linux-kernel - Re: [PATCH 06/23] gpio: sysfs: clean up chip class-device handling

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Date:	Mon, 27 Apr 2015 12:54:41 +0900
From:	Alexandre Courbot <gnurou@...il.com>
To:	Johan Hovold <johan@...nel.org>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 06/23] gpio: sysfs: clean up chip class-device handling

On Wed, Apr 22, 2015 at 12:42 AM, Johan Hovold <johan@...nel.org> wrote:
> Clean gpio-chip class device registration and deregistration.
>
> The class device is registered when a gpio-chip is added (or from
> gpiolib_sysfs_init post-core init call), and deregistered when the chip
> is removed.
>
> Store the class device in struct gpio_chip directly rather than do a
> class-device lookup on deregistration. This also removes the need for
> the exported flag.
>
> Signed-off-by: Johan Hovold <johan@...nel.org>
> ---
>  drivers/gpio/gpiolib-sysfs.c | 39 +++++++++++++--------------------------
>  include/linux/gpio/driver.h  |  4 ++--
>  2 files changed, 15 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
> index c433f075f349..2f8bdce792f6 100644
> --- a/drivers/gpio/gpiolib-sysfs.c
> +++ b/drivers/gpio/gpiolib-sysfs.c
> @@ -567,7 +567,7 @@ int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
>         mutex_lock(&sysfs_lock);
>
>         /* check if chip is being removed */
> -       if (!chip || !chip->exported) {
> +       if (!chip || !chip->cdev) {
>                 status = -ENODEV;
>                 goto fail_unlock;
>         }
> @@ -752,7 +752,6 @@ EXPORT_SYMBOL_GPL(gpiod_unexport);
>
>  int gpiochip_export(struct gpio_chip *chip)
>  {
> -       int             status;
>         struct device   *dev;
>
>         /* Many systems register gpio chips for SOC support very early,
> @@ -768,41 +767,29 @@ int gpiochip_export(struct gpio_chip *chip)
>                                         chip, gpiochip_groups,
>                                         "gpiochip%d", chip->base);
>         if (IS_ERR(dev))
> -               status = PTR_ERR(dev);
> -       else
> -               status = 0;
> +               return PTR_ERR(dev);
>
>         mutex_lock(&sysfs_lock);
> -       chip->exported = (status == 0);
> +       chip->cdev = dev;
>         mutex_unlock(&sysfs_lock);
>
> -       if (status)
> -               chip_dbg(chip, "%s: status %d\n", __func__, status);
> -
> -       return status;
> +       return 0;
>  }
>
>  void gpiochip_unexport(struct gpio_chip *chip)
>  {
> -       int                     status;
> -       struct device           *dev;
>         struct gpio_desc *desc;
>         unsigned int i;
>
> -       dev = class_find_device(&gpio_class, NULL, chip, match_export);
> -       if (dev) {
> -               put_device(dev);
> -               device_unregister(dev);
> -               /* prevent further gpiod exports */
> -               mutex_lock(&sysfs_lock);
> -               chip->exported = false;
> -               mutex_unlock(&sysfs_lock);
> -               status = 0;
> -       } else
> -               status = -ENODEV;
> +       if (!chip->cdev)
> +               return;
>
> -       if (status)
> -               chip_dbg(chip, "%s: status %d\n", __func__, status);
> +       device_unregister(chip->cdev);
> +
> +       /* prevent further gpiod exports */
> +       mutex_lock(&sysfs_lock);
> +       chip->cdev = NULL;
> +       mutex_unlock(&sysfs_lock);
>
>         /* unregister gpiod class devices owned by sysfs */
>         for (i = 0; i < chip->ngpio; i++) {
> @@ -830,7 +817,7 @@ static int __init gpiolib_sysfs_init(void)
>          */
>         spin_lock_irqsave(&gpio_lock, flags);
>         list_for_each_entry(chip, &gpio_chips, list) {
> -               if (chip->exported)
> +               if (chip->cdev)
>                         continue;
>
>                 /*
> diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
> index f1b36593ec9f..8c26855fc6ec 100644
> --- a/include/linux/gpio/driver.h
> +++ b/include/linux/gpio/driver.h
> @@ -20,6 +20,7 @@ struct seq_file;
>   * struct gpio_chip - abstract a GPIO controller
>   * @label: for diagnostics
>   * @dev: optional device providing the GPIOs
> + * @cdev: class device (may be NULL)

Maybe a comment explaining that this field is non-NULL when a chip is
exported would be useful to understand how it is used in the code?
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