Re: [PATCH v7 RESEND] hwmon: add driver for ARCTIC Fan Controller

[Guenter Roeck <linux@roeck-us.net>]

On Fri, May 08, 2026 at 02:44:00PM +0800, Aureo Serrano de Souza wrote:
> 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>

I guess we can live with the potential 1-second sysfs read stall on driver
unload reported by Sashiko. Applied.

Thanks,
Guenter