Issues with custom board files & simple peripherals.

Question

I'm bringing up a custom board, working through the peripherals one at a time. Unfortunately, I haven't gotten very far before things started misbehaving. One part of the design will be an RGB status LED, with PWM for colour & intensity. Here's a snippet which should work as far as I can see. I'm able to drive the individual LEDs fine, but the PWM will not work at all. Note - LEDs are active low, if relevant.

Source Code

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#if PWM_TEST == 1
        #define PWM_PERIOD_NS   20000000
        #define PWM_PULSE_NS    10000000
        #define PWM_GREEN       DT_ALIAS(pwmgreen)
        static const struct pwm_dt_spec pwm_green = PWM_DT_SPEC_GET(PWM_GREEN);
#endif

int main() {
#if PWM_TEST == 1
  if (!pwm_is_ready_dt(&pwm_green)) {
                LOG_ERR("Error: PWM device %s is not ready\n", pwm_green.dev->name);
                return 0;
        }

        int err = pwm_set_dt(&pwm_green, PWM_PERIOD_NS, PWM_PULSE_NS);
        if (err) {
                LOG_ERR("Error in pwm_set_dt(), err: %d", err);
                return 0;
        }
#endif
}

DTS

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leds {
        compatible = "gpio-leds"; // generic compatible

        ledred: led_red {
            gpios = <&gpio0 0 GPIO_ACTIVE_LOW>;
            label = "Red LED";
        };

        ledgreen: led_green {
            gpios = <&gpio0 2 GPIO_ACTIVE_LOW>;
            label = "Green LED";
        };

        ledblue: led_blue {
            gpios = <&gpio0 1 GPIO_ACTIVE_LOW>;
            label = "Blue LED";
        };

        vccswen: vcc_sw_en {
            gpios = <&gpio0 31 GPIO_ACTIVE_LOW>;
            label = "VCC Switch Enable";
        };
    };

    pwmleds {
        compatible = "pwm-leds";

        pwm_led0: pwm_led_0 {
            pwms = <&pwm0 0 PWM_MSEC(20) PWM_POLARITY_NORMAL>;
        };

        pwm_led1: pwm_led_1 {
            pwms = <&pwm0 1 PWM_MSEC(20) PWM_POLARITY_NORMAL>;
        };

        pwm_led2: pwm_led_2 {
            pwms = <&pwm0 2 PWM_MSEC(20) PWM_POLARITY_NORMAL>;
        };
    };

aliases {

        ledred = &ledred;
        ledgreen = &ledgreen;
        ledblue = &ledblue;
        vccswen = &vccswen;
        pwmled0 = &pwm_led0;
        pwmred = &pwm_led0;
        pwmgreen = &pwm_led2;
        pwmblue = &pwm_led1;
        mode = &button_mode;

        watchdog0 = &wdt0;
    };

proj.conf

------------

...

CONFIG_PWM=y

CONFIG_PWM_LOG_LEVEL_DBG=y

CONFIG_LED=y

CONFIG_LED_PWM=y