drivers: serial: nrfx_uarte: Support for low power polling mode

Add support for getting to the lowest power mode when polling is
used with disable-rx property and interrupts are not used for
that UARTE. So far disabling of the UARTE peripheral was done in
the interrupt but in some cases interrupt may not be available
and in that case uart_poll_out shall wait until byte is transferred
and put UARTE into the lowest power state.

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

Author: nordic-krch

drivers/serial/Kconfig.nrfx

@@ -28,6 +28,14 @@ config UART_NRFX_UARTE
 	imply NRFX_UARTE_CONFIG_SKIP_PSEL_CONFIG if !UART_NRFX_UARTE_LEGACY_SHIM
 	imply NRFX_UARTE_CONFIG_SKIP_GPIO_CONFIG if !UART_NRFX_UARTE_LEGACY_SHIM
 
+config UART_NRFX_UARTE_NO_IRQ
+	bool "Polling without interrupt"
+	depends on UART_NRFX_UARTE
+	depends on !UART_ASYNC_API && !UART_INTERRUPT_DRIVEN
+	help
+	  When enabled, then interrupt handler is not used at all and it is possible
+	  to get to the lowest power state after uart_poll_out if receiver is not used.
+
 config UART_NRFX_UARTE_LEGACY_SHIM
 	bool "Legacy UARTE shim"
 	depends on UART_NRFX_UARTE

drivers/serial/uart_nrfx_uarte.c

@@ -373,6 +373,8 @@ static inline NRF_UARTE_Type *get_uarte_instance(const struct device *dev)
 	return config->uarte_regs;
 }
 
+#if !defined(CONFIG_UART_NRFX_UARTE_NO_IRQ)
+
 static void endtx_isr(const struct device *dev)
 {
 	NRF_UARTE_Type *uarte = get_uarte_instance(dev);
@@ -388,6 +390,8 @@ static void endtx_isr(const struct device *dev)
 
 }
 
+#endif
+
 /** @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
@@ -426,7 +430,7 @@ static void uarte_disable_locked(const struct device *dev, uint32_t dis_mask)
 	nrf_uarte_disable(get_uarte_instance(dev));
 }
 
-#ifdef UARTE_ANY_NONE_ASYNC
+#if defined(UARTE_ANY_NONE_ASYNC) && !defined(CONFIG_UART_NRFX_UARTE_NO_IRQ)
 /**
  * @brief Interrupt service routine.
  *
@@ -503,7 +507,7 @@ static void uarte_nrfx_isr_int(const void *arg)
 	}
 #endif /* UARTE_INTERRUPT_DRIVEN */
 }
-#endif /* UARTE_ANY_NONE_ASYNC */
+#endif /* UARTE_ANY_NONE_ASYNC && !CONFIG_UART_NRFX_UARTE_NO_IRQ */
 
 #ifdef CONFIG_UART_USE_RUNTIME_CONFIGURE
 /**
@@ -1978,14 +1982,36 @@ static void uarte_nrfx_poll_out(const struct device *dev, unsigned char c)
 		}
 	}
 
-	if (IS_ENABLED(CONFIG_PM_DEVICE_RUNTIME) || LOW_POWER_ENABLED(config)) {
+	if (!IS_ENABLED(CONFIG_UART_NRFX_UARTE_NO_IRQ) &&
+	    (IS_ENABLED(CONFIG_PM_DEVICE_RUNTIME) || LOW_POWER_ENABLED(config))) {
 		nrf_uarte_int_enable(uarte, NRF_UARTE_INT_TXSTOPPED_MASK);
 	}
 
 	*config->poll_out_byte = c;
 	tx_start(dev, config->poll_out_byte, 1);
 
 	irq_unlock(key);
+
+	if (IS_ENABLED(CONFIG_UART_NRFX_UARTE_NO_IRQ)) {
+		key = wait_tx_ready(dev);
+		if (!IS_ENABLED(UARTE_HAS_ENDTX_STOPTX_SHORT) &&
+		    !(config->flags & UARTE_CFG_FLAG_PPI_ENDTX)) {
+			nrf_uarte_task_trigger(uarte, NRF_UARTE_TASK_STOPTX);
+			nrf_uarte_event_clear(uarte, NRF_UARTE_EVENT_TXSTOPPED);
+			while (!nrf_uarte_event_check(uarte, NRF_UARTE_EVENT_TXSTOPPED)) {
+			}
+		}
+
+		if (IS_ENABLED(CONFIG_PM_DEVICE_RUNTIME)) {
+			if (!(data->flags & UARTE_FLAG_POLL_OUT)) {
+				data->flags &= ~UARTE_FLAG_POLL_OUT;
+				pm_device_runtime_put(dev);
+			}
+		} else if (LOW_POWER_ENABLED(config)) {
+			uarte_disable_locked(dev, UARTE_FLAG_LOW_POWER_TX);
+		}
+		irq_unlock(key);
+	}
 }
 
 
@@ -2253,7 +2279,7 @@ static void wait_for_tx_stopped(const struct device *dev)
 	NRFX_WAIT_FOR(nrf_uarte_event_check(uarte, NRF_UARTE_EVENT_TXSTOPPED),
 		      1000, 1, res);
 
-	if (!ppi_endtx) {
+	if (!ppi_endtx && !IS_ENABLED(CONFIG_UART_NRFX_UARTE_NO_IRQ)) {
 		nrf_uarte_int_enable(uarte, NRF_UARTE_INT_ENDTX_MASK);
 	}
 }
@@ -2398,7 +2424,9 @@ static int uarte_tx_path_init(const struct device *dev)
 		}
 		nrf_uarte_event_clear(uarte, NRF_UARTE_EVENT_ENDTX);
 		nrf_uarte_task_trigger(uarte, NRF_UARTE_TASK_STOPTX);
-		nrf_uarte_int_enable(uarte, NRF_UARTE_INT_ENDTX_MASK);
+		if (!IS_ENABLED(CONFIG_UART_NRFX_UARTE_NO_IRQ)) {
+			nrf_uarte_int_enable(uarte, NRF_UARTE_INT_ENDTX_MASK);
+		}
 	}
 	while (!nrf_uarte_event_check(uarte, NRF_UARTE_EVENT_TXSTOPPED)) {
 	}
@@ -2465,9 +2493,10 @@ static int uarte_instance_init(const struct device *dev,
 
 /* Depending on configuration standard or direct IRQ is connected. */
 #define UARTE_IRQ_CONNECT(idx, irqn, prio)							\
-	COND_CODE_1(CONFIG_UART_NRFX_UARTE_DIRECT_ISR,						\
-		(IRQ_DIRECT_CONNECT(irqn, prio, uarte_##idx##_direct_isr, 0)),			\
-		(IRQ_CONNECT(irqn, prio, UARTE_GET_ISR(idx), DEVICE_DT_GET(UARTE(idx)), 0)))
+	COND_CODE_1(CONFIG_UART_NRFX_UARTE_NO_IRQ, (), \
+		(COND_CODE_1(CONFIG_UART_NRFX_UARTE_DIRECT_ISR,					\
+		    (IRQ_DIRECT_CONNECT(irqn, prio, uarte_##idx##_direct_isr, 0)),		\
+		    (IRQ_CONNECT(irqn, prio, UARTE_GET_ISR(idx), DEVICE_DT_GET(UARTE(idx)), 0)))))
 
 #define UARTE_IRQ_CONFIGURE(idx)							   \
 	do {										   \