The ACPI information is stored in the /sys/firmware/acpi/tables virtual filesystem that is created by the kernel at boot by accessing onboard ROM. The easy way to read the ACPI tables is with the acpidump command from the acpica-tools package.
ACPI has both methods and data, unlike the device-tree, which is more of a hardware-description language. ACPI methods continue to be active post-boot.
For example, starting the command acpi_listen (from package apcid) and opening and closing the laptop lid will show that ACPI functionality is running all the time.
Updating ACPI tables
While temporarily and dynamically overwriting the ACPI tables is possible, permanently changing them involves interacting with the BIOS menu at boot or reflashing the ROM.
Coreboot
Coreboot is an open-source firmware alternative to traditional BIOS or UEFI, designed for speed, security, and transparency. Unlike standard firmware, Coreboot can load ACPI tables from the OS or filesystem, allowing ACPI updates without reflashing the firmware. This flexibility makes it popular in privacy-focused devices like Chromebooks and Purism laptops, as well as in embedded and server environments.
Coreboot needs to be installed directly onto the computer’s ROM chip (firmware chip) in place of the existing BIOS or UEFI firmware. This installation process, known as flashing, rewrites the firmware with Coreboot’s code.