fwts: battery test should sanity check _BTP via /proc/acpi/battery/*/alarm

[Colin Ian King]

Although many laptops and netbooks don't support _BTP, it is probably worth implementing a _BTP sanity check to test that battery trip points work. The ACPI user space interface exists in /proc/acpi/battery/*/alarm

Conceptually:

Set alarm to a level just below current level, unplug AC adapter, soak CPUs to drain battery, watch for battery event when we drop below the trip point.

See: 10.2.2.7 _BTP (Battery Trip Point) of ACPI specification.

Tests: Does _BTP exist? If so, can we set it? Does it generate an event? Can we cancel it by writing a zero to the /proc interface?

[Colin Ian King (colin-king)]

 Scanned 3336 kernel bugs, 462 contained _BTP, or ~14.8% of ACPI tables in a representative sample have _BTP.

[Colin Ian King (colin-king)]

/sys/bus/acpi/drivers/battery/PNP0C0A:00/power_supply/BAT0/alarm is the new path to this

[Colin Ian King (colin-king)]

Ah, discovered this was already implemented this in the battery test, known as the "trip point" test.

commit ac2eff91db6b464635fc4b95ec32f356370a6562
Author: Alex Hung <email address hidden>
Date: Wed May 23 03:44:32 2012 +0000