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

[Sascha Hauer]

On Thu, Jun 01, 2017 at 01:33:55PM -0700, Andrey Smirnov wrote:
> On Thu, Jun 1, 2017 at 12:19 AM, Sascha Hauer <s.hauer at pengutronix.de> wrote:
> > 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 :(
> 
> So do we want to:
> 
> a) Keep things as is in v2(I am assuming that is not really an option)
> b) Improve the optics by introducing GPIOF_INIT_ACTIVE, but keeping
> the behavior of hog nodes consistent with Linux kernel

We must keep the behaviour consistent with the Kernel, everything else
is not an option. A GPIOF_INIT_ACTIVE flag sounds like a good idea. The
place where "output-[high|low]" is translated into this flag seems a
good place to put a big comment what is going on.

Sascha

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