[PATCH v4 09/20] gpiolib: cdev: support edge detection for uAPI v2

From: Kent Gibson
Date: Thu Aug 13 2020 - 23:04:34 EST

Add support for edge detection to lines requested using
GPIO_V2_GET_LINE_IOCTL.

Signed-off-by: Kent Gibson <warthog618@xxxxxxxxx>
---

The edge_detector implementation is based on the v1 lineevent implementation.

drivers/gpio/gpiolib-cdev.c | 316 +++++++++++++++++++++++++++++++++++-
drivers/gpio/gpiolib.c | 2 +
drivers/gpio/gpiolib.h | 2 +
3 files changed, 319 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index 28273f3105d3..1d42a01f5414 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -382,11 +382,43 @@ static int linehandle_create(struct gpio_device *gdev, void __user *ip)
}
#endif /* CONFIG_GPIO_CDEV_V1 */

+/**
+ * struct edge_detector - contains the state of a line edge detector
+ * @line: the corresponding line request
+ * @irq: the interrupt triggered in response to events on this GPIO
+ * @flags: the flags, GPIO_V2_LINE_FLAG_EDGE_RISING and/or
+ * GPIO_V2_LINE_FLAG_EDGE_FALLING, indicating the edge detection applied
+ * @timestamp: cache for the timestamp storing it between hardirq and IRQ
+ * thread, used to bring the timestamp close to the actual event
+ * @seqno: the seqno for the current edge event in the sequence of events
+ * for the corresponding line request. Ths is drawn from the @line.
+ * @line_seqno: the seqno for the current edge event in the sequence of
+ * events for this line.
+ */
+struct edge_detector {
+ struct line *line;
+ unsigned int irq;
+ u64 flags;
+ /*
+ * timestamp and seqno are shared by edge_irq_handler() and
+ * edge_irq_thread() which are themselves mutually exclusive.
+ */
+ u64 timestamp;
+ u32 seqno;
+ u32 line_seqno;
+};
+
/**
* struct line - contains the state of a userspace line request
* @gdev: the GPIO device the line request pertains to
* @label: consumer label used to tag descriptors
* @num_descs: the number of descriptors held in the descs array
+ * @wait: wait queue that handles blocking reads of 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_descs is 1, as
+ * the line_seqno is then the same and is cheaper to calculate.
+ * @edets: an array of edge detectors, of size @num_descs
* @descs: the GPIO descriptors held by this line request, with @num_descs
* elements.
*/
@@ -394,9 +426,146 @@ struct line {
struct gpio_device *gdev;
const char *label;
u32 num_descs;
+ wait_queue_head_t wait;
+ DECLARE_KFIFO_PTR(events, struct gpio_v2_line_event);
+ atomic_t seqno;
+ struct edge_detector *edets;
struct gpio_desc *descs[];
};

+static inline struct gpio_desc *edge_detector_desc(
+ const struct edge_detector *edet)
+{
+ return edet->line->descs[edet - &edet->line->edets[0]];
+}
+
+static irqreturn_t edge_irq_thread(int irq, void *p)
+{
+ struct edge_detector *edet = p;
+ struct line *line = edet->line;
+ struct gpio_desc *desc = edge_detector_desc(edet);
+ struct gpio_v2_line_event le;
+ int ret;
+
+ /* Do not leak kernel stack to userspace */
+ memset(&le, 0, sizeof(le));
+
+ /*
+ * We may be running from a nested threaded interrupt in which case
+ * we didn't get the timestamp from edge_irq_handler().
+ */
+ if (!edet->timestamp) {
+ le.timestamp = ktime_get_ns();
+ if (line->num_descs != 1)
+ edet->seqno = atomic_inc_return(&line->seqno);
+ } else {
+ le.timestamp = edet->timestamp;
+ }
+ edet->timestamp = 0;
+
+ if (edet->flags == (GPIO_V2_LINE_FLAG_EDGE_RISING |
+ GPIO_V2_LINE_FLAG_EDGE_FALLING)) {
+ int level = gpiod_get_value_cansleep(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 (edet->flags == GPIO_V2_LINE_FLAG_EDGE_RISING) {
+ /* Emit low-to-high event */
+ le.id = GPIO_V2_LINE_EVENT_RISING_EDGE;
+ } else if (edet->flags == GPIO_V2_LINE_FLAG_EDGE_FALLING) {
+ /* Emit high-to-low event */
+ le.id = GPIO_V2_LINE_EVENT_FALLING_EDGE;
+ } else {
+ return IRQ_NONE;
+ }
+ edet->line_seqno++;
+ le.line_seqno = edet->line_seqno;
+ le.seqno = (line->num_descs == 1) ? le.line_seqno : edet->seqno;
+ le.offset = gpio_chip_hwgpio(desc);
+
+ ret = kfifo_in_spinlocked_noirqsave(&line->events, &le,
+ 1, &line->wait.lock);
+ if (ret)
+ wake_up_poll(&line->wait, EPOLLIN);
+ else
+ pr_debug_ratelimited("event FIFO is full - event dropped\n");
+
+ return IRQ_HANDLED;
+}
+
+static irqreturn_t edge_irq_handler(int irq, void *p)
+{
+ struct edge_detector *edet = p;
+ struct line *line = edet->line;
+
+ /*
+ * Just store the timestamp in hardirq context so we get it as
+ * close in time as possible to the actual event.
+ */
+ edet->timestamp = ktime_get_ns();
+
+ if (line->num_descs != 1)
+ edet->seqno = atomic_inc_return(&line->seqno);
+
+ return IRQ_WAKE_THREAD;
+}
+
+static int edge_detector_start(struct edge_detector *edet)
+{
+ int ret, irq, irqflags = 0;
+ struct gpio_desc *desc;
+
+ desc = edge_detector_desc(edet);
+ irq = gpiod_to_irq(desc);
+
+ if (irq <= 0)
+ return -ENODEV;
+
+ edet->seqno = 0;
+ edet->line_seqno = 0;
+
+ if (edet->flags & GPIO_V2_LINE_FLAG_EDGE_RISING)
+ irqflags |= test_bit(FLAG_ACTIVE_LOW, &desc->flags) ?
+ IRQF_TRIGGER_FALLING : IRQF_TRIGGER_RISING;
+ if (edet->flags & GPIO_V2_LINE_FLAG_EDGE_FALLING)
+ irqflags |= test_bit(FLAG_ACTIVE_LOW, &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,
+ edet->line->label,
+ edet);
+ if (ret)
+ return ret;
+
+ edet->irq = irq;
+ return 0;
+}
+
+static void edge_detector_stop(struct edge_detector *edet)
+{
+ if (edet->irq) {
+ free_irq(edet->irq, edet);
+ edet->irq = 0;
+ }
+}
+
+static int edge_detector_setup(struct edge_detector *edet,
+ struct gpio_v2_line_config *lc)
+{
+ if (edet->flags)
+ return edge_detector_start(edet);
+ return 0;
+}
+
#define GPIO_V2_LINE_BIAS_FLAGS \
(GPIO_V2_LINE_FLAG_BIAS_PULL_UP | \
GPIO_V2_LINE_FLAG_BIAS_PULL_DOWN | \
@@ -410,10 +579,15 @@ struct line {
(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 u64 gpio_v2_line_config_flags(struct gpio_v2_line_config *lc,
@@ -430,6 +604,21 @@ static u64 gpio_v2_line_config_flags(struct gpio_v2_line_config *lc,
return lc->flags;
}

+static int gpio_v2_line_config_has_edge_detection(struct gpio_v2_line_config *lc)
+{
+ int i;
+
+ if (lc->flags & GPIO_V2_LINE_EDGE_FLAGS)
+ return 1;
+
+ for (i = 0; i < lc->num_attrs; i--) {
+ if ((lc->attrs[i].attr.id == GPIO_V2_LINE_ATTR_ID_FLAGS) &&
+ (lc->attrs[i].attr.flags & GPIO_V2_LINE_EDGE_FLAGS))
+ return 1;
+ }
+ return 0;
+}
+
static int gpio_v2_line_config_output_value(struct gpio_v2_line_config *lc,
int line_idx)
{
@@ -458,6 +647,11 @@ 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 & OPEN_DRAIN flags in a single request. If
* the hardware actually supports enabling both at the same time the
@@ -518,6 +712,10 @@ static void gpio_v2_line_config_flags_to_desc_flags(u64 flags,
set_bit(FLAG_IS_OUT, flagsp);
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,
@@ -605,14 +803,87 @@ static long line_ioctl_compat(struct file *file, unsigned int cmd,
}
#endif

+static __poll_t line_poll(struct file *file,
+ struct poll_table_struct *wait)
+{
+ struct line *line = file->private_data;
+ __poll_t events = 0;
+
+ poll_wait(file, &line->wait, wait);
+
+ if (!kfifo_is_empty_spinlocked_noirqsave(&line->events,
+ &line->wait.lock))
+ events = EPOLLIN | EPOLLRDNORM;
+
+ return events;
+}
+
+static ssize_t line_read(struct file *file,
+ char __user *buf,
+ size_t count,
+ loff_t *f_ps)
+{
+ struct line *line = 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(&line->wait.lock);
+ if (kfifo_is_empty(&line->events)) {
+ if (bytes_read) {
+ spin_unlock(&line->wait.lock);
+ return bytes_read;
+ }
+
+ if (file->f_flags & O_NONBLOCK) {
+ spin_unlock(&line->wait.lock);
+ return -EAGAIN;
+ }
+
+ ret = wait_event_interruptible_locked(line->wait,
+ !kfifo_is_empty(&line->events));
+ if (ret) {
+ spin_unlock(&line->wait.lock);
+ return ret;
+ }
+ }
+
+ ret = kfifo_out(&line->events, &le, 1);
+ spin_unlock(&line->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 line_free(struct line *line)
{
int i;

for (i = 0; i < line->num_descs; i++) {
+ if (line->edets)
+ edge_detector_stop(&line->edets[i]);
if (line->descs[i])
gpiod_free(line->descs[i]);
}
+ kfifo_free(&line->events);
+ kfree(line->edets);
kfree(line->label);
put_device(&line->gdev->dev);
kfree(line);
@@ -628,6 +899,8 @@ static int line_release(struct inode *inode, struct file *file)

static const struct file_operations line_fileops = {
.release = line_release,
+ .read = line_read,
+ .poll = line_poll,
.owner = THIS_MODULE,
.llseek = noop_llseek,
.unlocked_ioctl = line_ioctl,
@@ -641,7 +914,7 @@ static int line_create(struct gpio_device *gdev, void __user *ip)
struct gpio_v2_line_request lr;
struct line *line;
struct file *file;
- int fd, i, ret;
+ int fd, i, ret, size, has_edge_detection;
struct gpio_v2_line_config *lc;
unsigned long flags;

@@ -658,6 +931,11 @@ static int line_create(struct gpio_device *gdev, void __user *ip)
if (ret)
return ret;

+ /* event_buffer_size only valid with edge detection */
+ has_edge_detection = gpio_v2_line_config_has_edge_detection(lc);
+ if (lr.event_buffer_size && !has_edge_detection)
+ return -EINVAL;
+
line = kzalloc(struct_size(line, descs, lr.num_lines),
GFP_KERNEL);
if (!line)
@@ -666,6 +944,16 @@ static int line_create(struct gpio_device *gdev, void __user *ip)
line->gdev = gdev;
get_device(&gdev->dev);

+ line->edets = kcalloc(lr.num_lines, sizeof(*line->edets),
+ GFP_KERNEL);
+ if (!line->edets) {
+ ret = -ENOMEM;
+ goto out_free_line;
+ }
+
+ for (i = 0; i < lr.num_lines; i++)
+ line->edets[i].line = line;
+
/* Make sure this is terminated */
lr.consumer[sizeof(lr.consumer)-1] = '\0';
if (strlen(lr.consumer)) {
@@ -676,6 +964,21 @@ static int line_create(struct gpio_device *gdev, void __user *ip)
}
}

+ init_waitqueue_head(&line->wait);
+ if (has_edge_detection) {
+ size = lr.event_buffer_size;
+
+ if (size > GPIO_V2_LINES_MAX*16)
+ size = GPIO_V2_LINES_MAX*16;
+ else if (size == 0)
+ size = lr.num_lines*16;
+
+ ret = kfifo_alloc(&line->events, size, GFP_KERNEL);
+ if (ret)
+ goto out_free_line;
+ }
+
+ atomic_set(&line->seqno, 0);
line->num_descs = lr.num_lines;

/* Request each GPIO */
@@ -714,6 +1017,10 @@ static int line_create(struct gpio_device *gdev, void __user *ip)
ret = gpiod_direction_input(desc);
if (ret)
goto out_free_line;
+ line->edets[i].flags = flags & GPIO_V2_LINE_EDGE_FLAGS;
+ ret = edge_detector_setup(&line->edets[i], lc);
+ if (ret)
+ goto out_free_line;
}

blocking_notifier_call_chain(&desc->gdev->notifier,
@@ -1237,6 +1544,13 @@ 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;
+
+ info->num_attrs = 0;
+
spin_unlock_irqrestore(&gpio_lock, flags);
}

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 80137c1b3cdc..e4c81dca7f8b 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2041,6 +2041,8 @@ 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