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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>
57 lines
2.3 KiB
ReStructuredText
57 lines
2.3 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0-or-later
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Kernel driver arctic_fan_controller
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=====================================
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Supported devices:
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* ARCTIC Fan Controller (USB HID, VID 0x3904, PID 0xF001)
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Author: Aureo Serrano de Souza <aureo.serrano@arctic.de>
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Description
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-----------
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This driver provides hwmon support for the ARCTIC Fan Controller, a USB
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Custom HID device with 10 fan channels. The device sends IN reports about
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once per second containing current RPM values (bytes 11-30, 10 x uint16 LE).
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Fan speed control is manual-only: the device does not change PWM
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autonomously; it only applies a new duty cycle when it receives an OUT
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report from the host.
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After the device applies an OUT report, it sends back a 2-byte ACK IN
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report (Report ID 0x02, byte 1 = 0x00 on success) confirming the command
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was applied.
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Usage notes
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-----------
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Since it is a USB device, hotplug is supported. The device is autodetected.
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The device does not support GET_REPORT, so the driver cannot read back the
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current hardware PWM state at probe time. The cached PWM values (readable
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via pwm[1-10]) start at 0 and reflect only values that have been
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successfully written. Because each OUT report carries all 10 channel values,
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writing a single channel also sends the cached values for all other channels.
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Users should set all channels to the desired values before relying on the
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cached state.
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On system suspend, the device may lose power and reset its PWM channels to
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hardware defaults. The driver clears its cached duty values on resume so
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that reads reflect the unknown hardware state rather than stale pre-suspend
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values. Userspace is responsible for re-applying the desired duty cycles
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after resume.
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Sysfs entries
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-------------
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================ ==============================================================
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fan[1-10]_input Fan speed in RPM (read-only). Updated from IN reports at ~1 Hz.
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pwm[1-10] PWM duty cycle (0-255). Write: sends an OUT report setting the
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duty cycle (scaled from 0-255 to 0-100% for the device);
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the cached value is updated only after the device ACKs the
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command with a success status. Read: returns the last
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successfully written value; initialized to 0 at driver load
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and after resume (hardware state unknown).
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================ ==============================================================
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