Module thermal 

ACPI thermal management : temperature reading and fan control.

On Lenovo ThinkPads (X13, T14, etc.), the Embedded Controller (EC) exposes temperature sensors and fan control registers at known offsets. This driver reads the CPU temperature and controls the fan via the EC.

ThinkPad EC register map (verified for X13 Gen 1/2)

Register	Description
0x78	CPU temperature (°C, unsigned)
0x79	GPU temperature (°C, unsigned)
0x7A	Battery temperature (°C)
0x93	Fan control: bit 0 = enable,
	bits 1–7 = speed level (0=max)
0x94	Fan speed (RPM, 16-bit LE)
0x84	EC query: thermal event

Structs

ThermalState

Thermal state snapshot, read atomically from EC registers.

Enums

FanSpeed

Fan speed levels for the ThinkPad manual fan control. Level 0 = maximum speed, 7 = off. The EC uses an inverted scale.

Constants

EC_REG_FAN_CTRL 🔒

EC register: fan control byte.

EC_REG_FAN_SPEED 🔒

EC register: fan speed in RPM (16-bit little-endian).

EC_REG_TEMP_BAT 🔒

EC register: battery temperature in degrees Celsius.

EC_REG_TEMP_CPU 🔒

EC register: CPU temperature in degrees Celsius.

EC_REG_TEMP_GPU 🔒

EC register: GPU temperature in degrees Celsius.

FAN_MAX_THRESHOLD 🔒

FAN_OFF_THRESHOLD 🔒

FAN_ON_THRESHOLD 🔒

Temperature thresholds for fan control (in °C).

Statics

AUTO_FAN_CONTROL 🔒

Whether automatic fan control is enabled.

LAST_CPU_TEMP 🔒

Last read CPU temperature (for quick non-locking access).

LAST_FAN_RPM 🔒

Last read fan RPM (for quick non-locking access).

THERMAL_INITIALIZED 🔒

Whether thermal management is initialized.

THERMAL_STATE 🔒

Latest thermal snapshot (updated by periodic polling).

Functions

auto_fan_control 🔒

Automatic fan control logic based on CPU temperature.

cpu_temperature

Get the last known CPU temperature (lock-free).

dump_status

Dump thermal status to serial console.

fan_rpm

Get the last known fan RPM (lock-free).

init

Initialize the thermal subsystem.

poll

Update the cached thermal state. Call periodically (e.g., from timer tick).

read_thermal_state

Read the current thermal state from EC registers.

set_auto_fan_control

Enable automatic fan control based on CPU temperature.

set_fan_enabled

Enable or disable the fan entirely.

set_fan_speed

Set the fan to a specific speed level.