gpio: add flags argument to gpiod_get*() functions

The huge majority of GPIOs have their direction and initial value set
right after being obtained by one of the gpiod_get() functions. The
integer GPIO API had gpio_request_one() that took a convenience flags
parameter allowing to specify an direction and value applied to the
returned GPIO. This feature greatly simplifies client code and ensures
errors are always handled properly.

A similar feature has been requested for the gpiod API. Since setting
the direction of a GPIO is so often the very next action done after
obtaining its descriptor, we prefer to extend the existing functions
instead of introducing new functions that would raise the
number of gpiod getters to 16 (!).

The drawback of this approach is that all gpiod clients need to be
updated. To limit the pain, temporary macros are introduced that allow
gpiod_get*() to be called with or without the extra flags argument. They
will be removed once all consumer code has been updated.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 20 insertions, 6 deletions

diff --git a/Documentation/gpio/consumer.txt b/Documentation/gpio/consumer.txt
index d8abfc31abbe..76546324e968 100644
--- a/Documentation/gpio/consumer.txt
+++ b/Documentation/gpio/consumer.txt
@@ -29,13 +29,24 @@ gpiod_get() functions. Like many other kernel subsystems, gpiod_get() takes the
 device that will use the GPIO and the function the requested GPIO is supposed to
 fulfill:
 
-        struct gpio_desc *gpiod_get(struct device *dev, const char *con_id)
+        struct gpio_desc *gpiod_get(struct device *dev, const char *con_id,
+                                    enum gpiod_flags flags)
 
 If a function is implemented by using several GPIOs together (e.g. a simple LED
 device that displays digits), an additional index argument can be specified:
 
         struct gpio_desc *gpiod_get_index(struct device *dev,
-                                          const char *con_id, unsigned int idx)
+                                          const char *con_id, unsigned int idx,
+                                          enum gpiod_flags flags)
+
+The flags parameter is used to optionally specify a direction and initial value
+for the GPIO. Values can be:
+
+* GPIOD_ASIS or 0 to not initialize the GPIO at all. The direction must be set
+  later with one of the dedicated functions.
+* GPIOD_IN to initialize the GPIO as input.
+* GPIOD_OUT_LOW to initialize the GPIO as output with a value of 0.
+* GPIOD_OUT_HIGH to initialize the GPIO as output with a value of 1.
 
 Both functions return either a valid GPIO descriptor, or an error code checkable
 with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
@@ -46,11 +57,13 @@ errors and an absence of GPIO for optional GPIO parameters.
 
 Device-managed variants of these functions are also defined:
 
-        struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id)
+        struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id,
+                                         enum gpiod_flags flags)
 
         struct gpio_desc *devm_gpiod_get_index(struct device *dev,
                                                const char *con_id,
-                                               unsigned int idx)
+                                               unsigned int idx,
+                                               enum gpiod_flags flags)
 
 A GPIO descriptor can be disposed of using the gpiod_put() function:
 
@@ -67,8 +80,9 @@ Using GPIOs
 
 Setting Direction
 -----------------
-The first thing a driver must do with a GPIO is setting its direction. This is
-done by invoking one of the gpiod_direction_*() functions:
+The first thing a driver must do with a GPIO is setting its direction. If no
+direction-setting flags have been given to gpiod_get*(), this is done by
+invoking one of the gpiod_direction_*() functions:
 
         int gpiod_direction_input(struct gpio_desc *desc)
         int gpiod_direction_output(struct gpio_desc *desc, int value)