Advanced Configuration and Power Interface (ACPI) support for
Linux requires an ACPI-compliant platform (hardware/firmware),
and assumes the presence of OS-directed configuration and power
management (OSPM) software. This option will enlarge your
kernel by about 70K.

Linux ACPI provides a robust functional replacement for several
legacy configuration and power management interfaces, including
the Plug-and-Play BIOS specification (PnP BIOS), the
MultiProcessor Specification (MPS), and the Advanced Power
Management (APM) specification. If both ACPI and APM support
are configured, ACPI is used.

The project home page for the Linux ACPI subsystem is here:
<https://01.org/linux-acpi>

Linux support for ACPI is based on Intel Corporation's ACPI
Component Architecture (ACPI CA). For more information on the
ACPI CA, see:
<http://acpica.org/>

ACPI is an open industry specification originally co-developed by
Hewlett-Packard, Intel, Microsoft, Phoenix, and Toshiba. Currently,
it is developed by the ACPI Specification Working Group (ASWG) under
the UEFI Forum and any UEFI member can join the ASWG and contribute
to the ACPI specification.
The specification is available at:
<http://www.acpi.info>
<http://www.uefi.org/acpi/specs>

source code:

drivers/pci/pci-acpi.c