drivers: ram_console: add option to link console buffer to given section

Currently, the ram_console buffer is defined as a global var, its
address is determined during the building and may be changed when
code update. This is not a problem if the ram_console is just used
in debug purpose.

While in the heterogeneous SoCs, there can be multiple MPU Cores
and several MCU cores, it can run multiple OS/bare-metal instances
on these cores, but the UART ports may be not enough, so the
ram_console can be leveraged. To make it easy to use, it's better
make the console buffer fixed and predefined.

This patch adds a option to link the console buffer to a given
section, through the "zephyr,memory-region" device tree node, then
the address can be known from the device tree node and easy to
check from other cores running Linux/U-Boot.

To use this option, the chosen property 'zephyr,ram-console' must
be added, the following is a example:

	chosen {
		zephyr,ram-console = &ram_console;
	};

	ram_console: memory@93d00000 {
		compatible = "zephyr,memory-region";
		reg = <0x93d00000 DT_SIZE_K(4)>;
		zephyr,memory-region = "RAM_CONSOLE";
	};

Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>

drivers/console/Kconfig

@@ -95,16 +95,30 @@ config JAILHOUSE_DEBUG_CONSOLE
 	  Useful in board bring-up if there aren't any working serial
 	  drivers.
 
+# Workaround for not being able to have commas in macro arguments
+DT_CHOSEN_Z_RAM_CONSOLE := zephyr,ram-console
+
 config RAM_CONSOLE
 	bool "Use RAM console"
 	select CONSOLE_HAS_DRIVER
+	select RAM_CONSOLE_BUFFER_SECTION if $(dt_chosen_enabled,$(DT_CHOSEN_Z_RAM_CONSOLE))
 	help
 	  Emit console messages to a RAM buffer "ram_console" which can
 	  be examined at runtime with a debugger. Useful in board bring-up
 	  if there aren't any working serial drivers.
 
+config RAM_CONSOLE_BUFFER_SECTION
+	bool "Use dedicated section as RAM console buffer"
+	depends on RAM_CONSOLE && $(dt_chosen_enabled,$(DT_CHOSEN_Z_RAM_CONSOLE))
+	select KERNEL_DIRECT_MAP if MMU
+	help
+	  Use a dedicated section as the RAM console buffer, whose address is
+	  known before build so that the console output messages can be easily
+	  examined by a debugger or software tool from a parallel-running OS.
+
 config RAM_CONSOLE_BUFFER_SIZE
 	int "Ram Console buffer size"
+	default $(dt_chosen_reg_size_int,$(DT_CHOSEN_Z_RAM_CONSOLE)) if RAM_CONSOLE_BUFFER_SECTION
 	default 1024
 	depends on RAM_CONSOLE
 	help

drivers/console/ram_console.c

@@ -2,6 +2,7 @@
 
 /*
  * Copyright (c) 2015 Intel Corporation
+ * Copyright 2024 NXP
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -11,11 +12,26 @@
 #include <zephyr/sys/printk.h>
 #include <zephyr/device.h>
 #include <zephyr/init.h>
+#include <zephyr/linker/devicetree_regions.h>
+
+#ifdef CONFIG_RAM_CONSOLE_BUFFER_SECTION
+#if !DT_HAS_CHOSEN(zephyr_ram_console)
+#error "Lack of chosen property zephyr,ram_console!"
+#elif (CONFIG_RAM_CONSOLE_BUFFER_SIZE > DT_REG_SIZE(DT_CHOSEN(zephyr_ram_console)))
+#error "Custom RAM console buffer exceeds the section size!"
+#endif
+
+#define RAM_CONSOLE_BUF_ATTR	\
+	__attribute__((__section__(LINKER_DT_NODE_REGION_NAME(DT_CHOSEN(zephyr_ram_console)))))
+#else
+#define RAM_CONSOLE_BUF_ATTR
+#endif
 
 extern void __printk_hook_install(int (*fn)(int));
 extern void __stdout_hook_install(int (*fn)(int));
 
-char ram_console[CONFIG_RAM_CONSOLE_BUFFER_SIZE];
+char ram_console_buf[CONFIG_RAM_CONSOLE_BUFFER_SIZE] RAM_CONSOLE_BUF_ATTR;
+char *ram_console;
 static int pos;
 
 static int ram_console_out(int character)
@@ -28,6 +44,15 @@ static int ram_console_out(int character)
 
 static int ram_console_init(void)
 {
+#ifdef CONFIG_RAM_CONSOLE_BUFFER_SECTION
+	mm_reg_t ram_console_va;
+
+	device_map((mm_reg_t *)&ram_console_va, DT_REG_ADDR(DT_CHOSEN(zephyr_ram_console)),
+		   CONFIG_RAM_CONSOLE_BUFFER_SIZE, K_MEM_CACHE_NONE | K_MEM_DIRECT_MAP);
+	ram_console = (char *)ram_console_va,
+#else
+	ram_console = ram_console_buf,
+#endif
 	__printk_hook_install(ram_console_out);
 	__stdout_hook_install(ram_console_out);