drivers: add SC16IS75x series UART controllers driver

This driver manages the UART controller part of an SC16IS75x MFD,
for a specific UART channel. Using the interrupt driven UART API
required interrupt handling on the parent MFD, which may require
an additional work queue thread to perform non-blocking bus
transfers.

Signed-off-by: Sarah Renkhoff <sarah.renkhoff@navimatix.de>
Signed-off-by: Stephan Linz <linz@li-pro.net>

drivers/CMakeLists.txt

@@ -8,3 +8,4 @@ add_subdirectory_ifdef(CONFIG_I2C i2c)
 add_subdirectory_ifdef(CONFIG_MFD mfd)
 add_subdirectory_ifdef(CONFIG_RTC rtc)
 add_subdirectory_ifdef(CONFIG_SENSOR sensor)
+add_subdirectory_ifdef(CONFIG_SERIAL serial)

drivers/Kconfig

@@ -10,5 +10,6 @@ rsource "i2c/Kconfig"
 rsource "mfd/Kconfig"
 rsource "rtc/Kconfig"
 rsource "sensor/Kconfig"
+rsource "serial/Kconfig"
 
 endmenu

drivers/serial/CMakeLists.txt

@@ -0,0 +1,6 @@
+# Copyright (c) 2024 TiaC Systems
+# SPDX-License-Identifier: Apache-2.0
+
+zephyr_library_amend()
+
+zephyr_library_sources_ifdef(CONFIG_UART_SC16IS75X	uart_sc16is75x.c)

drivers/serial/Kconfig

@@ -0,0 +1,8 @@
+# Copyright (c) 2024 TiaC Systems
+# SPDX-License-Identifier: Apache-2.0
+
+if SERIAL
+
+rsource "Kconfig.sc16is75x"
+
+endif # SERIAL

drivers/serial/Kconfig.sc16is75x

@@ -0,0 +1,36 @@
+# Copyright (c) 2024 TiaC Systems
+# SPDX-License-Identifier: Apache-2.0
+
+menuconfig UART_SC16IS75X
+	bool "NXP SC16IS75x UART driver"
+	default y
+	depends on DT_HAS_NXP_SC16IS75X_UART_ENABLED
+	depends on MFD_SC16IS75X
+	help
+	  Enable driver for UART controller part of an SC16IS75x bridge.
+
+if UART_SC16IS75X
+
+config UART_SC16IS75X_LOOPBACK
+	bool "Enable internal loopback"
+	help
+	  Enable the NXP SC16IS75x local UART loopback mode (internal).
+
+	  In this mode the RTS and DTR signals are looped back to the
+	  CTS and DSR and the TX output is looped back to the RX input
+	  internally for all channels.
+
+config UART_SC16IS75X_INIT_PRIORITY
+	int "Init priority"
+	default 60
+	help
+	  Device driver initialization priority.
+
+config UART_SC16IS75X_INTERRUPT_DRIVEN
+	bool
+	default y if UART_INTERRUPT_DRIVEN
+	default n
+	depends on MFD_SC16IS75X_INTERRUPTS
+	depends on MFD_SC16IS75X_ASYNC
+
+endif # UART_SC16IS75X