Acpi and Drivers — How the System Talks About Itself
A short explainer of the Advanced Configuration and Power Interface — what it describes and how drivers use it.
What Acpi Provides
Acpi is a description provided by firmware for the operating system to read at boot. It lists the devices on the platform that are not auto-discoverable, the power states each one supports, and the methods to switch between states.
Without Acpi, the operating system would have to guess about platform-specific devices like the embedded controller, the lid switch, or the power button. With it, drivers know exactly what is there and how to control it.
How Drivers Use Acpi Methods
Drivers call Acpi methods to put their devices into low-power states, to wake them, to read sensors, and to handle hot-plug events. The methods are described in firmware tables and executed by an interpreter inside the operating system.
When the operating system tells a device to suspend, it is often executing an Acpi method on the driver's behalf. The result is consistent power management across very different hardware platforms.
When Acpi Tables Are the Issue
Buggy Acpi tables in firmware can cause devices to misbehave on suspend, wake at unexpected times, or report wrong sensor values. Bios updates from the system maker are the right way to address these — operating system patches sometimes work around them but cannot rewrite them.
For Linux users, the dmesg output at boot lists Acpi-related warnings. Persistent ones often correlate with known issues that the system maker has acknowledged on their support page.
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