This is a small Linux kernel module for interacting with ACPI-based
ambient light sensors. Unlike the in-tree acpi_als module, als_bus
passes ACPI Notify events 0x80, 0x81, and 0x82 from the
ambient light sensor (generated when the AML determines that a
significant change to illuminance, colour temperature, or response has
occured, respectively) to userspace via the ACPI netlink bus. The
netlink packets’ data field is zero, and their event type field is the
event code received.
It also exposes an als_bus node in the device node in sysfs
(usually found at /sys/bus/acpi/devices/ACPI0008:00/), which
contains the sub-entries ali and alr, for reading the illuminance
and the response table, respectively. The illuminance value is
formatted as a base-10 integer and the response table is formatted
[[a, b], [c, d], ...] with the values in the same order as in
_ALR, specified in section 9.3.5 of the ACPI specification. Note
that at present, the _ALT, _ALC, and _ALP methods are not
exposed in sysfs; if they are exposed in the future, they will be
accessible at alt, alc, and alp under the als_bus node. These
nodes will only be present when the underlying methods exist.