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

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Message-ID: <ZPiISpLoVx35PuYc@smile.fi.intel.com>
Date:   Wed, 6 Sep 2023 17:10:18 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
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 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?

> + * 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