From dbcbd87d3313d6a08f7bd70edf1f6a5058416870 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Krzysztof=20Chru=C5=9Bci=C5=84ski?=
 <krzysztof.chruscinski@nordicsemi.no>
Date: Tue, 17 Sep 2024 14:15:04 +0200
Subject: [PATCH] [nrf fromlist] drivers: serial: nrfx_uarte: Add workaround
 for BAUDRATE register
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On uart120 BAUDRATE register is not retained when ENABLE=0 and
because of that BAUDRATE must be set after enabling. Add workaround
to the driver.

Upstream PR: https://github.com/zephyrproject-rtos/zephyr/pull/75462

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>
---
 drivers/serial/uart_nrfx_uarte.c | 39 ++++++++++++++++++++++++++++++--
 1 file changed, 37 insertions(+), 2 deletions(-)

diff --git a/drivers/serial/uart_nrfx_uarte.c b/drivers/serial/uart_nrfx_uarte.c
index 5da9c6b2702..150bd83725b 100644
--- a/drivers/serial/uart_nrfx_uarte.c
+++ b/drivers/serial/uart_nrfx_uarte.c
@@ -103,6 +103,16 @@ LOG_MODULE_REGISTER(uart_nrfx_uarte, 0);
 #define UARTE_ANY_CACHE 1
 #endif
 
+#ifdef UARTE_ANY_CACHE
+/* uart120 instance does not retain BAUDRATE register when ENABLE=0. When this instance
+ * is used then baudrate must be set after enabling the peripheral and not before.
+ * This approach works for all instances so can be generally applied when uart120 is used.
+ * It is not default for all because it costs some resources. Since currently only uart120
+ * needs cache, that is used to determine if workaround shall be applied.
+ */
+#define UARTE_BAUDRATE_RETENTION_WORKAROUND 1
+#endif
+
 /*
  * RX timeout is divided into time slabs, this define tells how many divisions
  * should be made. More divisions - higher timeout accuracy and processor usage.
@@ -187,6 +197,9 @@ struct uarte_nrfx_int_driven {
 struct uarte_nrfx_data {
 #ifdef CONFIG_UART_USE_RUNTIME_CONFIGURE
 	struct uart_config uart_config;
+#ifdef UARTE_BAUDRATE_RETENTION_WORKAROUND
+	nrf_uarte_baudrate_t nrf_baudrate;
+#endif
 #endif
 #ifdef UARTE_INTERRUPT_DRIVEN
 	struct uarte_nrfx_int_driven *int_driven;
@@ -387,7 +400,6 @@ static int baudrate_set(const struct device *dev, uint32_t baudrate)
 	const struct uarte_nrfx_config *config = dev->config;
 	/* calculated baudrate divisor */
 	nrf_uarte_baudrate_t nrf_baudrate = NRF_BAUDRATE(baudrate);
-	NRF_UARTE_Type *uarte = get_uarte_instance(dev);
 
 	if (nrf_baudrate == 0) {
 		return -EINVAL;
@@ -398,7 +410,15 @@ static int baudrate_set(const struct device *dev, uint32_t baudrate)
 		nrf_baudrate /= config->clock_freq / NRF_UARTE_BASE_FREQUENCY_16MHZ;
 	}
 
+#ifdef UARTE_BAUDRATE_RETENTION_WORKAROUND
+	struct uarte_nrfx_data *data = dev->data;
+
+	data->nrf_baudrate = nrf_baudrate;
+#else
+	NRF_UARTE_Type *uarte = get_uarte_instance(dev);
+
 	nrf_uarte_baudrate_set(uarte, nrf_baudrate);
+#endif
 
 	return 0;
 }
@@ -582,6 +602,13 @@ static void uarte_enable(const struct device *dev, uint32_t act_mask, uint32_t s
 	}
 #endif
 	nrf_uarte_enable(get_uarte_instance(dev));
+#if UARTE_BAUDRATE_RETENTION_WORKAROUND
+	nrf_uarte_baudrate_t baudrate = COND_CODE_1(CONFIG_UART_USE_RUNTIME_CONFIGURE,
+			(data->nrf_baudrate),
+			(((const struct uarte_nrfx_config *)dev->config)->nrf_baudrate));
+
+	nrf_uarte_baudrate_set(get_uarte_instance(dev), baudrate);
+#endif
 }
 
 /* At this point we should have irq locked and any previous transfer completed.
@@ -2140,12 +2167,19 @@ static int uarte_nrfx_pm_action(const struct device *dev,
 
 	switch (action) {
 	case PM_DEVICE_ACTION_RESUME:
-		ret = pinctrl_apply_state(cfg->pcfg, PINCTRL_STATE_DEFAULT);
+	{
+		ret = pins_state_change(dev, true);
 		if (ret < 0) {
 			return ret;
 		}
 
 		nrf_uarte_enable(uarte);
+#if UARTE_BAUDRATE_RETENTION_WORKAROUND
+		nrf_uarte_baudrate_t baudrate = COND_CODE_1(CONFIG_UART_USE_RUNTIME_CONFIGURE,
+			(data->nrf_baudrate), (cfg->nrf_baudrate));
+
+		nrf_uarte_baudrate_set(get_uarte_instance(dev), baudrate);
+#endif
 
 #ifdef UARTE_ANY_ASYNC
 		if (data->async) {
@@ -2169,6 +2203,7 @@ static int uarte_nrfx_pm_action(const struct device *dev,
 #endif
 		}
 		break;
+	}
 	case PM_DEVICE_ACTION_SUSPEND:
 		/* Disabling UART requires stopping RX, but stop RX event is
 		 * only sent after each RX if async UART API is used.