drivers: serial: Add gpio management to low power mode

When low power mode is enabled then whenever UARTE is not active,
driver attempts to put the peripheral into the lowest power state
by stopping and disabling UARTE. However, it did not put pins into
sleep state which could lead to increased current consumption.
Adding pins state handling to the low power mode.

Pins are put into sleep state only if CONFIG_PM_DEVICE=y.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>

drivers/serial/uart_nrfx_uarte.c

@@ -516,6 +516,20 @@ static int wait_tx_ready(const struct device *dev)
 	return key;
 }
 
+#if defined(UARTE_ANY_ASYNC) || defined(CONFIG_PM_DEVICE)
+static int pins_state_change(const struct device *dev, bool on)
+{
+	const struct uarte_nrfx_config *config = dev->config;
+
+	if (config->flags & UARTE_CFG_FLAG_GPIO_MGMT) {
+		return pinctrl_apply_state(config->pcfg,
+				on ? PINCTRL_STATE_DEFAULT : PINCTRL_STATE_SLEEP);
+	}
+
+	return 0;
+}
+#endif
+
 #ifdef UARTE_ANY_ASYNC
 
 /* Using Macro instead of static inline function to handle NO_OPTIMIZATIONS case
@@ -526,16 +540,22 @@ static int wait_tx_ready(const struct device *dev)
 
 #endif /* UARTE_ANY_ASYNC */
 
-static void uarte_enable(const struct device *dev, uint32_t mask)
+static int uarte_enable(const struct device *dev, uint32_t mask)
 {
 #ifdef UARTE_ANY_ASYNC
 	const struct uarte_nrfx_config *config = dev->config;
 	struct uarte_nrfx_data *data = dev->data;
 
 	if (data->async) {
 		bool disabled = data->async->low_power_mask == 0;
+		int ret;
 
 		data->async->low_power_mask |= mask;
+		ret = pins_state_change(dev, true);
+		if (ret < 0) {
+			return ret;
+		}
+
 		if (HW_RX_COUNTING_ENABLED(data) && disabled) {
 			const nrfx_timer_t *timer = &config->timer;
 
@@ -548,6 +568,8 @@ static void uarte_enable(const struct device *dev, uint32_t mask)
 	}
 #endif
 	nrf_uarte_enable(get_uarte_instance(dev));
+
+	return 0;
 }
 
 /* At this point we should have irq locked and any previous transfer completed.
@@ -571,7 +593,7 @@ static void tx_start(const struct device *dev, const uint8_t *buf, size_t len)
 	nrf_uarte_event_clear(uarte, NRF_UARTE_EVENT_TXSTOPPED);
 
 	if (config->flags & UARTE_CFG_FLAG_LOW_POWER) {
-		uarte_enable(dev, UARTE_LOW_POWER_TX);
+		(void)uarte_enable(dev, UARTE_LOW_POWER_TX);
 		nrf_uarte_int_enable(uarte, NRF_UARTE_INT_TXSTOPPED_MASK);
 	}
 
@@ -853,6 +875,7 @@ static int uarte_nrfx_rx_enable(const struct device *dev, uint8_t *buf,
 	struct uarte_nrfx_data *data = dev->data;
 	const struct uarte_nrfx_config *cfg = dev->config;
 	NRF_UARTE_Type *uarte = get_uarte_instance(dev);
+	int ret = 0;
 
 	if (cfg->disable_rx) {
 		__ASSERT(false, "TX only UARTE instance");
@@ -906,7 +929,7 @@ static int uarte_nrfx_rx_enable(const struct device *dev, uint8_t *buf,
 	if (cfg->flags & UARTE_CFG_FLAG_LOW_POWER) {
 		unsigned int key = irq_lock();
 
-		uarte_enable(dev, UARTE_LOW_POWER_RX);
+		ret = uarte_enable(dev, UARTE_LOW_POWER_RX);
 		irq_unlock(key);
 	}
 
@@ -1279,6 +1302,10 @@ static void async_uart_release(const struct device *dev, uint32_t dir_mask)
 		}
 
 		uart_disable(dev);
+		int err = pins_state_change(dev, false);
+
+		(void)err;
+		__ASSERT_NO_MSG(err == 0);
 	}
 
 	irq_unlock(key);
@@ -1875,14 +1902,21 @@ static int uarte_nrfx_pm_action(const struct device *dev,
 	const struct uarte_nrfx_config *cfg = dev->config;
 	int ret;
 
+#ifdef UARTE_ANY_ASYNC
+	/* If low power mode for asynchronous mode is used then there is nothing to do here.
+	 * In low power mode UARTE is turned off whenever there is no activity.
+	 */
+	if (data->async && (cfg->flags & UARTE_CFG_FLAG_LOW_POWER)) {
+		return 0;
+	}
+#endif
+
 	switch (action) {
 	case PM_DEVICE_ACTION_RESUME:
-		if (cfg->flags & UARTE_CFG_FLAG_GPIO_MGMT) {
-			ret = pinctrl_apply_state(cfg->pcfg,
-						  PINCTRL_STATE_DEFAULT);
-			if (ret < 0) {
-				return ret;
-			}
+
+		ret = pins_state_change(dev, true);
+		if (ret < 0) {
+			return ret;
 		}
 
 		nrf_uarte_enable(uarte);
@@ -1951,12 +1985,9 @@ static int uarte_nrfx_pm_action(const struct device *dev,
 		wait_for_tx_stopped(dev);
 		uart_disable(dev);
 
-		if (cfg->flags & UARTE_CFG_FLAG_GPIO_MGMT) {
-			ret = pinctrl_apply_state(cfg->pcfg,
-						  PINCTRL_STATE_SLEEP);
-			if (ret < 0) {
-				return ret;
-			}
+		ret = pins_state_change(dev, false);
+		if (ret < 0) {
+			return ret;
 		}
 
 		break;