gpio: Timestamp events in hardirq handler

 * @events: KFIFO for the GPIO events

 * @read_lock: mutex lock to protect reads from colliding with adding

 * new events to the FIFO

 * @timestamp: cache for the timestamp storing it between hardirq

 * and IRQ thread, used to bring the timestamp close to the actual

 * event

 */

struct lineevent_state {

	struct gpio_device *gdev;

	wait_queue_head_t wait;

	DECLARE_KFIFO(events, struct gpioevent_data, 16);

	struct mutex read_lock;

	u64 timestamp;

};

#define GPIOEVENT_REQUEST_VALID_FLAGS \

	/* Do not leak kernel stack to userspace */

	memset(&ge, 0, sizeof(ge));

	ge.timestamp = ktime_get_real_ns();

	ge.timestamp = le->timestamp;

	level = gpiod_get_value_cansleep(le->desc);

	if (le->eflags & GPIOEVENT_REQUEST_RISING_EDGE

	return IRQ_HANDLED;

}

static irqreturn_t lineevent_irq_handler(int irq, void *p)

{

	struct lineevent_state *le = p;

	/*

	 * Just store the timestamp in hardirq context so we get it as

	 * close in time as possible to the actual event.

	 */

	le->timestamp = ktime_get_real_ns();

	return IRQ_WAKE_THREAD;

}

static int lineevent_create(struct gpio_device *gdev, void __user *ip)

{

	struct gpioevent_request eventreq;

	/* Request a thread to read the events */

	ret = request_threaded_irq(le->irq,

			NULL,

			lineevent_irq_handler,

			lineevent_irq_thread,

			irqflags,

			le->label,