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97f6c81103
Under-voltage due to inadequate power supplies is a recurring problem for new Raspberry Pi users. There are visual indications that an under-voltage situation is occuring like blinking power led and a lightning icon on the desktop (not shown when using the vc4 driver), but for new users it's not obvious that this signifies a critical situation. This patch provides a twofold improvement to the situation: Firstly it logs under-voltage events to the kernel log. This provides information also for headless installations. Secondly it provides a sysfs file to read the value. This improves on 'vcgencmd' by providing change notification. Userspace can poll on the file and be notified of changes to the value. A script can poll the file and use dbus notification to put a windows on the desktop with information about the severity with a recommendation to change the power supply. A link to more information can also be provided. Only changes to the sticky bits are reported (cleared between readings). Signed-off-by: Noralf Trønnes <noralf@tronnes.org>