modem: modem_cellular: revert baudrate on reset

Revert the UART port baudrate to its original value after performing a
pin reset on the modem.

Signed-off-by: Jordan Yates <[email protected]>

Author: JordanYates

drivers/modem/modem_cellular.c

@@ -107,6 +107,7 @@ struct modem_cellular_data {
 	struct modem_backend_uart uart_backend;
 	uint8_t uart_backend_receive_buf[CONFIG_MODEM_CELLULAR_UART_BUFFER_SIZES];
 	uint8_t uart_backend_transmit_buf[CONFIG_MODEM_CELLULAR_UART_BUFFER_SIZES];
+	uint32_t original_baudrate;
 
 	/* CMUX */
 	struct modem_cmux cmux;
@@ -829,6 +830,30 @@ static int modem_cellular_on_idle_state_leave(struct modem_cellular_data *data)
 	return 0;
 }
 
+static uint32_t modem_cellular_baudrate_update(struct modem_cellular_data *data,
+						uint32_t desired_baudrate)
+{
+	const struct modem_cellular_config *config =
+		(const struct modem_cellular_config *)data->dev->config;
+	struct uart_config cfg = {0};
+	uint32_t original_baudrate;
+	int ret;
+
+	ret = uart_config_get(config->uart, &cfg);
+	if (ret < 0) {
+		LOG_ERR("Failed to get UART configuration (%d)", ret);
+		return 0;
+	}
+	original_baudrate = cfg.baudrate;
+	cfg.baudrate = desired_baudrate;
+	ret = uart_configure(config->uart, &cfg);
+	if (ret < 0) {
+		LOG_ERR("Failed to set new baudrate (%d)", ret);
+		return 0;
+	}
+	return original_baudrate;
+}
+
 static int modem_cellular_on_reset_pulse_state_enter(struct modem_cellular_data *data)
 {
 	const struct modem_cellular_config *config =
@@ -838,6 +863,11 @@ static int modem_cellular_on_reset_pulse_state_enter(struct modem_cellular_data
 		gpio_pin_set_dt(&config->wake_gpio, 0);
 	}
 
+	/* Revert to original baudrate if we have changed it */
+	if (data->original_baudrate) {
+		modem_cellular_baudrate_update(data, data->original_baudrate);
+	}
+
 	gpio_pin_set_dt(&config->reset_gpio, 1);
 	modem_cellular_start_timer(data, K_MSEC(config->reset_pulse_duration_ms));
 	return 0;
@@ -961,8 +991,6 @@ static void modem_cellular_set_baudrate_event_handler(struct modem_cellular_data
 {
 	const struct modem_cellular_config *config =
 		(const struct modem_cellular_config *)data->dev->config;
-	struct uart_config cfg = {0};
-	int ret;
 
 	switch (evt) {
 	case MODEM_CELLULAR_EVENT_BUS_OPENED:
@@ -986,17 +1014,9 @@ static void modem_cellular_set_baudrate_event_handler(struct modem_cellular_data
 		modem_pipe_attach(data->uart_pipe, modem_cellular_bus_pipe_handler, data);
 		modem_pipe_close_async(data->uart_pipe);
 
-		ret = uart_config_get(config->uart, &cfg);
-		if (ret < 0) {
-			LOG_ERR("Failed to get UART configuration (%d)", ret);
-			break;
-		}
-		cfg.baudrate = CONFIG_MODEM_CELLULAR_NEW_BAUDRATE;
-		ret = uart_configure(config->uart, &cfg);
-		if (ret < 0) {
-			LOG_ERR("Failed to set new baudrate (%d)", ret);
-			break;
-		}
+		/* Update UART port baudrate and preserve the original value */
+		data->original_baudrate = modem_cellular_baudrate_update(
+			data, CONFIG_MODEM_CELLULAR_NEW_BAUDRATE);
 		break;
 
 	case MODEM_CELLULAR_EVENT_BUS_CLOSED: