sm_host: DTR/RI implementation for host side

Terms:
Data Terminal Equipment (DTE), AKA. host.
Data Communication Equipment (DCE), AKA. Serial Modem.
Data Terminal Ready (DTR)
Ring Indicate (RI)

DTR operation for DTE:
When DTE wants to enable UART, it resumes UART, enables RX,
asserts DTR and sends any possible pending TX data.

When DTE wants to disable UART, it aborts possible TX,
deasserts DTR, disables RX and suspends UART.

The UART control in DTE can be done either manual or automatic.
With automatic control, UART will be enabled when there is a TX
request and disabled after a configured timeout has passed since
UART was last active.

Replaces following Kconfigs with dtr-gpios & ri-gpios:
CONFIG_SM_HOST_POWER_PIN, CONFIG_SM_HOST_POWER_PIN_TIME and
CONFIG_SM_HOST_INDICATE_PIN.

Signed-off-by: Markus Lassila <markus.lassila@nordicsemi.no>

Author: MarkusLassila

dts/bindings/dte_dtr/nordic,dtr-dte.yaml

@@ -0,0 +1,18 @@
+# Copyright (c) 2025 Nordic Semiconductor ASA
+# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+
+description: |
+    DTE side of DTR/RI UART
+
+compatible: "nordic,dte-dtr"
+
+properties:
+  dtr-gpios:
+    type: phandle-array
+    description: Output. Data Terminal Ready pin
+    required: true
+
+  ri-gpios:
+    type: phandle-array
+    description: Input. Ring Indicator pin
+    required: true

include/sm_host.h

@@ -57,45 +57,62 @@ enum at_cmd_state {
 typedef void (*sm_data_handler_t)(const uint8_t *data, size_t datalen);
 
 /**
- * @typedef sm_ind_handler_t
+ * @typedef sm_ri_handler_t
  *
- * Handler to handle @kconfig{CONFIG_SM_HOST_INDICATE_PIN} signal from Serial Modem.
+ * Handler to handle the Ring Indicate (RI) signal from Serial Modem.
  */
-typedef void (*sm_ind_handler_t)(void);
+typedef void (*sm_ri_handler_t)(void);
 
 /**@brief Initialize Serial Modem Host library.
  *
  * @param handler Pointer to a handler function of type @ref sm_data_handler_t.
+ * @param automatic_uart If true, DTR and UART are automatically managed by the library.
+ * @param inactivity_timeout Inactivity timeout for DTR and UART disablement. Only used if @p
+ * automatic is true.
  *
  * @return Zero on success, non-zero otherwise.
  */
-int sm_host_init(sm_data_handler_t handler);
+int sm_host_init(sm_data_handler_t handler, bool automatic_uart, k_timeout_t inactivity_timeout);
 
 /**@brief Un-initialize Serial Modem Host
  */
 int sm_host_uninit(void);
 
 /**
- * @brief Register callback for @kconfig{CONFIG_SM_HOST_INDICATE_PIN} indication
+ * @brief Register callback for Ring Indicate (RI) pin.
  *
- * @param handler Pointer to a handler function of type @ref sm_ind_handler_t.
- * @param wakeup  Enable/disable System Off wakeup by GPIO Sense.
+ * @param handler Pointer to a handler function of type @ref sm_ri_handler_t.
  *
- * @retval Zero    Success.
- * @retval -EFAULT if @kconfig{CONFIG_SM_HOST_INDICATE_PIN} is not defined.
+ * @retval Zero on success. Otherwise, a (negative) error code is returned.
  */
-int sm_host_register_ind(sm_ind_handler_t handler, bool wakeup);
+int sm_host_register_ri_handler(sm_ri_handler_t handler);
 
 /**
- * @brief Toggle power pin of the nRF91 Series device configured with
- * @kconfig{CONFIG_SM_HOST_POWER_PIN}.
+ * @brief Configure automatic DTR UART handling
  *
- * The pin is enabled for the time specified in @kconfig{CONFIG_SM_HOST_POWER_PIN_TIME}
- * and then disabled.
+ * If automatic DTR UART handling is enabled, the library will enable DTR UART when RI
+ * signal is detected, and disable it after inactivity timeout.
+ *
+ * @param automatic If true, DTR UART is automatically managed by the library.
+ * @param inactivity Inactivity timeout for DTR UART disablement. Only used if @p
+ * automatic is true.
  *
  * @return Zero on success, non-zero otherwise.
  */
-int sm_host_power_pin_toggle(void);
+void sm_host_configure_dtr_uart(bool automatic, k_timeout_t inactivity);
+
+/**
+ * @brief Disable DTR UART
+ *
+ * Disables DTR UART. Disables automatic DTR UART handling.
+ */
+void sm_host_disable_dtr_uart(void);
+
+/** @brief Enable DTR UART
+ *
+ * Enables DTR UART. Disables automatic DTR UART handling.
+ */
+void sm_host_enable_dtr_uart(void);
 
 /**
  * @brief Function to send an AT command in Serial Modem command mode

lib/sm_host/Kconfig

@@ -7,9 +7,11 @@
 menuconfig SM_HOST
 	bool "Serial Modem Host Library"
 	depends on SERIAL
-	depends on UART_ASYNC_API
-	depends on RING_BUFFER
+	select UART_ASYNC_API
+	select RING_BUFFER
 	select UART_USE_RUNTIME_CONFIGURE
+	select GPIO_GET_CONFIG
+	select PM_DEVICE
 
 if SM_HOST
 
@@ -72,26 +74,6 @@ config SM_HOST_CR_LF_TERMINATION
 
 endchoice
 
-config SM_HOST_POWER_PIN
-	int "Power pin"
-	default -1
-	help
-	  Interface GPIO to toggle power pin of the nRF91 Series device.
-
-config SM_HOST_POWER_PIN_TIME
-	int "Power pin active time"
-	default 100
-	help
-	  GPIO active time in milliseconds. This setting specifies
-	  the period length for the pin to be active.
-
-config SM_HOST_INDICATE_PIN
-	int "Indicate pin"
-	default -1
-	help
-	  Interface GPIO pin used by Serial Modem to indicate that data is available or
-	  an unexpected reset has occurred.
-
 module = SM_HOST
 module-str = SM Host
 source "$(ZEPHYR_BASE)/subsys/logging/Kconfig.template.log_config"