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leds: class: Add new optional brightness_hw_changed attribute

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Some LEDs may have their brightness level changed autonomously
(outside of kernel control) by hardware / firmware. This commit
adds support for an optional brightness_hw_changed attribute to
signal such changes to userspace (if a driver can detect them):

What:		/sys/class/leds/<led>/brightness_hw_changed
Date:		January 2017
KernelVersion:	4.11
Description:
		Last hardware set brightness level for this LED. Some LEDs
		may be changed autonomously by hardware/firmware. Only LEDs
		where this happens and the driver can detect this, will
		have this file.

		This file supports poll() to detect when the hardware
		changes the brightness.

		Reading this file will return the last brightness level set
		by the hardware, this may be different from the current
		brightness.

Drivers which want to support this, simply add LED_BRIGHT_HW_CHANGED to
their flags field and call led_classdev_notify_brightness_hw_changed()
with the hardware set brightness when they detect a hardware / firmware
triggered brightness change.

Signed-off-by: Hans de Goede <[email protected]>
Acked-by: Pavel Machek <[email protected]>
Signed-off-by: Jacek Anaszewski <[email protected]>
This commit is contained in:
Hans de Goede 2017-01-29 14:42:52 +01:00 • committed by Jacek Anaszewski
commit 0cb8eb30d4
5 changed files with 132 additions and 0 deletions
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15
Documentation/leds/leds-class.txt
View file

@ -65,6 +65,21 @@ LED subsystem core exposes following API for setting brightness:
blinking, returns -EBUSY if software blink fallback is enabled.
LED registration API
====================
A driver wanting to register a LED classdev for use by other drivers /
userspace needs to allocate and fill a led_classdev struct and then call
[devm_]led_classdev_register. If the non devm version is used the driver
must call led_classdev_unregister from its remove function before
free-ing the led_classdev struct.
If the driver can detect hardware initiated brightness changes and thus
wants to have a brightness_hw_changed attribute then the LED_BRIGHT_HW_CHANGED
flag must be set in flags before registering. Calling
led_classdev_notify_brightness_hw_changed on a classdev not registered with
the LED_BRIGHT_HW_CHANGED flag is a bug and will trigger a WARN_ON.
Hardware accelerated blink of LEDs
==================================