drivers: pwm_mcux_sctimer: Add PM support for low power modes

Enables sleep mode (PM3) in RW61x. Once any channel is configured,
PWM driver blocks standby and suspend modes idefinitely since there
is no API to disable PWM outputs.

Signed-off-by: Alex Rodriguez <[email protected]>

Author: alrodlim

drivers/pwm/Kconfig.mcux_sctimer

@@ -1,4 +1,4 @@
-# Copyright 2021 NXP
+# Copyright 2021, 2025 NXP
 # SPDX-License-Identifier: Apache-2.0
 
 config PWM_MCUX_SCTIMER
@@ -9,3 +9,12 @@ config PWM_MCUX_SCTIMER
 	select PINCTRL
 	help
 	  Enable sctimer based pwm driver.
+
+config PWM_MCUX_SCT_KEEP_STATE
+	bool "Retain output level after PWM is disabled"
+	default y
+	help
+	  When enabled, the PWM driver will hold the inactive output level and
+	  retain the power management lock even after the PWM signal is
+	  stopped (pulse = 0). This prevents the pin from floating or losing state
+	  in low power modes where the peripheral or pad may be disabled.

drivers/pwm/pwm_mcux_sctimer.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, NXP
+ * Copyright 2021, 2025 NXP
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -16,6 +16,9 @@
 
 #include <zephyr/logging/log.h>
 
+#include <zephyr/pm/policy.h>
+#include <zephyr/pm/device.h>
+
 LOG_MODULE_REGISTER(pwm_mcux_sctimer, CONFIG_PWM_LOG_LEVEL);
 
 #define CHANNEL_COUNT FSL_FEATURE_SCT_NUMBER_OF_OUTPUTS
@@ -36,6 +39,11 @@ struct pwm_mcux_sctimer_data {
 	sctimer_pwm_signal_param_t channel[CHANNEL_COUNT];
 	uint32_t match_period;
 	uint32_t configured_chan;
+	/* This flag keeps track of active/idle channels
+	 * to determine whether to allow low power mode
+	 * or not (see PWM_MCUX_SCTIMER_RETAIN_INACTIVE_STATE).
+	 */
+	uint32_t active_chan;
 };
 
 /* Helper to setup channel that has not previously been configured for PWM */
@@ -75,9 +83,50 @@ static int mcux_sctimer_new_channel(const struct device *dev,
 
 	SCTIMER_StartTimer(config->base, kSCTIMER_Counter_U);
 	data->configured_chan++;
+	data->active_chan++;
+
 	return 0;
 }
 
+static void mcux_sctimer_pwm_update_channel(const struct device *dev, uint32_t channel,
+					    uint8_t duty_cycle)
+{
+	const struct pwm_mcux_sctimer_config *config = dev->config;
+	struct pwm_mcux_sctimer_data *data = dev->data;
+	SCT_Type *base = config->base;
+
+	SCTIMER_UpdatePwmDutycycle(base, channel, duty_cycle,
+				   data->event_number[channel]);
+
+	if (duty_cycle > 0 && data->channel[channel].dutyCyclePercent == 0) {
+		data->active_chan++;
+	}
+
+	if (duty_cycle == 0 && data->channel[channel].dutyCyclePercent > 0) {
+		data->active_chan--;
+	}
+
+	data->channel[channel].dutyCyclePercent = duty_cycle;
+
+	if (data->active_chan == 0) {
+		/* No channels active. Stop the sctimer to manually set the output.
+		 * Set the output to inactive state. Output for other channels
+		 * already at the correct level. Just need to update the current one.
+		 */
+		SCTIMER_StopTimer(base, kSCTIMER_Counter_U);
+
+		if (data->channel[channel].level == kSCTIMER_HighTrue) {
+			base->OUTPUT &= ~(1UL << channel);
+		} else {
+			base->OUTPUT |= (1UL << channel);
+		}
+
+#ifndef CONFIG_PWM_MCUX_SCT_KEEP_STATE
+		pm_policy_device_power_lock_put(dev);
+#endif
+	}
+}
+
 static int mcux_sctimer_pwm_set_cycles(const struct device *dev,
 				       uint32_t channel, uint32_t period_cycles,
 				       uint32_t pulse_cycles, pwm_flags_t flags)
@@ -106,21 +155,10 @@ static int mcux_sctimer_pwm_set_cycles(const struct device *dev,
 	duty_cycle = 100 * pulse_cycles / period_cycles;
 
 	if (duty_cycle == 0 && data->configured_chan == 1) {
-		/* Only one channel is active. We can turn off the SCTimer
+		/* Only one channel is configured. We can turn off the SCTimer
 		 * global counter.
 		 */
-		SCT_Type *base = config->base;
-
-		/* Stop timer so we can set output directly */
-		SCTIMER_StopTimer(base, kSCTIMER_Counter_U);
-
-		/* Set the output to inactive State */
-		if (data->channel[channel].level == kSCTIMER_HighTrue) {
-			base->OUTPUT &= ~(1UL << channel);
-		} else {
-			base->OUTPUT |= (1UL << channel);
-		}
-
+		mcux_sctimer_pwm_update_channel(dev, channel, duty_cycle);
 		return 0;
 	}
 
@@ -147,6 +185,10 @@ static int mcux_sctimer_pwm_set_cycles(const struct device *dev,
 		if (ret < 0) {
 			return ret;
 		}
+
+		/* Block from losing power while PWM output is enabled. */
+		pm_policy_device_power_lock_get(dev);
+
 	} else if (data->event_number[channel] == EVENT_NOT_SET) {
 		/* We have already configured a PWM signal, but this channel
 		 * has not been setup. We can only support this channel
@@ -168,7 +210,7 @@ static int mcux_sctimer_pwm_set_cycles(const struct device *dev,
 		 */
 		if (data->configured_chan != 1) {
 			LOG_ERR("Cannot change PWM period when multiple "
-				"channels active");
+				"channels configured");
 			return -ENOTSUP;
 		}
 
@@ -183,8 +225,7 @@ static int mcux_sctimer_pwm_set_cycles(const struct device *dev,
 		data->match_period = period_cycles;
 	} else {
 		/* Only duty cycle needs to be updated */
-		SCTIMER_UpdatePwmDutycycle(config->base, channel, duty_cycle,
-					   data->event_number[channel]);
+		mcux_sctimer_pwm_update_channel(dev, channel, duty_cycle);
 	}
 
 	return 0;
@@ -207,7 +248,7 @@ static int mcux_sctimer_pwm_get_cycles_per_sec(const struct device *dev,
 	return 0;
 }
 
-static int mcux_sctimer_pwm_init(const struct device *dev)
+static int mcux_sctimer_pwm_init_common(const struct device *dev)
 {
 	const struct pwm_mcux_sctimer_config *config = dev->config;
 	struct pwm_mcux_sctimer_data *data = dev->data;
@@ -239,10 +280,51 @@ static int mcux_sctimer_pwm_init(const struct device *dev)
 	}
 	data->match_period = 0;
 	data->configured_chan = 0;
+	data->active_chan = 0;
 
 	return 0;
 }
 
+/* Note: This driver does not save and restore state when entering or exiting
+ * low power mode due to limitations in the SDK drivers. Users should ensure
+ * that the required configuration is reapplied after waking up from low power
+ * states.
+ */
+static int mcux_sctimer_pwm_driver_pm_action(const struct device *dev,
+					     enum pm_device_action action)
+{
+	const struct pwm_mcux_sctimer_config *config = dev->config;
+	int err = 0;
+
+	switch (action) {
+	case PM_DEVICE_ACTION_RESUME:
+		break;
+	case PM_DEVICE_ACTION_TURN_ON:
+		err = mcux_sctimer_pwm_init_common(dev);
+		break;
+	case PM_DEVICE_ACTION_SUSPEND:
+		break;
+	case PM_DEVICE_ACTION_TURN_OFF:
+		/* Reaching this point implies that all the PWM channels
+		 * are in idle state and the SCTimer counter is disabled.
+		 */
+		err = pinctrl_apply_state(config->pincfg, PINCTRL_STATE_SLEEP);
+		break;
+	default:
+		err = -ENOTSUP;
+	}
+
+	return err;
+}
+
+static int mcux_sctimer_pwm_init(const struct device *dev)
+{
+	/* The device init is done from the PM_DEVICE_ACTION_TURN_ON in
+	 * the pm callback which is invoked by pm_device_driver_init.
+	 */
+	return pm_device_driver_init(dev, mcux_sctimer_pwm_driver_pm_action);
+}
+
 static DEVICE_API(pwm, pwm_mcux_sctimer_driver_api) = {
 	.set_cycles = mcux_sctimer_pwm_set_cycles,
 	.get_cycles_per_sec = mcux_sctimer_pwm_get_cycles_per_sec,
@@ -259,10 +341,10 @@ static DEVICE_API(pwm, pwm_mcux_sctimer_driver_api) = {
 		.clock_dev = DEVICE_DT_GET(DT_INST_CLOCKS_CTLR(n)),		\
 		.clock_subsys = (clock_control_subsys_t)DT_INST_CLOCKS_CELL(n, name),\
 	};										\
-											\
+	PM_DEVICE_DT_INST_DEFINE(n, mcux_sctimer_pwm_driver_pm_action);			\
 	DEVICE_DT_INST_DEFINE(n,							\
 			      mcux_sctimer_pwm_init,					\
-			      NULL,							\
+			      PM_DEVICE_DT_INST_GET(n),					\
 			      &pwm_mcux_sctimer_data_##n,				\
 			      &pwm_mcux_sctimer_config_##n,				\
 			      POST_KERNEL, CONFIG_PWM_INIT_PRIORITY,			\