Control fan RPM with multiple thermal zones, advice needed

Banana Pi Router design BPI-R4(MT7988)
1

I’m building a cooling solution for the BPI-R4 that will have a fan moving air through the entire enclosure, and I’d like the fan RPM to follow several thermal zones–the SoC, WiFi PHYs, SFP modules, and the NVMe SSD. I know mt7988a.dtsi is the place to look in. But, it’s an unfamiliar territory for me, so, rather than trying to figure it out on my own, I’d appreciate an advice.

I also suspect that mt7988a-bananapi-bpi-r4.dtsi would be a better place for the new code, as it is device-specific.

This is what I start with in mt7988a.dtsi.

thermal-zones {
		cpu_thermal: cpu-thermal {
			polling-delay-passive = <1000>;
			polling-delay = <1000>;
			thermal-sensors = <&lvts 0>;

			trips {
				cpu_trip_crit: crit {
					temperature = <125000>;
					hysteresis = <2000>;
					type = "critical";
				};

				cpu_trip_hot: hot {
					temperature = <120000>;
					hysteresis = <2000>;
					type = "hot";
				};

				cpu_trip_active_high: active-high {
					temperature = <115000>;
					hysteresis = <2000>;
					type = "active";
				};

				cpu_trip_active_med: active-med {
					temperature = <85000>;
					hysteresis = <2000>;
					type = "active";
				};

				cpu_trip_active_low: active-low {
					temperature = <40000>;
					hysteresis = <2000>;
					type = "active";
				};
			};

			cooling-maps {
				cpu-active-high {
				/* active: set fan to cooling level 2 */
					cooling-device = <&fan 3 3>;
					trip = <&cpu_trip_active_high>;
				};

				cpu-active-low {
				/* active: set fan to cooling level 1 */
					cooling-device = <&fan 2 2>;
					trip = <&cpu_trip_active_med>;
				};

				cpu-passive {
				/* passive: set fan to cooling level 0 */
					cooling-device = <&fan 1 1>;
					trip = <&cpu_trip_active_low>;
				};
			};
		};
	};

I’d also like to connect the fan tachometer to GPIO to be able to read the RPM, but all of the pins on the 26-pin GPIO header seem to have a specific function. What am I missing here?

5899ee2a184ae871929fc76169ed7aab8c58d1585814a952c124f3f3f0a0dd19
5899ee2a184ae871929fc76169ed7aab8c58d1585814a952c124f3f3f0a0dd192604×740 170 KB

2 
	fan: pwm-fan {
		compatible = "pwm-fan";
		/* cooling level (0, 1, 2, 3) : (0% duty, 30% duty, 50% duty, 100% duty) */
		cooling-levels = <0 80 128 255>;
		#cooling-cells = <2>;
		#thermal-sensor-cells = <1>;
		status = "disabled";
	};
3

I figured a better solution would be to use the GPIO header to both power and control the fan with a simple userspace script. It polls every temp sensor found in /sys/class/hwmon and sets the fan speed according to the highest reading. Works fell so far.

#!/bin/sh

# PWM configuration
PWM_PIN="/sys/kernel/debug/pinctrl/1001f000.pinctrl-pinctrl_moore/pinmux-select"
PWM_CHIP="/sys/class/pwm/pwmchip0"
PWM_GROUP="$PWM_CHIP/pwm6"

# Initialize PWM
echo "pwm6_0 pwm" > "$PWM_PIN"
if [ ! -d "$PWM_GROUP" ]; then
        echo 6 > "$PWM_CHIP/export"
fi

# Set frequency to 10 kHz (100000 ns period) and enable PWM
echo 100000 > "$PWM_GROUP/period"
echo 1 > "$PWM_GROUP/enable"

# Set duty cycle
set_duty_cycle() {
	echo "$1" > "$PWM_GROUP/duty_cycle"
}

# Choose duty cicle based on temperature
choose_duty_cycle() {
	temp=$1
	# Full speed if temp >= 60°C
		if [ "$temp" -ge 60000 ]; then
		set_duty_cycle 100000
	# Mid speed if temp >= 45°C
	elif [ "$temp" -ge 45000 ]; then
		set_duty_cycle 50000
	# Low speed if temp < 45°C
	else
		set_duty_cycle 30000
	fi
}

# Loop through all hwmon directories for highest temperature
get_temperature() {
	max_temp=0
	for hwmon in /sys/class/hwmon/hwmon*/temp*_input; do
		if [ -f "$hwmon" ]; then
			temp=$(cat "$hwmon")
			if [ "$temp" -gt "$max_temp" ]; then
				max_temp=$temp
			fi
		fi
	done
	choose_duty_cycle $max_temp
}

# Run continuously
while true; do
	get_temperature
	sleep 5  # Check every 5 seconds
done

Edit: error fixed.

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