drivers: serial: nrfx_uarte: Fix low power mode for interrupt driven API

Low power mode for non-asynchronous API case is only available when
RX is not used (RX pin is not defined). In that case TX starting
function was using uarte_enable_locked() which tracks if UARTE is
used by TX or RX and TXSTOPPED interrupt was disabling UARTE
unconditionally. Because of that following attempt to TX start
was assuming that UARTE is already enabled when it was disabled.
Fixing it by using uarte_disable_locked function in TXSTOPPED
handling.

Code reordering was required to make uarte_disable_locked()
available earlier.

Signed-off-by: Krzysztof Chruściński <[email protected]>

Author: nordic-krch

drivers/serial/uart_nrfx_uarte.c

@@ -340,6 +340,13 @@ struct uarte_nrfx_config {
 	uint8_t *poll_in_byte;
 };
 
+/* Using Macro instead of static inline function to handle NO_OPTIMIZATIONS case
+ * where static inline fails on linking.
+ */
+#define HW_RX_COUNTING_ENABLED(config)    \
+	(IS_ENABLED(UARTE_ANY_HW_ASYNC) ? \
+	 (config->flags & UARTE_CFG_FLAG_HW_BYTE_COUNTING) : false)
+
 static inline NRF_UARTE_Type *get_uarte_instance(const struct device *dev)
 {
 	const struct uarte_nrfx_config *config = dev->config;
@@ -362,6 +369,44 @@ static void endtx_isr(const struct device *dev)
 
 }
 
+/** @brief Disable UARTE peripheral is not used by RX or TX.
+ *
+ * It must be called with interrupts locked so that deciding if no direction is
+ * using the UARTE is atomically performed with UARTE peripheral disabling. Otherwise
+ * it would be possible that after clearing flags we get preempted and UARTE is
+ * enabled from the higher priority context and when we come back UARTE is disabled
+ * here.
+ * @param dev Device.
+ * @param dis_mask Mask of direction (RX or TX) which now longer uses the UARTE instance.
+ */
+static void uarte_disable_locked(const struct device *dev, uint32_t dis_mask)
+{
+	struct uarte_nrfx_data *data = dev->data;
+
+	data->flags &= ~dis_mask;
+	if (data->flags & UARTE_FLAG_LOW_POWER) {
+		return;
+	}
+
+#if defined(UARTE_ANY_ASYNC) && !defined(CONFIG_UART_NRFX_UARTE_ENHANCED_RX)
+	const struct uarte_nrfx_config *config = dev->config;
+
+	if (data->async && HW_RX_COUNTING_ENABLED(config)) {
+		nrfx_timer_disable(&config->timer);
+		/* Timer/counter value is reset when disabled. */
+		data->async->rx.total_byte_cnt = 0;
+		data->async->rx.total_user_byte_cnt = 0;
+	}
+#endif
+
+#ifdef CONFIG_SOC_NRF54H20_GPD
+	const struct uarte_nrfx_config *cfg = dev->config;
+
+	nrf_gpd_retain_pins_set(cfg->pcfg, true);
+#endif
+	nrf_uarte_disable(get_uarte_instance(dev));
+}
+
 #ifdef UARTE_ANY_NONE_ASYNC
 /**
  * @brief Interrupt service routine.
@@ -397,7 +442,7 @@ static void uarte_nrfx_isr_int(const void *arg)
 				pm_device_runtime_put_async(dev, K_NO_WAIT);
 			}
 		} else {
-			nrf_uarte_disable(uarte);
+			uarte_disable_locked(dev, UARTE_FLAG_LOW_POWER_TX);
 		}
 #ifdef UARTE_INTERRUPT_DRIVEN
 		if (!data->int_driven)
@@ -617,13 +662,6 @@ static int wait_tx_ready(const struct device *dev)
 	return key;
 }
 
-/* Using Macro instead of static inline function to handle NO_OPTIMIZATIONS case
- * where static inline fails on linking.
- */
-#define HW_RX_COUNTING_ENABLED(config)    \
-	(IS_ENABLED(UARTE_ANY_HW_ASYNC) ? \
-	 (config->flags & UARTE_CFG_FLAG_HW_BYTE_COUNTING) : false)
-
 static void uarte_periph_enable(const struct device *dev)
 {
 	NRF_UARTE_Type *uarte = get_uarte_instance(dev);
@@ -726,44 +764,6 @@ static void tx_start(const struct device *dev, const uint8_t *buf, size_t len)
 }
 
 #if defined(UARTE_ANY_ASYNC)
-/** @brief Disable UARTE peripheral is not used by RX or TX.
- *
- * It must be called with interrupts locked so that deciding if no direction is
- * using the UARTE is atomically performed with UARTE peripheral disabling. Otherwise
- * it would be possible that after clearing flags we get preempted and UARTE is
- * enabled from the higher priority context and when we come back UARTE is disabled
- * here.
- * @param dev Device.
- * @param dis_mask Mask of direction (RX or TX) which now longer uses the UARTE instance.
- */
-static void uarte_disable_locked(const struct device *dev, uint32_t dis_mask)
-{
-	struct uarte_nrfx_data *data = dev->data;
-
-	data->flags &= ~dis_mask;
-	if (data->flags & UARTE_FLAG_LOW_POWER) {
-		return;
-	}
-
-#if !defined(CONFIG_UART_NRFX_UARTE_ENHANCED_RX)
-	const struct uarte_nrfx_config *config = dev->config;
-
-	if (data->async && HW_RX_COUNTING_ENABLED(config)) {
-		nrfx_timer_disable(&config->timer);
-		/* Timer/counter value is reset when disabled. */
-		data->async->rx.total_byte_cnt = 0;
-		data->async->rx.total_user_byte_cnt = 0;
-	}
-#endif
-
-#ifdef CONFIG_SOC_NRF54H20_GPD
-	const struct uarte_nrfx_config *cfg = dev->config;
-
-	nrf_gpd_retain_pins_set(cfg->pcfg, true);
-#endif
-	nrf_uarte_disable(get_uarte_instance(dev));
-}
-
 static void rx_timeout(struct k_timer *timer);
 static void tx_timeout(struct k_timer *timer);