[PATCH v10 09/20] gpiolib: cdev: support edge detection for uAPI v2

[Kent Gibson <warthog618@gmail.com>]

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>
---

The linereq_put_event() helper is only used once here, but is re-used in
subsequent patches, and so is pre-emptively split out.

edge_detector_stop() is extended in subsequent patches, and is structured
to suit those additions.

 drivers/gpio/gpiolib-cdev.c | 277 ++++++++++++++++++++++++++++++++++++
 drivers/gpio/gpiolib.c      |   2 +
 drivers/gpio/gpiolib.h      |   2 +
 3 files changed, 281 insertions(+)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index 786e667cdc85..868fcf89478c 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -404,9 +404,33 @@ static int linehandle_create(struct gpio_device *gdev, void __user *ip)
 /**
  * struct line - contains the state of a requested line
  * @desc: the GPIO descriptor for this line.
+ * @req: the corresponding line request
+ * @irq: the interrupt triggered in response to events on this GPIO
+ * @eflags: the edge flags, GPIO_V2_LINE_FLAG_EDGE_RISING and/or
+ * GPIO_V2_LINE_FLAG_EDGE_FALLING, indicating the edge detection applied
+ * @timestamp_ns: cache for the timestamp storing it between hardirq and
+ * IRQ thread, used to bring the timestamp close to the actual event
+ * @req_seqno: the seqno for the current edge event in the sequence of
+ * events for the corresponding line request. This is drawn from the @req.
+ * @line_seqno: the seqno for the current edge event in the sequence of
+ * events for this line.
  */
 struct line {
 	struct gpio_desc *desc;
+	/*
+	 * -- edge detector specific fields --
+	 */
+	struct linereq *req;
+	unsigned int irq;
+	u64 eflags;
+	/*
+	 * timestamp_ns and req_seqno are accessed only by
+	 * edge_irq_handler() and edge_irq_thread(), which are themselves
+	 * mutually exclusive, so no additional protection is necessary.
+	 */
+	u64 timestamp_ns;
+	u32 req_seqno;
+	u32 line_seqno;
 };
 
 /**
@@ -414,12 +438,22 @@ struct line {
  * @gdev: the GPIO device the line request pertains to
  * @label: consumer label used to tag GPIO descriptors
  * @num_lines: the number of lines in the lines array
+ * @wait: wait queue that handles blocking reads of events
+ * @event_buffer_size: the number of elements allocated in @events
+ * @events: KFIFO for the GPIO events
+ * @seqno: the sequence number for edge events generated on all lines in
+ * this line request.  Note that this is not used when @num_lines is 1, as
+ * the line_seqno is then the same and is cheaper to calculate.
  * @lines: the lines held by this line request, with @num_lines elements.
  */
 struct linereq {
 	struct gpio_device *gdev;
 	const char *label;
 	u32 num_lines;
+	wait_queue_head_t wait;
+	u32 event_buffer_size;
+	DECLARE_KFIFO_PTR(events, struct gpio_v2_line_event);
+	atomic_t seqno;
 	struct line lines[];
 };
 
@@ -436,12 +470,151 @@ struct linereq {
 	(GPIO_V2_LINE_FLAG_OPEN_DRAIN | \
 	 GPIO_V2_LINE_FLAG_OPEN_SOURCE)
 
+#define GPIO_V2_LINE_EDGE_FLAGS \
+	(GPIO_V2_LINE_FLAG_EDGE_RISING | \
+	 GPIO_V2_LINE_FLAG_EDGE_FALLING)
+
 #define GPIO_V2_LINE_VALID_FLAGS \
 	(GPIO_V2_LINE_FLAG_ACTIVE_LOW | \
 	 GPIO_V2_LINE_DIRECTION_FLAGS | \
 	 GPIO_V2_LINE_DRIVE_FLAGS | \
+	 GPIO_V2_LINE_EDGE_FLAGS | \
 	 GPIO_V2_LINE_BIAS_FLAGS)
 
+static void linereq_put_event(struct linereq *lr,
+			      struct gpio_v2_line_event *le)
+{
+	bool overflow = false;
+
+	spin_lock(&lr->wait.lock);
+	if (kfifo_is_full(&lr->events)) {
+		overflow = true;
+		kfifo_skip(&lr->events);
+	}
+	kfifo_in(&lr->events, le, 1);
+	spin_unlock(&lr->wait.lock);
+	if (!overflow)
+		wake_up_poll(&lr->wait, EPOLLIN);
+	else
+		pr_debug_ratelimited("event FIFO is full - event dropped\n");
+}
+
+static irqreturn_t edge_irq_thread(int irq, void *p)
+{
+	struct line *line = p;
+	struct linereq *lr = line->req;
+	struct gpio_v2_line_event le;
+
+	/* Do not leak kernel stack to userspace */
+	memset(&le, 0, sizeof(le));
+
+	if (line->timestamp_ns) {
+		le.timestamp_ns = line->timestamp_ns;
+	} else {
+		/*
+		 * We may be running from a nested threaded interrupt in
+		 * which case we didn't get the timestamp from
+		 * edge_irq_handler().
+		 */
+		le.timestamp_ns = ktime_get_ns();
+		if (lr->num_lines != 1)
+			line->req_seqno = atomic_inc_return(&lr->seqno);
+	}
+	line->timestamp_ns = 0;
+
+	if (line->eflags == (GPIO_V2_LINE_FLAG_EDGE_RISING |
+			     GPIO_V2_LINE_FLAG_EDGE_FALLING)) {
+		int level = gpiod_get_value_cansleep(line->desc);
+
+		if (level)
+			/* Emit low-to-high event */
+			le.id = GPIO_V2_LINE_EVENT_RISING_EDGE;
+		else
+			/* Emit high-to-low event */
+			le.id = GPIO_V2_LINE_EVENT_FALLING_EDGE;
+	} else if (line->eflags == GPIO_V2_LINE_FLAG_EDGE_RISING) {
+		/* Emit low-to-high event */
+		le.id = GPIO_V2_LINE_EVENT_RISING_EDGE;
+	} else if (line->eflags == GPIO_V2_LINE_FLAG_EDGE_FALLING) {
+		/* Emit high-to-low event */
+		le.id = GPIO_V2_LINE_EVENT_FALLING_EDGE;
+	} else {
+		return IRQ_NONE;
+	}
+	line->line_seqno++;
+	le.line_seqno = line->line_seqno;
+	le.seqno = (lr->num_lines == 1) ? le.line_seqno : line->req_seqno;
+	le.offset = gpio_chip_hwgpio(line->desc);
+
+	linereq_put_event(lr, &le);
+
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t edge_irq_handler(int irq, void *p)
+{
+	struct line *line = p;
+	struct linereq *lr = line->req;
+
+	/*
+	 * Just store the timestamp in hardirq context so we get it as
+	 * close in time as possible to the actual event.
+	 */
+	line->timestamp_ns = ktime_get_ns();
+
+	if (lr->num_lines != 1)
+		line->req_seqno = atomic_inc_return(&lr->seqno);
+
+	return IRQ_WAKE_THREAD;
+}
+
+static void edge_detector_stop(struct line *line)
+{
+	if (line->irq) {
+		free_irq(line->irq, line);
+		line->irq = 0;
+	}
+}
+
+static int edge_detector_setup(struct line *line,
+			       u64 eflags)
+{
+	unsigned long irqflags = 0;
+	int irq, ret;
+
+	if (eflags && !kfifo_initialized(&line->req->events)) {
+		ret = kfifo_alloc(&line->req->events,
+				  line->req->event_buffer_size, GFP_KERNEL);
+		if (ret)
+			return ret;
+	}
+	line->eflags = eflags;
+
+	if (!eflags)
+		return 0;
+
+	irq = gpiod_to_irq(line->desc);
+	if (irq < 0)
+		return -ENXIO;
+
+	if (eflags & GPIO_V2_LINE_FLAG_EDGE_RISING)
+		irqflags |= test_bit(FLAG_ACTIVE_LOW, &line->desc->flags) ?
+			IRQF_TRIGGER_FALLING : IRQF_TRIGGER_RISING;
+	if (eflags & GPIO_V2_LINE_FLAG_EDGE_FALLING)
+		irqflags |= test_bit(FLAG_ACTIVE_LOW, &line->desc->flags) ?
+			IRQF_TRIGGER_RISING : IRQF_TRIGGER_FALLING;
+	irqflags |= IRQF_ONESHOT;
+
+	/* Request a thread to read the events */
+	ret = request_threaded_irq(irq, edge_irq_handler, edge_irq_thread,
+				   irqflags, line->req->label, line);
+	if (ret)
+		return ret;
+
+	line->irq = irq;
+	return 0;
+}
+
 static u64 gpio_v2_line_config_flags(struct gpio_v2_line_config *lc,
 				     unsigned int line_idx)
 {
@@ -484,6 +657,11 @@ static int gpio_v2_line_flags_validate(u64 flags)
 	    (flags & GPIO_V2_LINE_FLAG_OUTPUT))
 		return -EINVAL;
 
+	/* Edge detection requires explicit input. */
+	if ((flags & GPIO_V2_LINE_EDGE_FLAGS) &&
+	    !(flags & GPIO_V2_LINE_FLAG_INPUT))
+		return -EINVAL;
+
 	/*
 	 * Do not allow OPEN_SOURCE and OPEN_DRAIN flags in a single
 	 * request. If the hardware actually supports enabling both at the
@@ -547,6 +725,11 @@ static void gpio_v2_line_config_flags_to_desc_flags(u64 flags,
 	else if (flags & GPIO_V2_LINE_FLAG_INPUT)
 		clear_bit(FLAG_IS_OUT, flagsp);
 
+	assign_bit(FLAG_EDGE_RISING, flagsp,
+		   flags & GPIO_V2_LINE_FLAG_EDGE_RISING);
+	assign_bit(FLAG_EDGE_FALLING, flagsp,
+		   flags & GPIO_V2_LINE_FLAG_EDGE_FALLING);
+
 	assign_bit(FLAG_OPEN_DRAIN, flagsp,
 		   flags & GPIO_V2_LINE_FLAG_OPEN_DRAIN);
 	assign_bit(FLAG_OPEN_SOURCE, flagsp,
@@ -636,14 +819,85 @@ static long linereq_ioctl_compat(struct file *file, unsigned int cmd,
 }
 #endif
 
+static __poll_t linereq_poll(struct file *file,
+			    struct poll_table_struct *wait)
+{
+	struct linereq *lr = file->private_data;
+	__poll_t events = 0;
+
+	poll_wait(file, &lr->wait, wait);
+
+	if (!kfifo_is_empty_spinlocked_noirqsave(&lr->events,
+						 &lr->wait.lock))
+		events = EPOLLIN | EPOLLRDNORM;
+
+	return events;
+}
+
+static ssize_t linereq_read(struct file *file,
+			    char __user *buf,
+			    size_t count,
+			    loff_t *f_ps)
+{
+	struct linereq *lr = file->private_data;
+	struct gpio_v2_line_event le;
+	ssize_t bytes_read = 0;
+	int ret;
+
+	if (count < sizeof(le))
+		return -EINVAL;
+
+	do {
+		spin_lock(&lr->wait.lock);
+		if (kfifo_is_empty(&lr->events)) {
+			if (bytes_read) {
+				spin_unlock(&lr->wait.lock);
+				return bytes_read;
+			}
+
+			if (file->f_flags & O_NONBLOCK) {
+				spin_unlock(&lr->wait.lock);
+				return -EAGAIN;
+			}
+
+			ret = wait_event_interruptible_locked(lr->wait,
+					!kfifo_is_empty(&lr->events));
+			if (ret) {
+				spin_unlock(&lr->wait.lock);
+				return ret;
+			}
+		}
+
+		ret = kfifo_out(&lr->events, &le, 1);
+		spin_unlock(&lr->wait.lock);
+		if (ret != 1) {
+			/*
+			 * This should never happen - we were holding the
+			 * lock from the moment we learned the fifo is no
+			 * longer empty until now.
+			 */
+			ret = -EIO;
+			break;
+		}
+
+		if (copy_to_user(buf + bytes_read, &le, sizeof(le)))
+			return -EFAULT;
+		bytes_read += sizeof(le);
+	} while (count >= bytes_read + sizeof(le));
+
+	return bytes_read;
+}
+
 static void linereq_free(struct linereq *lr)
 {
 	unsigned int i;
 
 	for (i = 0; i < lr->num_lines; i++) {
+		edge_detector_stop(&lr->lines[i]);
 		if (lr->lines[i].desc)
 			gpiod_free(lr->lines[i].desc);
 	}
+	kfifo_free(&lr->events);
 	kfree(lr->label);
 	put_device(&lr->gdev->dev);
 	kfree(lr);
@@ -659,6 +913,8 @@ static int linereq_release(struct inode *inode, struct file *file)
 
 static const struct file_operations line_fileops = {
 	.release = linereq_release,
+	.read = linereq_read,
+	.poll = linereq_poll,
 	.owner = THIS_MODULE,
 	.llseek = noop_llseek,
 	.unlocked_ioctl = linereq_ioctl,
@@ -698,6 +954,9 @@ static int linereq_create(struct gpio_device *gdev, void __user *ip)
 	lr->gdev = gdev;
 	get_device(&gdev->dev);
 
+	for (i = 0; i < ulr.num_lines; i++)
+		lr->lines[i].req = lr;
+
 	/* Make sure this is terminated */
 	ulr.consumer[sizeof(ulr.consumer)-1] = '\0';
 	if (strlen(ulr.consumer)) {
@@ -709,6 +968,14 @@ static int linereq_create(struct gpio_device *gdev, void __user *ip)
 		}
 	}
 
+	init_waitqueue_head(&lr->wait);
+	lr->event_buffer_size = ulr.event_buffer_size;
+	if (lr->event_buffer_size == 0)
+		lr->event_buffer_size = ulr.num_lines * 16;
+	else if (lr->event_buffer_size > GPIO_V2_LINES_MAX * 16)
+		lr->event_buffer_size = GPIO_V2_LINES_MAX * 16;
+
+	atomic_set(&lr->seqno, 0);
 	lr->num_lines = ulr.num_lines;
 
 	/* Request each GPIO */
@@ -747,6 +1014,11 @@ static int linereq_create(struct gpio_device *gdev, void __user *ip)
 			ret = gpiod_direction_input(desc);
 			if (ret)
 				goto out_free_linereq;
+
+			ret = edge_detector_setup(&lr->lines[i],
+					flags & GPIO_V2_LINE_EDGE_FLAGS);
+			if (ret)
+				goto out_free_linereq;
 		}
 
 		blocking_notifier_call_chain(&desc->gdev->notifier,
@@ -1268,6 +1540,11 @@ static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
 	if (test_bit(FLAG_PULL_UP, &desc->flags))
 		info->flags |= GPIO_V2_LINE_FLAG_BIAS_PULL_UP;
 
+	if (test_bit(FLAG_EDGE_RISING, &desc->flags))
+		info->flags |= GPIO_V2_LINE_FLAG_EDGE_RISING;
+	if (test_bit(FLAG_EDGE_FALLING, &desc->flags))
+		info->flags |= GPIO_V2_LINE_FLAG_EDGE_FALLING;
+
 	spin_unlock_irqrestore(&gpio_lock, flags);
 }
 
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index dfcff5d24b18..aa20481e9452 100644
--- a/drivers/gpio/gpiolib.c
+++ b/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;
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index 6709f79c02dd..39b356160937 100644
--- a/drivers/gpio/gpiolib.h
+++ b/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;
-- 
2.28.0