, for example)
>
> > +{
> > +     struct gpio_device *gdev;
> > +
> > +     guard(spinlock_irqsave)(&gpio_lock);
> > +
> > +     list_for_each_entry(gdev, &gpio_devices, list) {
> > +             if (gdev->chip && match(gdev->chip, data))
> > +                     return gpio_device_get(gdev);
> > +     }
> > +
> > +     return NULL;
> > +}
>
> ...
>
> > +struct gpio_device *gpio_device_find(void *data,
> > +                                  int (*match)(struct gpio_chip *gc,
> > +                                               void *data));
>
> Ditto.
>
>
> --
> With Best Regards,
> Andy Shevchenko
>
>