Add PM Runtime and Policy Lock support for MSPM0 UART

dts/arm/ti/mspm0/g/mspm0g.dtsi

@@ -231,6 +231,7 @@
 			current-speed = <115200>;
 			clocks = <&ckm MSPM0_CLOCK_ULPCLK>;
 			clk-div = <1>;
+			zephyr,disabling-power-states = <&stdby1>;
 			status = "disabled";
 		};
 
@@ -241,6 +242,7 @@
 			current-speed = <115200>;
 			clocks = <&ckm MSPM0_CLOCK_ULPCLK>;
 			clk-div = <1>;
+			zephyr,disabling-power-states = <&stdby1>;
 			status = "disabled";
 		};
 
@@ -251,6 +253,7 @@
 			current-speed = <115200>;
 			clocks = <&ckm MSPM0_CLOCK_ULPCLK>;
 			clk-div = <1>;
+			zephyr,disabling-power-states = <&stdby1>;
 			status = "disabled";
 		};
 

dts/arm/ti/mspm0/g/mspm0g110x.dtsi

@@ -1,3 +1,11 @@
-/* SPDX-License-Identifier: Apache-2.0 */
+/*
+ * SPDX-FileCopyrightText: 2026 Texas Instruments Incorporated
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
 
 #include <ti/mspm0/g/mspm0g.dtsi>
+
+&uart3 {
+	zephyr,disabling-power-states = <&stop0 &stop1 &stop2 &stdby0 &stdby1>;
+};

dts/arm/ti/mspm0/g/mspm0g150x.dtsi

@@ -6,6 +6,10 @@
 
 #include <ti/mspm0/g/mspm0g.dtsi>
 
+&uart3 {
+	zephyr,disabling-power-states = <&stop0 &stop1 &stop2 &stdby0 &stdby1>;
+};
+
 / {
 	soc {
 		dac0: dac@40018000 {

dts/arm/ti/mspm0/g/mspm0g310x.dtsi

@@ -1,7 +1,15 @@
-/* SPDX-License-Identifier: Apache-2.0 */
+/*
+ * SPDX-FileCopyrightText: 2026 Texas Instruments Incorporated
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
 
 #include <ti/mspm0/g/mspm0g.dtsi>
 
+&uart3 {
+	zephyr,disabling-power-states = <&stop0 &stop1 &stop2 &stdby0 &stdby1>;
+};
+
 / {
 	soc {
 		aes: aes@40442000 {

dts/arm/ti/mspm0/g/mspm0gx51x.dtsi

@@ -229,3 +229,7 @@
 		 <&gpio_none>,
 		 <&gpio_none>;
 };
+
+&uart3 {
+	zephyr,disabling-power-states = <&stop0 &stop1 &stop2 &stdby0 &stdby1>;
+};

dts/arm/ti/mspm0/l/mspm0l110x.dtsi

@@ -59,6 +59,7 @@
 			current-speed = <115200>;
 			clocks = <&ckm MSPM0_CLOCK_ULPCLK>;
 			clk-div = <1>;
+			zephyr,disabling-power-states = <&stdby1>;
 			status = "disabled";
 		};
 	};

dts/arm/ti/mspm0/l/mspm0lx22x.dtsi

@@ -173,6 +173,7 @@
 			current-speed = <9600>;
 			clocks = <&ckm MSPM0_CLOCK_ULPCLK>;
 			clk-div = <1>;
+			zephyr,disabling-power-states = <&stdby1>;
 			status = "disabled";
 		};
 
@@ -183,6 +184,7 @@
 			current-speed = <9600>;
 			clocks = <&ckm MSPM0_CLOCK_ULPCLK>;
 			clk-div = <1>;
+			zephyr,disabling-power-states = <&stdby1>;
 			status = "disabled";
 		};
 
@@ -193,6 +195,7 @@
 			current-speed = <9600>;
 			clocks = <&ckm MSPM0_CLOCK_ULPCLK>;
 			clk-div = <1>;
+			zephyr,disabling-power-states = <&stdby1>;
 			status = "disabled";
 		};
 
@@ -203,6 +206,7 @@
 			current-speed = <9600>;
 			clocks = <&ckm MSPM0_CLOCK_ULPCLK>;
 			clk-div = <1>;
+			zephyr,disabling-power-states = <&stdby1>;
 			status = "disabled";
 		};
 

dts/arm/ti/mspm0/mspm0.dtsi

@@ -264,6 +264,7 @@
 			current-speed = <115200>;
 			clocks = <&ckm MSPM0_CLOCK_ULPCLK>;
 			clk-div = <1>;
+			zephyr,disabling-power-states = <&stdby1>;
 			status = "disabled";
 		};
 

subsys/pm/device_runtime.c

@@ -21,6 +21,13 @@ LOG_MODULE_DECLARE(pm_device, CONFIG_PM_DEVICE_LOG_LEVEL);
 #define PM_DOMAIN(_pm) NULL
 #endif
 
+/*
+ * Serializes all pm->base.usage updates for devices without the ISR-safe
+ * flag. The get/put fast paths read and update the usage counter under this
+ * lock, possibly from interrupt context, so the slow paths must not modify
+ * it under the per-device semaphore alone.
+ */
+static struct k_spinlock lock;
 #ifdef CONFIG_PM_DEVICE_RUNTIME_ASYNC
 #ifdef CONFIG_PM_DEVICE_RUNTIME_USE_DEDICATED_WQ
 K_THREAD_STACK_DEFINE(pm_device_runtime_stack, CONFIG_PM_DEVICE_RUNTIME_DEDICATED_WQ_STACK_SIZE);
@@ -33,6 +40,82 @@ static struct k_work_q pm_device_runtime_wq;
 
 #define EVENT_MASK		(EVENT_STATE_ACTIVE | EVENT_STATE_SUSPENDED)
 
+/* Increment the usage counter of a device under the global lock. */
+static void runtime_usecount_inc(struct pm_device *pm)
+{
+	__ASSERT_NO_MSG(pm != NULL);
+
+	K_SPINLOCK(&lock) {
+		pm->base.usage++;
+	}
+}
+
+/* Decrement the usage counter of a device under the global lock. */
+static void runtime_usecount_dec(struct pm_device *pm)
+{
+	__ASSERT_NO_MSG(pm != NULL);
+
+	K_SPINLOCK(&lock) {
+		pm->base.usage--;
+	}
+}
+
+/*
+ * Release one usage reference under the global lock, unless this is the
+ * last reference. Last-user handling needs the per-device semaphore and
+ * is left to the caller.
+ *
+ * @retval true If the reference was released.
+ * @retval false If this is the last reference.
+ */
+static bool runtime_usage_put_fast(struct pm_device *pm)
+{
+	bool released = false;
+
+	__ASSERT_NO_MSG(pm != NULL);
+
+	K_SPINLOCK(&lock) {
+		if (pm->base.usage > 1U) {
+			pm->base.usage--;
+			released = true;
+		}
+	}
+
+	return released;
+}
+
+/*
+ * Release one usage reference under the global lock, with the per-device
+ * semaphore held by the caller.
+ *
+ * @retval 1 If this was the last reference and the device has to be
+ * suspended.
+ * @retval 0 If other references remain and nothing else has to be done.
+ * @retval -EALREADY If the usage counter was already zero.
+ */
+static int runtime_usage_put(struct pm_device *pm)
+{
+	int ret;
+
+	__ASSERT_NO_MSG(pm != NULL);
+	/* Caller must hold the per-device semaphore, except in pre-kernel
+	 * mode where it is never taken (single-threaded boot).
+	 */
+	__ASSERT(k_is_pre_kernel() || (k_sem_count_get(&pm->lock) == 0),
+		 "pm lock not owned");
+
+	K_SPINLOCK(&lock) {
+		if (pm->base.usage == 0U) {
+			ret = -EALREADY;
+		} else {
+			pm->base.usage--;
+			ret = (pm->base.usage == 0U) ? 1 : 0;
+		}
+	}
+
+	return ret;
+}
+
 /**
  * @brief Suspend a device
  *
@@ -65,6 +148,11 @@ static int runtime_suspend(const struct device *dev, bool async,
 		return 0;
 	}
 
+	/* If we are not the last user, return. */
+	if (runtime_usage_put_fast(pm)) {
+		return 0;
+	}
+
 	if (k_is_pre_kernel()) {
 		async = false;
 	} else {
@@ -74,16 +162,14 @@ static int runtime_suspend(const struct device *dev, bool async,
 		}
 	}
 
-	if (pm->base.usage == 0U) {
-		LOG_WRN("Unbalanced suspend");
-		ret = -EALREADY;
-		goto unlock;
-	}
-
-	pm->base.usage--;
-	if (pm->base.usage > 0U) {
+	ret = runtime_usage_put(pm);
+	if (ret <= 0) {
+		if (ret < 0) {
+			LOG_WRN("Unbalanced suspend");
+		}
 		goto unlock;
 	}
+	ret = 0;
 
 	if (async) {
 		/* queue suspend */
@@ -99,7 +185,7 @@ static int runtime_suspend(const struct device *dev, bool async,
 		/* suspend now */
 		ret = pm->base.action_cb(pm->dev, PM_DEVICE_ACTION_SUSPEND);
 		if (ret < 0) {
-			pm->base.usage++;
+			runtime_usecount_inc(pm);
 			goto unlock;
 		}
 
@@ -131,7 +217,7 @@ static void runtime_suspend_work(struct k_work *work)
 
 	(void)k_sem_take(&pm->lock, K_FOREVER);
 	if (ret < 0) {
-		pm->base.usage++;
+		runtime_usecount_inc(pm);
 		pm->base.state = PM_DEVICE_STATE_ACTIVE;
 	} else {
 		pm->base.state = PM_DEVICE_STATE_SUSPENDED;
@@ -219,6 +305,21 @@ int pm_device_runtime_get(const struct device *dev)
 	}
 
 	if (!k_is_pre_kernel()) {
+		bool early_exit = false;
+
+		K_SPINLOCK(&lock) {
+			/* If we are not the first user and device is active, return. */
+			if ((pm->base.usage > 0U) && (pm->base.state == PM_DEVICE_STATE_ACTIVE)) {
+				pm->base.usage++;
+				early_exit = true;
+			}
+		}
+
+		if (early_exit == true) {
+			ret = 0;
+			goto end;
+		}
+
 		ret = k_sem_take(&pm->lock, k_is_in_isr() ? K_NO_WAIT : K_FOREVER);
 		if (ret < 0) {
 			return -EWOULDBLOCK;
@@ -251,7 +352,7 @@ int pm_device_runtime_get(const struct device *dev)
 		atomic_set_bit(&pm->base.flags, PM_DEVICE_FLAG_PD_CLAIMED);
 	}
 
-	pm->base.usage++;
+	runtime_usecount_inc(pm);
 
 #ifdef CONFIG_PM_DEVICE_RUNTIME_ASYNC
 	/*
@@ -287,7 +388,7 @@ int pm_device_runtime_get(const struct device *dev)
 
 	ret = pm->base.action_cb(pm->dev, PM_DEVICE_ACTION_RESUME);
 	if (ret < 0) {
-		pm->base.usage--;
+		runtime_usecount_dec(pm);
 		if (domain != NULL) {
 			(void)pm_device_runtime_put(domain);
 			atomic_clear_bit(&dev->pm_base->flags, PM_DEVICE_FLAG_PD_CLAIMED);

tests/drivers/uart/uart_elementary/boards/lp_mspm0g3519.conf

@@ -0,0 +1,2 @@
+CONFIG_PM_DEVICE=y
+CONFIG_PM_DEVICE_RUNTIME=y

tests/drivers/uart/uart_elementary/boards/lp_mspm0g3519.overlay

@@ -10,4 +10,5 @@ dut: &uart1 {
 	current-speed = <115200>;
 	hw-flow-control;
 	status = "okay";
+	zephyr,pm-device-runtime-auto;
 };

tests/drivers/uart/uart_elementary/boards/lp_mspm0l2228.conf

@@ -0,0 +1,2 @@
+CONFIG_PM_DEVICE=y
+CONFIG_PM_DEVICE_RUNTIME=y

tests/drivers/uart/uart_elementary/boards/lp_mspm0l2228.overlay

@@ -20,6 +20,7 @@
 			pinctrl-names = "default";
 			hw-flow-control;
 			status = "okay";
+			zephyr,pm-device-runtime-auto;
 		};
 	};
 };

tests/drivers/uart/uart_mix_fifo_poll/boards/lp_mspm0g3519.conf

@@ -1,4 +1,6 @@
 CONFIG_STRESS_TEST_REPS=1000
+CONFIG_PM_DEVICE=y
+CONFIG_PM_DEVICE_RUNTIME=y
 # On Cortex-M0+ _IRQ_PRIO_OFFSET is 0, so SysTick shares the highest NVIC
 # priority with all peripherals. The k_timer expiry (uart_poll_out() spinning
 # on a full TX FIFO) then starves the counter ISR that drains the 4-deep RX

tests/drivers/uart/uart_mix_fifo_poll/boards/lp_mspm0g3519.overlay

@@ -14,6 +14,7 @@ dut: &uart1 {
 	current-speed = <9600>;
 	rx-fifo-threshold = <MSPM0_UART_RX_FIFO_LEVEL_ONE_ENTRY>;
 	status = "okay";
+	zephyr,pm-device-runtime-auto;
 };
 
 counter_dev: &counterg6 {

tests/drivers/uart/uart_mix_fifo_poll/boards/lp_mspm0l2228.conf

@@ -1,4 +1,6 @@
 CONFIG_STRESS_TEST_REPS=1000
+CONFIG_PM_DEVICE=y
+CONFIG_PM_DEVICE_RUNTIME=y
 # On Cortex-M0+ _IRQ_PRIO_OFFSET is 0, so SysTick shares the highest NVIC
 # priority with all peripherals. The k_timer expiry (uart_poll_out() spinning
 # on a full TX FIFO) then starves the counter ISR that drains the 4-deep RX

tests/drivers/uart/uart_mix_fifo_poll/boards/lp_mspm0l2228.overlay

@@ -13,6 +13,7 @@ dut: &uart1 {
 	pinctrl-0 = <&uart1_tx_pb4 &uart1_rx_pb5>;
 	pinctrl-names = "default";
 	status = "okay";
+	zephyr,pm-device-runtime-auto;
 };
 
 &timg8 {

tests/drivers/uart/uart_pm/boards/lp_mspm0g3519.overlay

@@ -0,0 +1,21 @@
+/*
+ * Copyright (c) 2026 Texas Instruments Incorporated
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/dt-bindings/uart/mspm0_uart.h>
+
+/* TX (PB4) and RX (PB5) must be connected together for loopback */
+/*zephyr,pm-device-runtime-auto;*/
+dut: &uart1 {
+	pinctrl-0 = <&uart1_tx_pb4 &uart1_rx_pb5>;
+	pinctrl-names = "default";
+	current-speed = <9600>;
+	rx-fifo-threshold = <MSPM0_UART_RX_FIFO_LEVEL_ONE_ENTRY>;
+	status = "okay";
+};
+
+&cpu0 {
+	cpu-power-states = <&run0 &run1 &run2>;
+};