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leds: trigger: pattern: Add support for hrtimer

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Currently, led pattern trigger uses timer_list to schedule brightness
changing. As we know from timer_list API [1], it's not accurate to
milliseconds and depends on HZ granularity.

Example:
"0 10 0 0 50 10 50 0 100 10 100 0 150 10 150 0 200 10 200 0 250 10 250 0",
we expect it to be 60ms long, but it can actually be up to ~120ms
(add ~10ms for each pattern when HZ == 100).

But sometimes, userspace needs time accurate led patterns to make sure
that pattern will be executed during expected time slot.
To achieve this goal the patch introduces optional hrtimer usage for
led trigger pattern, because hrtimer is microseconds accurate timer.

[1]: kernel/time/timer.c#L104

Signed-off-by: Martin Kurbanov <mmkurbanov@salutedevices.com>
Link: https://lore.kernel.org/r/20240416201847.357099-1-mmkurbanov@salutedevices.com
Signed-off-by: Lee Jones <lee@kernel.org>
This commit is contained in:
Martin Kurbanov
2024-04-16 23:18:05 +03:00
committed by Lee Jones
parent fd05e36986
commit aa172ba739
2 changed files with 113 additions and 23 deletions
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10
Documentation/ABI/testing/sysfs-class-led-trigger-pattern
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@@ -12,6 +12,16 @@ Description:
The exact format is described in:
Documentation/devicetree/bindings/leds/leds-trigger-pattern.txt
What: /sys/class/leds/<led>/hr_pattern
Date: April 2024
Description:
Specify a software pattern for the LED, that supports altering
the brightness for the specified duration with one software
timer. It can do gradual dimming and step change of brightness.
Unlike the /sys/class/leds/<led>/pattern, this attribute runs
a pattern on high-resolution timer (hrtimer).
What: /sys/class/leds/<led>/hw_pattern
Date: September 2018
KernelVersion: 4.20