linux

hwmon: add driver for ARCTIC Fan Controller Add hwmon driver for the ARCTIC Fan Controller, a USB HID device (VID 0x3904, PID 0xF001) with 10 fan channels. Exposes fan speed in RPM (read-only) and PWM duty cycle (0-255, read/write) via sysfs. The device pushes IN reports at ~1 Hz containing RPM readings. PWM is set via OUT reports; the device applies the new duty cycle and sends back a 2-byte ACK (Report ID 0x02). The driver waits up to 1 s for the ACK using a completion. Measured device latency: max ~563 ms over 500 iterations. PWM control is manual-only: the device never changes duty cycle autonomously. raw_event() may run in hardirq context, so fan_rpm[] is protected by a spinlock with irq-save. pwm_duty[] is also protected by this spinlock because reset_resume() clears it outside the hwmon core lock. The OUT report buffer is built and write_pending is armed under the same lock so that no reset_resume() can race with the pwm_duty[] snapshot. priv->buf is exclusively accessed by write(), which the hwmon core serializes. Signed-off-by: Aureo Serrano de Souza <aureo.serrano@arctic.de> Link: https://lore.kernel.org/r/20260508064405.38676-1-aureo.serrano@arctic.de Signed-off-by: Guenter Roeck <linux@roeck-us.net> 2026-05-08 14:44:00 +08:00