[PATCH v2 1/3] gpiolib: cdev: allow edge event timestamps to be configured as REALTIME
From: Kent Gibson
Date: Wed Oct 14 2020 - 21:39:48 EST
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@xxxxxxxxx>
Signed-off-by: Kent Gibson <warthog618@xxxxxxxxx>
---
drivers/gpio/gpiolib-cdev.c | 21 ++++++++++++++++++---
drivers/gpio/gpiolib.h | 1 +
include/uapi/linux/gpio.h | 12 +++++++++---
3 files changed, 28 insertions(+), 6 deletions(-)
diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index 678de9264617..ea787eb3810d 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 u64 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;
--
2.28.0