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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
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12
include/uapi/linux/gpio.h
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@ -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;