gpio: userspace ABI for reading GPIO line events

This adds an ABI for listening to events on GPIO lines.
The mechanism returns an anonymous file handle to a request
to listen to a specific offset on a specific gpiochip.
To fetch the stream of events from the file handle, userspace
simply reads an event.

- Events can be requested with the same flags as ordinary
  handles, i.e. open drain or open source. An ioctl() call
  GPIO_GET_LINEEVENT_IOCTL is issued indicating the desired
  line.

- Events can be requested for falling edge events, rising
  edge events, or both.

- All events are timestamped using the kernel real time
  nanosecond timestamp (the same as is used by IIO).

- The supplied consumer label will appear in "lsgpio"
  listings of the lines, and in /proc/interrupts as the
  mechanism will request an interrupt from the gpio chip.

- Events are not supported on gpiochips that do not serve
  interrupts (no legal .to_irq() call). The event interrupt
  is threaded to avoid any realtime problems.

- It is possible to also directly read the current value
  of the registered GPIO line by issuing the same
  GPIOHANDLE_GET_LINE_VALUES_IOCTL as used by the
  line handles. Setting the value is not supported: we
  do not listen to events on output lines.

This ABI is strongly influenced by Industrial I/O and surpasses
the old sysfs ABI by providing proper precision timestamps,
making it possible to set flags like open drain, and put
consumer names on the GPIO lines.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

include/uapi/linux/gpio.h

@@ -55,7 +55,7 @@ struct gpioline_info {
 /* Maximum number of requested handles */
 #define GPIOHANDLES_MAX 64
 
-/* Request flags */
+/* Linerequest flags */
 #define GPIOHANDLE_REQUEST_INPUT	(1UL << 0)
 #define GPIOHANDLE_REQUEST_OUTPUT	(1UL << 1)
 #define GPIOHANDLE_REQUEST_ACTIVE_LOW	(1UL << 2)
@@ -93,10 +93,6 @@ struct gpiohandle_request {
 	int fd;
 };
 
-#define GPIO_GET_CHIPINFO_IOCTL _IOR(0xB4, 0x01, struct gpiochip_info)
-#define GPIO_GET_LINEINFO_IOCTL _IOWR(0xB4, 0x02, struct gpioline_info)
-#define GPIO_GET_LINEHANDLE_IOCTL _IOWR(0xB4, 0x03, struct gpiohandle_request)
-
 /**
  * struct gpiohandle_data - Information of values on a GPIO handle
  * @values: when getting the state of lines this contains the current
@@ -110,4 +106,52 @@ struct gpiohandle_data {
 #define GPIOHANDLE_GET_LINE_VALUES_IOCTL _IOWR(0xB4, 0x08, struct gpiohandle_data)
 #define GPIOHANDLE_SET_LINE_VALUES_IOCTL _IOWR(0xB4, 0x09, struct gpiohandle_data)
 
+/* Eventrequest flags */
+#define GPIOEVENT_REQUEST_RISING_EDGE	(1UL << 0)
+#define GPIOEVENT_REQUEST_FALLING_EDGE	(1UL << 1)
+#define GPIOEVENT_REQUEST_BOTH_EDGES	((1UL << 0) | (1UL << 1))
+
+/**
+ * struct gpioevent_request - Information about a GPIO event request
+ * @lineoffset: the desired line to subscribe to events from, specified by
+ * offset index for the associated GPIO device
+ * @handleflags: desired handle flags for the desired GPIO line, such as
+ * GPIOHANDLE_REQUEST_ACTIVE_LOW or GPIOHANDLE_REQUEST_OPEN_DRAIN
+ * @eventflags: desired flags for the desired GPIO event line, such as
+ * GPIOEVENT_REQUEST_RISING_EDGE or GPIOEVENT_REQUEST_FALLING_EDGE
+ * @consumer_label: a desired consumer label for the selected GPIO line(s)
+ * such as "my-listener"
+ * @fd: if successful this field will contain a valid anonymous file handle
+ * after a GPIO_GET_LINEEVENT_IOCTL operation, zero or negative value
+ * means error
+ */
+struct gpioevent_request {
+	__u32 lineoffset;
+	__u32 handleflags;
+	__u32 eventflags;
+	char consumer_label[32];
+	int fd;
+};
+
+/**
+ * GPIO event types
+ */
+#define GPIOEVENT_EVENT_RISING_EDGE 0x01
+#define GPIOEVENT_EVENT_FALLING_EDGE 0x02
+
+/**
+ * struct gpioevent_data - The actual event being pushed to userspace
+ * @timestamp: best estimate of time of event occurrence, in nanoseconds
+ * @id: event identifier
+ */
+struct gpioevent_data {
+	__u64 timestamp;
+	__u32 id;
+};
+
+#define GPIO_GET_CHIPINFO_IOCTL _IOR(0xB4, 0x01, struct gpiochip_info)
+#define GPIO_GET_LINEINFO_IOCTL _IOWR(0xB4, 0x02, struct gpioline_info)
+#define GPIO_GET_LINEHANDLE_IOCTL _IOWR(0xB4, 0x03, struct gpiohandle_request)
+#define GPIO_GET_LINEEVENT_IOCTL _IOWR(0xB4, 0x04, struct gpioevent_request)
+
 #endif /* _UAPI_GPIO_H_ */