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From:   Bartosz Golaszewski <bgolaszewski@baylibre.com>
Date:   Mon, 29 Jun 2020 16:25:22 +0200
Message-ID: <CAMpxmJVQmo2S6AQgcPACHH8ziSQNUvAhkUJ3eW_YsLkbyGzm=Q@mail.gmail.com>
Subject: Re: [PATCH 14/22] gpiolib: make cdev a build option
To:     Kent Gibson <warthog618@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        linux-gpio <linux-gpio@vger.kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>
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On Tue, Jun 23, 2020 at 6:02 AM Kent Gibson <warthog618@gmail.com> wrote:
>
> Make the gpiolib-cdev module a build option.  This allows the CDEV
> interface to be removed from the kernel to reduce kernel size in
> applications where is it not required, and provides the parent for
> other other CDEV interface specific build options to follow.
>
> Suggested-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> Signed-off-by: Kent Gibson <warthog618@gmail.com>
>
> ---
>  drivers/gpio/Kconfig        | 16 ++++++++++++++--
>  drivers/gpio/Makefile       |  2 +-
>  drivers/gpio/gpiolib-cdev.h | 15 +++++++++++++++
>  3 files changed, 30 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
> index c6b5c65c8405..affc1524bc2c 100644
> --- a/drivers/gpio/Kconfig
> +++ b/drivers/gpio/Kconfig
> @@ -66,8 +66,20 @@ config GPIO_SYSFS
>
>           This ABI is deprecated. If you want to use GPIO from userspace,
>           use the character device /dev/gpiochipN with the appropriate
> -         ioctl() operations instead. The character device is always
> -         available.
> +         ioctl() operations instead.
> +
> +config GPIO_CDEV
> +       bool "/dev/gpiochipN (character device interface)"
> +       default y
> +       help
> +         Say Y here to add the character device /dev/gpiochipN interface
> +         for GPIOs. The character device allows userspace to control GPIOs
> +         using ioctl() operations.
> +
> +         Only say N is you are sure that the GPIO character device is not
> +         required.
> +
> +         If unsure, say Y.
>
>  config GPIO_GENERIC
>         depends on HAS_IOMEM # Only for IOMEM drivers
> diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
> index ef666cfef9d0..45eb09808d12 100644
> --- a/drivers/gpio/Makefile
> +++ b/drivers/gpio/Makefile
> @@ -7,8 +7,8 @@ obj-$(CONFIG_GPIOLIB)           += gpiolib.o
>  obj-$(CONFIG_GPIOLIB)          += gpiolib-devres.o
>  obj-$(CONFIG_GPIOLIB)          += gpiolib-legacy.o
>  obj-$(CONFIG_GPIOLIB)          += gpiolib-devprop.o
> -obj-$(CONFIG_GPIOLIB)          += gpiolib-cdev.o
>  obj-$(CONFIG_OF_GPIO)          += gpiolib-of.o
> +obj-$(CONFIG_GPIO_CDEV)                += gpiolib-cdev.o
>  obj-$(CONFIG_GPIO_SYSFS)       += gpiolib-sysfs.o
>  obj-$(CONFIG_GPIO_ACPI)                += gpiolib-acpi.o
>
> diff --git a/drivers/gpio/gpiolib-cdev.h b/drivers/gpio/gpiolib-cdev.h
> index 973578e7ad10..19a4e3d57120 100644
> --- a/drivers/gpio/gpiolib-cdev.h
> +++ b/drivers/gpio/gpiolib-cdev.h
> @@ -5,7 +5,22 @@
>
>  #include <linux/device.h>
>
> +#ifdef CONFIG_GPIO_CDEV
> +
>  int gpiolib_cdev_register(struct gpio_device *gdev, dev_t devt);
>  void gpiolib_cdev_unregister(struct gpio_device *gdev);
>
> +#else
> +
> +static inline int gpiolib_cdev_register(struct gpio_device *gdev, dev_t devt)
> +{
> +       return 0;
> +}
> +
> +static inline void gpiolib_cdev_unregister(struct gpio_device *gdev)
> +{
> +}
> +
> +#endif /* CONFIG_GPIO_CDEV */
> +
>  #endif /* GPIOLIB_CDEV_H */
> --
> 2.27.0
>

I know Linus doesn't like this, but I'm personally in favor of adding
this as long as it's enabled by default.

Reviewed-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>