[PATCH v2 2/4] gpiolib: Add code to support "active low" GPIOs

[Sascha Hauer]

On Tue, May 30, 2017 at 07:52:26AM -0700, Andrey Smirnov wrote:
> So far this particular aspect of various DT-bindings has been handled
> on a per-driver basis. With this change, hopefully, we'll have a
> single place to handle necessary logic inversions and eventually
> would be able to migrate existing users as well as avoiding adding
> redundant code to new drivers.
> 
> Cc: cphealy at gmail.com
> Cc: Nikita Yushchenko <nikita.yoush at cogentembedded.com>
> Signed-off-by: Andrey Smirnov <andrew.smirnov at gmail.com>
> ---
>  drivers/gpio/gpiolib.c | 42 ++++++++++++++++++++++++++++++++++++++++--
>  include/gpio.h         | 20 ++++++++++++++++++++
>  2 files changed, 60 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 1f57c76..36d8874 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -13,6 +13,7 @@ static LIST_HEAD(chip_list);
>  struct gpio_info {
>  	struct gpio_chip *chip;
>  	bool requested;
> +	bool active_low;
>  	char *label;
>  };
>  
> @@ -45,6 +46,15 @@ static struct gpio_info *gpio_to_desc(unsigned gpio)
>  	return NULL;
>  }
>  
> +static int gpio_adjust_value(struct gpio_info *gi,
> +			     int value)
> +{
> +	if (value < 0)
> +		return value;
> +
> +	return !!value ^ gi->active_low;
> +}
> +
>  int gpio_request(unsigned gpio, const char *label)
>  {
>  	struct gpio_info *gi = gpio_to_desc(gpio);
> @@ -69,6 +79,7 @@ int gpio_request(unsigned gpio, const char *label)
>  	}
>  
>  	gi->requested = true;
> +	gi->active_low = false;
>  	gi->label = xstrdup(label);
>  
>  done:
> @@ -93,6 +104,7 @@ void gpio_free(unsigned gpio)
>  		gi->chip->ops->free(gi->chip, gpio - gi->chip->base);
>  
>  	gi->requested = false;
> +	gi->active_low = false;
>  	free(gi->label);
>  	gi->label = NULL;
>  }
> @@ -111,10 +123,15 @@ int gpio_request_one(unsigned gpio, unsigned long flags, const char *label)
>  	if (err)
>  		return err;
>  
> +	if (flags & GPIOF_ACTIVE_LOW) {
> +		struct gpio_info *gi = gpio_to_desc(gpio);
> +		gi->active_low = true;
> +	}
> +
>  	if (flags & GPIOF_DIR_IN)
>  		err = gpio_direction_input(gpio);
>  	else
> -		err = gpio_direction_output(gpio,
> +		err = gpio_direction_active(gpio,
>  				(flags & GPIOF_INIT_HIGH) ? 1 : 0);

And here things get messy.

For me 'high' and 'low' represent the physical values of a GPIO whereas
"active" and "inactive" represent the logical values of a GPIO. The flag
is named GPIOF_INIT_*HIGH*, not GPIOF_INIT_*ACTIVE*, which means a GPIO
with this flag should get the physical 'high' value, not the logical
'active' value.

They goofed the binding in the kernel, so I'm afraid there's nothing we
can do about this :(

Sascha


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