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gpiolib: cdev: allow edge event timestamps to be configured as REALTIME

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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>
Link: https://lore.kernel.org/r/20201014231158.34117-2-warthog618@gmail.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
This commit is contained in:
Kent Gibson 2020-10-15 07:11:56 +08:00 committed by Linus Walleij
parent 93224edf0b
commit 26d060e47e
3 changed files with 28 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
drivers/gpio/gpiolib-cdev.c
View File

@ -509,6 +509,7 @@ 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,
@ -529,6 +530,14 @@ 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;
@ -546,7 +555,7 @@ 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);
}
@ -590,7 +599,7 @@ 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);
@ -663,7 +672,7 @@ 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;
@ -967,6 +976,9 @@ 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)
@ -1930,6 +1942,9 @@ 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;

1
drivers/gpio/gpiolib.h
View File

@ -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;

12
include/uapi/linux/gpio.h
View File

@ -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;