Fan Control¶

The Ten64 has a Microchip EMC2301 fan controller which supports fan control over I2C. When a 4-pin fan is installed, you can control the fan speed with PWM.

Ten64 does not support speed control for 3-pin fans.

Ten64 desktop appliances have a Noctua NF-A4x20 PWM installed which has a nominal speed of 5000 RPM.

Fan control in U-Boot¶

Note: The fan control driver and command has not been upstreamed into U-Boot yet. These commands may change into the future.

As the EMC2301 does not have a 'hardware' reset, U-Boot will reset the fan speed to full (target=20000RPM) each boot.

List fan speed

=> fan list
Fan controller: emc2301@2f
 Number of fans: 1
 Fan 0 : 5442 RPM [target 20000]

Enable PWM control for fan

This must be done per-fan, otherwise fan speed commands from U-Boot will not take effect
```
=> fan enable_pwm emc2301@2f 0 1
```

Set fan speed

=> fan set_speed emc2301@2f 0 3000
(wait a few seconds to take effect)
=> fan list
Fan controller: emc2301@2f
 Number of fans: 1
 Fan 0 : 3312 RPM [target 20000]

Fan control in Linux¶

Note

Linux 6.1 and later contains a emc2305 driver. We do not recommend you use this driver at this time, without taking precautions! See the note below.

Traverse driver¶

Fan control in Linux requires the (currently) out of tree emc2301 driver.

This driver is present in our OpenWrt, μVirt and Debian kernel packages.

The device tree in the Ten64 firmware sets the emc2301 as a cooling device for the LS1088, and will step the fan between 3500-5500 RPM. A method to override these settings from U-Boot variables (without having to change the device tree) will be provided in a future firmware release.

The settings will appear in dmesg when the emc2301 module is loaded:

emc2301 0-002f: EMC2301 detected
emc2301 0-002f: Have 1 fans configured in DT
emc2301 0-002f: Fan 0 Cooling step is 312 RPM, minimum 3000, max 5500 RPM
emc2301 0-002f: registering a cooling device

The emc2301 parameters can be controlled from sysfs (see sensors for a more general overview).

As hwmon devices are numbered in the order they are enumerated in, the numbering is not constant between distributions and kernels. One way to identify the hwmon name is to lookup via the I2C platform device:

$ ls /sys/devices/platform/soc/2000000.i2c/i2c-0/0-002f/hwmon/
hwmon3

Read fan speed

$ cat /sys/class/hwmon/hwmon3/fan1_input
4878

Set fan target speed

Note that the thermal subsystem will override the set fan speed if the CPU temperate increases

$ echo 4000 > /sys/class/hwmon/hwmon3/fan1_target
# Wait a few seconds for the fan speed to change
$ cat /sys/class/hwmon/hwmon3/fan1_input
4024

Linux mainline driver (6.1 and later)¶

The Linux mainline emc2305 driver was written by another party and due to limitations around the device tree ecosystem at the time, is missing device tree integration and integration with the Linux thermal subsystem.

As of October 2024, there is no automatic speed control (linked to SoC temperature) available with this driver.

Note

Loading the emc2305 driver will cause the fan to turn off immediately. You must reset the PWM value after loading the driver!

The mainline driver does not implement RPM targets, instead, you must specify the PWM speed as an eight-bit (0-255) value.

# Turn off the fan (do not do this for long periods!):
$ echo 0 > /sys/class/hwmon/hwmon4/pwm1
$ cat /sys/class/hwmon/hwmon4/fan1_input
0

# Turn fan to full speed
$ echo 255 > /sys/class/hwmon/hwmon4/pwm1
$ cat /sys/class/hwmon/hwmon4/fan1_input
5228

# Turn fan to "half" speed (~3000 RPM)
$ echo 128 > /sys/class/hwmon/hwmon4/pwm1
$ cat /sys/class/hwmon/hwmon4/fan1_input
3062