gpiolib: cdev: support edge detection for uAPI v2

Add support for edge detection to lines requested using
GPIO_V2_GET_LINE_IOCTL.

The edge_detector implementation is based on the v1 lineevent
implementation.  Unlike the v1 implementation, an overflow of the event
buffer results in discarding older events, rather than the most
recent, so the final event in a burst will correspond to the current
state of the line.
Signed-off-by: Kent Gibson <warthog618@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

drivers/gpio/gpiolib.c

@@ -2092,6 +2092,8 @@ static bool gpiod_free_commit(struct gpio_desc *desc)
 		clear_bit(FLAG_PULL_UP, &desc->flags);
 		clear_bit(FLAG_PULL_DOWN, &desc->flags);
 		clear_bit(FLAG_BIAS_DISABLE, &desc->flags);
+		clear_bit(FLAG_EDGE_RISING, &desc->flags);
+		clear_bit(FLAG_EDGE_FALLING, &desc->flags);
 		clear_bit(FLAG_IS_HOGGED, &desc->flags);
 #ifdef CONFIG_OF_DYNAMIC
 		desc->hog = NULL;

drivers/gpio/gpiolib.h

@@ -114,6 +114,8 @@ struct gpio_desc {
 #define FLAG_PULL_UP    13	/* GPIO has pull up enabled */
 #define FLAG_PULL_DOWN  14	/* GPIO has pull down enabled */
 #define FLAG_BIAS_DISABLE    15	/* GPIO has pull disabled */
+#define FLAG_EDGE_RISING     16	/* GPIO CDEV detects rising edge events */
+#define FLAG_EDGE_FALLING    17	/* GPIO CDEV detects falling edge events */
 
 	/* Connection label */
 	const char		*label;