Documentation/hwmon/arctic_fan_controller.rst

Source file repositories/reference/linux-study-clean/Documentation/hwmon/arctic_fan_controller.rst

File Facts

System
Linux kernel
Corpus path
Documentation/hwmon/arctic_fan_controller.rst
Extension
.rst
Size
2402 bytes
Lines
57
Domain
Support Tooling And Documentation
Bucket
Documentation
Inferred role
Support Tooling And Documentation: documentation
Status
atlas-only

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

.. SPDX-License-Identifier: GPL-2.0-or-later

Kernel driver arctic_fan_controller
=====================================

Supported devices:

* ARCTIC Fan Controller (USB HID, VID 0x3904, PID 0xF001)

Author: Aureo Serrano de Souza <aureo.serrano@arctic.de>

Description
-----------

This driver provides hwmon support for the ARCTIC Fan Controller, a USB
Custom HID device with 10 fan channels. The device sends IN reports about
once per second containing current RPM values (bytes 11-30, 10 x uint16 LE).
Fan speed control is manual-only: the device does not change PWM
autonomously; it only applies a new duty cycle when it receives an OUT
report from the host.

After the device applies an OUT report, it sends back a 2-byte ACK IN
report (Report ID 0x02, byte 1 = 0x00 on success) confirming the command
was applied.

Usage notes
-----------

Since it is a USB device, hotplug is supported. The device is autodetected.

The device does not support GET_REPORT, so the driver cannot read back the
current hardware PWM state at probe time. The cached PWM values (readable
via pwm[1-10]) start at 0 and reflect only values that have been
successfully written. Because each OUT report carries all 10 channel values,
writing a single channel also sends the cached values for all other channels.
Users should set all channels to the desired values before relying on the
cached state.

On system suspend, the device may lose power and reset its PWM channels to
hardware defaults. The driver clears its cached duty values on resume so
that reads reflect the unknown hardware state rather than stale pre-suspend
values. Userspace is responsible for re-applying the desired duty cycles
after resume.

Sysfs entries
-------------

================ ==============================================================
fan[1-10]_input  Fan speed in RPM (read-only). Updated from IN reports at ~1 Hz.
pwm[1-10]        PWM duty cycle (0-255). Write: sends an OUT report setting the
                 duty cycle (scaled from 0-255 to 0-100% for the device);
                 the cached value is updated only after the device ACKs the
                 command with a success status. Read: returns the last
                 successfully written value; initialized to 0 at driver load
                 and after resume (hardware state unknown).
================ ==============================================================

Annotation

Implementation Notes