board: Add QEMU m68k virt board support

Add support for the QEMU 'virt' machine on the m68k architecture. This
board emulates a generic machine based on the Motorola 68040 CPU
equipped with Goldfish virtual peripherals.

Introduce the necessary board configuration and initialization
infrastructure. The implementation includes logic to parse the QEMU
bootinfo interface, enabling dynamic detection of system RAM size to
adapt to the virtual machine's configuration.

Enable the Goldfish TTY driver for serial console output. Additionally,
enable Goldfish RTC and timer drivers to support real-time clock
functionality and nanosecond-resolution delays. Include comprehensive
documentation covering build instructions and usage examples.

Signed-off-by: Kuan-Wei Chiu <[email protected]>
Tested-by: Daniel Palmer <[email protected]>
Reviewed-by: Simon Glass <[email protected]>

2 files changed, 40 insertions, 0 deletions

diff --git a/doc/board/emulation/index.rst b/doc/board/emulation/index.rst
index f8908166276..4f7c812d493 100644
--- a/doc/board/emulation/index.rst
+++ b/doc/board/emulation/index.rst
@@ -15,6 +15,7 @@ Emulation
    qemu-sbsa
    qemu-x86
    qemu-xtensa
+   qemu-m68k
 
 Also see
 
diff --git a/doc/board/emulation/qemu-m68k.rst b/doc/board/emulation/qemu-m68k.rst
new file mode 100644
index 00000000000..6c4de54cf6a
--- /dev/null
+++ b/doc/board/emulation/qemu-m68k.rst
@@ -0,0 +1,39 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+.. Copyright (C) 2025, Kuan-Wei Chiu <[email protected]>
+
+QEMU m68k
+=========
+
+QEMU for m68k supports a special 'virt' machine designed for emulation and
+virtualization purposes. This document describes how to run U-Boot under it.
+
+The QEMU virt machine models a generic m68k virtual machine with Goldfish
+interfaces. It supports the Motorola 68040 CPU architecture.
+
+Building U-Boot
+---------------
+Set the CROSS_COMPILE environment variable to your m68k toolchain, and run:
+
+.. code-block:: bash
+
+    export CROSS_COMPILE=m68k-linux-gnu-
+    make qemu-m68k_defconfig
+    make
+
+Running U-Boot
+--------------
+The minimal QEMU command line to get U-Boot up and running is:
+
+.. code-block:: bash
+
+    qemu-system-m68k -M virt -cpu m68040 -nographic -kernel u-boot
+
+Note that the `-nographic` option is used to redirect the console to stdio,
+which connects to the emulated Goldfish TTY device.
+
+Hardware Support
+----------------
+The following QEMU virt peripherals are supported in U-Boot:
+
+* Goldfish TTY (Serial Console)
+* Goldfish RTC (Real Time Clock)