LED: inform userspace about brightness change

From: Pali RohÃr
Date: Wed Dec 24 2014 - 15:06:29 EST


What is preferred way from kernel driver to inform userspace
about LED device brightness change? In /sys/class/leds/<device>/
is file brightness which can be used to read current brightness
or set write new value. But sometimes also firmware (or device)
can change value on its own and thus userspace software which
provides slider for setting brightness will be incorrect.

For example on Dell laptops there is driver which support setting
and reading keyboard backlight (via leds kernel interface). But
firmware/BIOS can change brightness (when something happen) and
it can inform running system about this change via ACPI/WMI event
interface. But how to use kernel led interface to inform userpace
about this change? It is possible?

Pali RohÃr

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