drivers: console: uart_mux: Initial UART muxing support

Create support for muxed UARTs which are attached to a real
UART and which use GSM 07.10 muxing protocol to create virtual
channels that can be run on top of the real UART.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>

include/drivers/console/uart_mux.h

@@ -0,0 +1,117 @@
+/*
+ * Copyright (c) 2020 Intel Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @file
+ * @brief Public APIs for UART MUX drivers
+ */
+
+#ifndef ZEPHYR_INCLUDE_DRIVERS_UART_MUX_H_
+#define ZEPHYR_INCLUDE_DRIVERS_UART_MUX_H_
+
+/**
+ * @brief UART Mux Interface
+ * @defgroup uart_mux_interface UART Mux Interface
+ * @ingroup io_interfaces
+ * @{
+ */
+
+#include <device.h>
+#include <drivers/uart.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct gsm_dlci;
+
+/**
+ * @typedef uart_mux_attach_cb_t
+ *
+ * @brief Define the user callback function which is called when
+ * the UART mux is attached properly.
+ *
+ * @param mux UART mux device
+ * @param dlci_address DLCI id for the virtual muxing channel
+ * @param connected True if DLCI is connected, false otherwise.
+ * @param user_data Arbitrary user data.
+ */
+typedef void (*uart_mux_attach_cb_t)(struct device *mux, int dlci_address,
+				     bool connected, void *user_data);
+
+/** @brief UART mux driver API structure. */
+__subsystem struct uart_mux_driver_api {
+	/**
+	 * The uart_driver_api must be placed in first position in this
+	 * struct so that we are compatible with uart API. Note that currently
+	 * not all of the UART API functions are implemented.
+	 */
+	struct uart_driver_api uart_api;
+
+	/**
+	 * Attach the mux to this UART. The API will call the callback after
+	 * the DLCI is created or not.
+	 */
+	int (*attach)(struct device *mux, struct device *uart,
+		      int dlci_address, uart_mux_attach_cb_t cb,
+		      void *user_data);
+};
+
+/**
+ * @brief Attach physical/real UART to UART muxing device.
+ *
+ * @param mux UART mux device structure.
+ * @param uart Real UART device structure.
+ * @param dlci_address DLCI id for the virtual muxing channel
+ * @param cb Callback is called when the DLCI is ready and connected
+ * @param user_data Caller supplied optional data
+ *
+ * @retval 0 No errors, the attachment was successful
+ * @retval <0 Error
+ */
+static inline int uart_mux_attach(struct device *mux, struct device *uart,
+				  int dlci_address, uart_mux_attach_cb_t cb,
+				  void *user_data)
+{
+	const struct uart_mux_driver_api *api =
+		(const struct uart_mux_driver_api *)mux->driver_api;
+
+	return api->attach(mux, uart, dlci_address, cb, user_data);
+}
+
+/**
+ * @brief Get UART related to a specific DLCI channel
+ *
+ * @param dlci_address DLCI address, value >0 and <63
+ *
+ * @return UART device if found, NULL otherwise
+ */
+__syscall struct device *uart_mux_find(int dlci_address);
+
+/**
+ * @brief Allocate muxing UART device.
+ *
+ * @details This will return next available uart mux driver that will mux the
+ * data when read or written. This device corresponds to one DLCI channel.
+ * User must first call this to allocate the DLCI and then call the attach
+ * function to fully enable the muxing.
+ *
+ * @retval device New UART device that will automatically mux data sent to it.
+ * @retval NULL if error
+ */
+struct device *uart_mux_alloc(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+#include <syscalls/uart_mux.h>
+
+/**
+ * @}
+ */
+
+#endif /* ZEPHYR_INCLUDE_DRIVERS_UART_MUX_H_ */

include/linker/common-ram.ld

@@ -165,6 +165,16 @@
 		__net_l2_data_end = .;
 	} GROUP_DATA_LINK_IN(RAMABLE_REGION, ROMABLE_REGION)
 
+#if defined(CONFIG_UART_MUX)
+	SECTION_DATA_PROLOGUE(uart_mux,,SUBALIGN(4))
+	{
+		__uart_mux_start = .;
+		*(".uart_mux.*")
+		KEEP(*(SORT_BY_NAME(".uart_mux.*")))
+		__uart_mux_end = .;
+	} GROUP_DATA_LINK_IN(RAMABLE_REGION, ROMABLE_REGION)
+#endif
+
 #if defined(CONFIG_USB_DEVICE_STACK)
 	SECTION_DATA_PROLOGUE(usb_descriptor,,SUBALIGN(1))
 	{