drivers: serial: Implement serial wrapper to add DTR

This driver wraps an existing UART device and adds
DTR (Data Terminal Ready) GPIO output for a runtime
power management.
When the UART is powered off, DTR is deasserted.
When the UART is powered on, DTR is asserted.

This allows remote end to shut down the UART when DTR is deasserted.

Signed-off-by: Seppo Takalo <[email protected]>

Author: SeppoTakalo

drivers/serial/CMakeLists.txt

@@ -32,6 +32,7 @@ zephyr_library_sources_ifdef(CONFIG_UART_CC23X0 uart_cc23x0.c)
 zephyr_library_sources_ifdef(CONFIG_UART_CC32XX uart_cc32xx.c)
 zephyr_library_sources_ifdef(CONFIG_UART_CDNS uart_cdns.c)
 zephyr_library_sources_ifdef(CONFIG_UART_CMSDK_APB uart_cmsdk_apb.c)
+zephyr_library_sources_ifdef(CONFIG_UART_DTR uart_dtr.c)
 zephyr_library_sources_ifdef(CONFIG_UART_EFINIX_SAPPIHIRE uart_efinix_sapphire.c)
 zephyr_library_sources_ifdef(CONFIG_UART_EMUL uart_emul.c)
 zephyr_library_sources_ifdef(CONFIG_UART_ENE_KB106X uart_ene_kb106x.c)

drivers/serial/Kconfig

@@ -173,6 +173,7 @@ rsource "Kconfig.cc23x0"
 rsource "Kconfig.cc32xx"
 rsource "Kconfig.cdns"
 rsource "Kconfig.cmsdk_apb"
+rsource "Kconfig.dtr"
 rsource "Kconfig.efinix_sapphire"
 rsource "Kconfig.emul"
 rsource "Kconfig.ene"

drivers/serial/Kconfig.dtr

@@ -0,0 +1,26 @@
+# DTR wrapper UART configuration options
+
+# Copyright (c) 2025 Nordic Semiconductor ASA
+# SPDX-License-Identifier: Apache-2.0
+
+config UART_DTR
+	bool "UART DTR wrapper driver"
+	default y
+	depends on DT_HAS_ZEPHYR_UART_DTR_ENABLED
+	depends on GPIO
+	depends on PM_DEVICE_RUNTIME
+	help
+	  Enable UART DTR wrapper driver. This driver wraps an existing UART
+	  device and adds DTR (Data Terminal Ready) functionality for runtime
+	  power management. When UART is powered, the DTR signal is asserted,
+	  and when the UART is powered down, the DTR signal is de-asserted.
+	  The driver acts as a child node of the actual UART.
+
+config UART_DTR_INIT_PRIORITY
+	int "UART DTR driver init priority"
+	default 60
+	depends on UART_DTR
+	help
+	  UART DTR wrapper driver initialization priority. This should be
+	  higher than the underlying UART driver but lower than devices
+	  that depend on it. Generally set higher than CONFIG_UART_INIT_PRIORITY.