diff mbox series

[1/3] gpiolib: cdev: allow edge event timestamps to be configured as REALTIME

Message ID 20201014062740.78977-2-warthog618@gmail.com
State Superseded
Headers show
Series gpiolib: cdev: allow edge event timestamps to be configured as REALTIME | expand

Commit Message

Kent Gibson Oct. 14, 2020, 6:27 a.m. UTC
Using CLOCK_REALTIME as the source for event timestamps is crucial for
some specific applications, particularly those requiring timetamps
relative to a PTP clock, so provide an option to switch the event
timestamp source from the default CLOCK_MONOTONIC to CLOCK_REALTIME.

Note that CLOCK_REALTIME was the default source clock for GPIO until
Linux 5.7 when it was changed to CLOCK_MONOTONIC due to issues with the
shifting of the realtime clock.
Providing this option maintains the CLOCK_MONOTONIC as the default,
while also providing a path forward for those dependent on the pre-5.7
behaviour.

Suggested-by: Jack Winch <sunt.un.morcov@gmail.com>
Signed-off-by: Kent Gibson <warthog618@gmail.com>
---
 drivers/gpio/gpiolib-cdev.c | 21 ++++++++++++++++++---
 drivers/gpio/gpiolib.h      |  1 +
 include/uapi/linux/gpio.h   | 12 +++++++++---
 3 files changed, 28 insertions(+), 6 deletions(-)

Comments

Kent Gibson Oct. 14, 2020, 4:17 p.m. UTC | #1
On Wed, Oct 14, 2020 at 02:27:38PM +0800, Kent Gibson wrote:
> Using CLOCK_REALTIME as the source for event timestamps is crucial for
> some specific applications, particularly those requiring timetamps
> relative to a PTP clock, so provide an option to switch the event
> timestamp source from the default CLOCK_MONOTONIC to CLOCK_REALTIME.
> 
[snip]
>  
>  static void linereq_put_event(struct linereq *lr,
> @@ -535,6 +536,14 @@ static void linereq_put_event(struct linereq *lr,
>  		pr_debug_ratelimited("event FIFO is full - event dropped\n");
>  }
>  
> +static unsigned long line_event_timestamp(struct line *line)
> +{
> +	if (test_bit(FLAG_EVENT_CLOCK_REALTIME, &line->desc->flags))
> +		return ktime_get_real_ns();
> +
> +	return ktime_get_ns();
> +
> +}

One minor hitch - that should be returning u64, not unsigned long,
or the time gets reduced to 32bit on 32bit platforms.

It's getting late though, so I'll send out an update tomorrow.

Cheers,
Kent.
diff mbox series

Patch

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index 678de9264617..147626a78a92 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -515,6 +515,7 @@  struct linereq {
 	 GPIO_V2_LINE_DIRECTION_FLAGS | \
 	 GPIO_V2_LINE_DRIVE_FLAGS | \
 	 GPIO_V2_LINE_EDGE_FLAGS | \
+	 GPIO_V2_LINE_FLAG_EVENT_CLOCK_REALTIME | \
 	 GPIO_V2_LINE_BIAS_FLAGS)
 
 static void linereq_put_event(struct linereq *lr,
@@ -535,6 +536,14 @@  static void linereq_put_event(struct linereq *lr,
 		pr_debug_ratelimited("event FIFO is full - event dropped\n");
 }
 
+static unsigned long line_event_timestamp(struct line *line)
+{
+	if (test_bit(FLAG_EVENT_CLOCK_REALTIME, &line->desc->flags))
+		return ktime_get_real_ns();
+
+	return ktime_get_ns();
+
+}
 static irqreturn_t edge_irq_thread(int irq, void *p)
 {
 	struct line *line = p;
@@ -553,7 +562,7 @@  static irqreturn_t edge_irq_thread(int irq, void *p)
 		 * which case we didn't get the timestamp from
 		 * edge_irq_handler().
 		 */
-		le.timestamp_ns = ktime_get_ns();
+		le.timestamp_ns = line_event_timestamp(line);
 		if (lr->num_lines != 1)
 			line->req_seqno = atomic_inc_return(&lr->seqno);
 	}
@@ -598,7 +607,7 @@  static irqreturn_t edge_irq_handler(int irq, void *p)
 	 * 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();
+	line->timestamp_ns = line_event_timestamp(line);
 
 	if (lr->num_lines != 1)
 		line->req_seqno = atomic_inc_return(&lr->seqno);
@@ -673,7 +682,7 @@  static void debounce_work_func(struct work_struct *work)
 	memset(&le, 0, sizeof(le));
 
 	lr = line->req;
-	le.timestamp_ns = ktime_get_ns();
+	le.timestamp_ns = line_event_timestamp(line);
 	le.offset = gpio_chip_hwgpio(line->desc);
 	line->line_seqno++;
 	le.line_seqno = line->line_seqno;
@@ -977,6 +986,9 @@  static void gpio_v2_line_config_flags_to_desc_flags(u64 flags,
 		   flags & GPIO_V2_LINE_FLAG_BIAS_PULL_DOWN);
 	assign_bit(FLAG_BIAS_DISABLE, flagsp,
 		   flags & GPIO_V2_LINE_FLAG_BIAS_DISABLED);
+
+	assign_bit(FLAG_EVENT_CLOCK_REALTIME, flagsp,
+		   flags & GPIO_V2_LINE_FLAG_EVENT_CLOCK_REALTIME);
 }
 
 static long linereq_get_values(struct linereq *lr, void __user *ip)
@@ -1940,6 +1952,9 @@  static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
 	if (test_bit(FLAG_EDGE_FALLING, &desc->flags))
 		info->flags |= GPIO_V2_LINE_FLAG_EDGE_FALLING;
 
+	if (test_bit(FLAG_EVENT_CLOCK_REALTIME, &desc->flags))
+		info->flags |= GPIO_V2_LINE_FLAG_EVENT_CLOCK_REALTIME;
+
 	debounce_period_us = READ_ONCE(desc->debounce_period_us);
 	if (debounce_period_us) {
 		info->attrs[num_attrs].id = GPIO_V2_LINE_ATTR_ID_DEBOUNCE;
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index b674b5bb980e..2f228ffe8320 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -116,6 +116,7 @@  struct gpio_desc {
 #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 */
+#define FLAG_EVENT_CLOCK_REALTIME	18 /* GPIO CDEV reports REALTIME timestamps in events */
 
 	/* Connection label */
 	const char		*label;
diff --git a/include/uapi/linux/gpio.h b/include/uapi/linux/gpio.h
index 2072c260f5d0..e4eb0b8c5cf9 100644
--- a/include/uapi/linux/gpio.h
+++ b/include/uapi/linux/gpio.h
@@ -65,6 +65,7 @@  struct gpiochip_info {
  * @GPIO_V2_LINE_FLAG_BIAS_PULL_UP: line has pull-up bias enabled
  * @GPIO_V2_LINE_FLAG_BIAS_PULL_DOWN: line has pull-down bias enabled
  * @GPIO_V2_LINE_FLAG_BIAS_DISABLED: line has bias disabled
+ * @GPIO_V2_LINE_FLAG_EVENT_CLOCK_REALTIME: line events contain REALTIME timestamps
  */
 enum gpio_v2_line_flag {
 	GPIO_V2_LINE_FLAG_USED			= _BITULL(0),
@@ -78,6 +79,7 @@  enum gpio_v2_line_flag {
 	GPIO_V2_LINE_FLAG_BIAS_PULL_UP		= _BITULL(8),
 	GPIO_V2_LINE_FLAG_BIAS_PULL_DOWN	= _BITULL(9),
 	GPIO_V2_LINE_FLAG_BIAS_DISABLED		= _BITULL(10),
+	GPIO_V2_LINE_FLAG_EVENT_CLOCK_REALTIME	= _BITULL(11),
 };
 
 /**
@@ -270,9 +272,6 @@  enum gpio_v2_line_event_id {
 /**
  * struct gpio_v2_line_event - The actual event being pushed to userspace
  * @timestamp_ns: best estimate of time of event occurrence, in nanoseconds.
- * The @timestamp_ns is read from %CLOCK_MONOTONIC and is intended to allow
- * the accurate measurement of the time between events. It does not provide
- * the wall-clock time.
  * @id: event identifier with value from &enum gpio_v2_line_event_id
  * @offset: the offset of the line that triggered the event
  * @seqno: the sequence number for this event in the sequence of events for
@@ -280,6 +279,13 @@  enum gpio_v2_line_event_id {
  * @line_seqno: the sequence number for this event in the sequence of
  * events on this particular line
  * @padding: reserved for future use
+ *
+ * By default the @timestamp_ns is read from %CLOCK_MONOTONIC and is
+ * intended to allow the accurate measurement of the time between events.
+ * It does not provide the wall-clock time.
+ *
+ * If the %GPIO_V2_LINE_FLAG_EVENT_CLOCK_REALTIME flag is set then the
+ * @timestamp_ns is read from %CLOCK_REALTIME.
  */
 struct gpio_v2_line_event {
 	__aligned_u64 timestamp_ns;