sj201-rev10-pwm-fan-overlay-pi5.dts

/*
 * Device Tree Overlay for SJ-201 Rev6&10 - XMOS VocalFusion 3510-INT PWM fan.
 * 
 * This overlay configures a PWM (Pulse Width Modulation) controlled fan connected
 * to the SJ201 Rev6&10 board. It sets up the necessary GPIO pin for PWM output,
 * configures the PWM channel, and defines thermal management properties to
 * control the fan speed based on the CPU temperature.
 *
 * The fan is controlled based on predefined temperature thresholds (trips),
 * adjusting its speed to maintain optimal thermal conditions.
 *
 * Instructions:
 * Compile this DTO with the following command:
 * dtc -@ -H epapr -O dtb -o sj201-rev10-pwm-fan-overlay-pi5.dtbo -Wno-unit_address_vs_reg sj201-rev10-pwm-fan-overlay-pi5.dts
 */

/dts-v1/;
/plugin/;

/ {
    compatible = "brcm,bcm2835";

    /* Configure the GPIO pin for PWM output */
    fragment@0 {
        target = <&rp1_gpio>;
        __overlay__ {
            pwm_pins: pwm_pins {
                brcm,pins = <13>;         // GPIO pin 13 for PWM output
                brcm,function = <4>;      // Set pin function to ALT0 for PWM
                brcm,pull = <0>;          // Disable internal pull-up/down resistors
            };
        };
    };

    /* Configure the PWM channel */
    fragment@1 {
        target = <&rp1_gpio>;
        __overlay__ {
            pinctrl-names = "default";
            pinctrl-0 = <&pwm_pins>;              // Use the configured GPIO pin
            assigned-clock-rates = <2400000>;     // Set PWM clock rate
            status = "okay";
        };
    };

    /* Define the PWM fan device */
    fragment@2 {
        target-path = "/";
        __overlay__ {
            fan0: sj201-rev10-pwm-fan@0 {
                compatible = "pwm-fan";
                cooling-min-state = <0>;            // Minimum fan speed state
                cooling-max-state = <4>;            // Maximum fan speed state
                #cooling-cells = <2>;               // Cooling cells for fan speed control
                cooling-levels = <255 192 129 66 0>; // Define cooling levels (inverted polarity)
                pwms = <&pwm 1 1000000 0>;          // Configure PWM: channel, period (1s), flags
                status = "okay";
            };
        };
    };

    /* Configure thermal management properties */
    fragment@3 {
        target = <&cpu_thermal>;
        __overlay__ {
            trips {
                // Define temperature thresholds and hysteresis for activating cooling states
                trip0: trip0 { temperature = <40000>; hysteresis = <10000>; type = "active"; };
                trip1: trip1 { temperature = <50000>; hysteresis = <2000>;  type = "active"; };
                trip2: trip2 { temperature = <55000>; hysteresis = <2000>;  type = "active"; };
                trip3: trip3 { temperature = <60000>; hysteresis = <4000>;  type = "active"; };
            };
            cooling-maps {
                // Map temperature thresholds (trips) to specific fan speed states
                map0 { trip = <&trip0>; cooling-device = <&fan0 0 1>; };
                map1 { trip = <&trip1>; cooling-device = <&fan0 1 2>; };
                map2 { trip = <&trip2>; cooling-device = <&fan0 2 3>; };
                map3 { trip = <&trip3>; cooling-device = <&fan0 3 4>; };
            };
        };
    };

    /* Overrides for setting temperatures and hysteresis via kernel command line */
    __overrides__ {
        poe_fan_temp0 = <&trip0>,"temperature:0";
        poe_fan_temp0_hyst = <&trip0>,"hysteresis:0";
        poe_fan_temp1 = <&trip1>,"temperature:0";
        poe_fan_temp1_hyst = <&trip1>,"hysteresis:0";
        poe_fan_temp2 = <&trip2>,"temperature:0";
        poe_fan_temp2_hyst = <&trip2>,"hysteresis:0";
        poe_fan_temp3 = <&trip3>,"temperature:0";
        poe_fan_temp3_hyst = <&trip3>,"hysteresis:0";
    };
};