Re: [PATCH 1/2] gpiolib: add gpio_export_with_name

[Grant Likely <grant.likely@secretlab.ca>]

On Wed, 21 Nov 2012 11:14:08 +0100, Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com> wrote:
> allow to specify a name to an exported gpio
> 
> Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>

The gpio sysfs ABI is already horrible, racy, and unsafe. Really, we
need a proper chrdev interface for controlling gpios. Sysfs is fine for
poking around and experimenting, but we cannot provide any fine grained
access control, locking or faster IO with the one-file-per-gpio sysfs
model. So, no, I don't think this is a good idea to extend gpiolib in
this way.

However, I would be okay with making gpiochips first-class kobjects or
struct devices that appear as a child of the gpio controller device so
that userspace could interrogate the device tree node associated with
the device.

g.

> ---
>  arch/mips/include/asm/mach-au1x00/gpio-au1000.h |    3 ++-
>  arch/mips/include/asm/mach-au1x00/gpio-au1300.h |    3 ++-
>  drivers/gpio/gpiolib.c                          |   12 +++++++-----
>  include/asm-generic/gpio.h                      |    6 ++++--
>  include/linux/gpio.h                            |   23 ++++++++++++++++++++++-
>  5 files changed, 37 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/mips/include/asm/mach-au1x00/gpio-au1000.h b/arch/mips/include/asm/mach-au1x00/gpio-au1000.h
> index 73853b5a..af4accb 100644
> --- a/arch/mips/include/asm/mach-au1x00/gpio-au1000.h
> +++ b/arch/mips/include/asm/mach-au1x00/gpio-au1000.h
> @@ -633,7 +633,8 @@ static inline int gpio_set_debounce(unsigned gpio, unsigned debounce)
>  	return -ENOSYS;
>  }
>  
> -static inline int gpio_export(unsigned gpio, bool direction_may_change)
> +static inline int gpio_export_with_name(unsigned gpio,
> +	bool direction_may_change, const char *name)
>  {
>  	return -ENOSYS;
>  }
> diff --git a/arch/mips/include/asm/mach-au1x00/gpio-au1300.h b/arch/mips/include/asm/mach-au1x00/gpio-au1300.h
> index fb9975c..fcd152e 100644
> --- a/arch/mips/include/asm/mach-au1x00/gpio-au1300.h
> +++ b/arch/mips/include/asm/mach-au1x00/gpio-au1300.h
> @@ -234,7 +234,8 @@ static inline void gpio_unexport(unsigned gpio)
>  {
>  }
>  
> -static inline int gpio_export(unsigned gpio, bool direction_may_change)
> +static inline int gpio_export_with_name(unsigned gpio,
> +	bool direction_may_change, const char *name)
>  {
>  	return -ENOSYS;
>  }
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index b667f76..2141165 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -714,9 +714,10 @@ static struct class gpio_class = {
>  
>  
>  /**
> - * gpio_export - export a GPIO through sysfs
> + * gpio_export_with_name - export a GPIO through sysfs
>   * @gpio: gpio to make available, already requested
>   * @direction_may_change: true if userspace may change gpio direction
> + * @name: gpio name
>   * Context: arch_initcall or later
>   *
>   * When drivers want to make a GPIO accessible to userspace after they
> @@ -728,7 +729,7 @@ static struct class gpio_class = {
>   *
>   * Returns zero on success, else an error.
>   */
> -int gpio_export(unsigned gpio, bool direction_may_change)
> +int gpio_export_with_name(unsigned gpio, bool direction_may_change, const char *name)
>  {
>  	unsigned long		flags;
>  	struct gpio_desc	*desc;
> @@ -766,7 +767,9 @@ int gpio_export(unsigned gpio, bool direction_may_change)
>  		direction_may_change = false;
>  	spin_unlock_irqrestore(&gpio_lock, flags);
>  
> -	if (desc->chip->names && desc->chip->names[gpio - desc->chip->base])
> +	if (name)
> +		ioname = name;
> +	else if (desc->chip->names && desc->chip->names[gpio - desc->chip->base])
>  		ioname = desc->chip->names[gpio - desc->chip->base];
>  
>  	dev = device_create(&gpio_class, desc->chip->dev, MKDEV(0, 0),
> @@ -804,7 +807,7 @@ fail_unlock:
>  	pr_debug("%s: gpio%d status %d\n", __func__, gpio, status);
>  	return status;
>  }
> -EXPORT_SYMBOL_GPL(gpio_export);
> +EXPORT_SYMBOL_GPL(gpio_export_with_name);
>  
>  static int match_export(struct device *dev, void *data)
>  {
> @@ -856,7 +859,6 @@ done:
>  }
>  EXPORT_SYMBOL_GPL(gpio_export_link);
>  
> -
>  /**
>   * gpio_sysfs_set_active_low - set the polarity of gpio sysfs value
>   * @gpio: gpio to change
> diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
> index b6516f3..d04fc55 100644
> --- a/include/asm-generic/gpio.h
> +++ b/include/asm-generic/gpio.h
> @@ -204,7 +204,8 @@ void devm_gpio_free(struct device *dev, unsigned int gpio);
>   * A sysfs interface can be exported by individual drivers if they want,
>   * but more typically is configured entirely from userspace.
>   */
> -extern int gpio_export(unsigned gpio, bool direction_may_change);
> +extern int gpio_export_with_name(unsigned gpio, bool direction_may_change,
> +			const char *name);
>  extern int gpio_export_link(struct device *dev, const char *name,
>  			unsigned gpio);
>  extern int gpio_sysfs_set_active_low(unsigned gpio, int value);
> @@ -249,7 +250,8 @@ struct device;
>  
>  /* sysfs support is only available with gpiolib, where it's optional */
>  
> -static inline int gpio_export(unsigned gpio, bool direction_may_change)
> +static inline int gpio_export_with_name(unsigned gpio,
> +	bool direction_may_change, const char *name)
>  {
>  	return -ENOSYS;
>  }
> diff --git a/include/linux/gpio.h b/include/linux/gpio.h
> index 7ba2762..6e01b8c 100644
> --- a/include/linux/gpio.h
> +++ b/include/linux/gpio.h
> @@ -189,7 +189,8 @@ static inline void gpio_set_value_cansleep(unsigned gpio, int value)
>  	WARN_ON(1);
>  }
>  
> -static inline int gpio_export(unsigned gpio, bool direction_may_change)
> +static inline int gpio_export_with_name(unsigned gpio,
> +	bool direction_may_change, const char *name)
>  {
>  	/* GPIO can never have been requested or set as {in,out}put */
>  	WARN_ON(1);
> @@ -247,4 +248,24 @@ gpiochip_remove_pin_ranges(struct gpio_chip *chip)
>  
>  #endif /* ! CONFIG_GENERIC_GPIO */
>  
> +/**
> + * gpio_export - export a GPIO through sysfs
> + * @gpio: gpio to make available, already requested
> + * @direction_may_change: true if userspace may change gpio direction
> + * Context: arch_initcall or later
> + *
> + * When drivers want to make a GPIO accessible to userspace after they
> + * have requested it -- perhaps while debugging, or as part of their
> + * public interface -- they may use this routine.  If the GPIO can
> + * change direction (some can't) and the caller allows it, userspace
> + * will see "direction" sysfs attribute which may be used to change
> + * the gpio's direction.  A "value" attribute will always be provided.
> + *
> + * Returns zero on success, else an error.
> + */
> +static inline int gpio_export(unsigned gpio,bool direction_may_change)
> +{
> +	return gpio_export_with_name(gpio, direction_may_change, NULL);
> +}
> +
>  #endif /* __LINUX_GPIO_H */
> -- 
> 1.7.10.4
> 
> 
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-- 
Grant Likely, B.Sc, P.Eng.
Secret Lab Technologies, Ltd.