[PATCH v2 2/4] m68k: Add support for M68040 CPU

Kuan-Wei Chiu
2025-12-26T23:04:07Z

Add support for the Motorola 68040 architecture. Currently, m68k
support in U-Boot is primarily focused on ColdFire variants. Introduce
the necessary infrastructure to support the classic M680x0 series,
specifically targeting the M68040 as emulated by QEMU.

The implementation includes exception vectors, early startup code, and
minimal CPU initialization and relocation stubs. It also defines the
standard m68k boot information structure used for passing hardware
information to the operating system. To ensure compatibility, ColdFire-
specific library objects such as cache and interrupt handling are
excluded from the build when M68040 is selected.

Additionally, apply a specific workaround during the early memory
reservation stage. Use a manual loop to clear global data instead of
the standard memset() function, as utilizing memset() at this point was
observed to cause a hang on the QEMU platform.

Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
---
Changes in v2:
- Update SPDX license identifier to GPL-2.0-or-later.
- Sort header inclusions alphabetically.
- Separate MAINTAINERS entry for the M680x0 architecture.
- Fix tabs vs spaces in Kconfig.
- Rename arch/m68k/cpu/m68040 to arch/m68k/cpu/m680x0 to separate the
architecture family from the specific CPU model.
- Introduce M680x0 Kconfig symbol for the architecture family, selected
by M68040.

MAINTAINERS | 6 +++
arch/m68k/Kconfig | 16 +++++++
arch/m68k/Makefile | 1 +
arch/m68k/config.mk | 10 ++++-
arch/m68k/cpu/m680x0/Makefile | 6 +++
arch/m68k/cpu/m680x0/cpu.c | 77 ++++++++++++++++++++++++++++++++
arch/m68k/cpu/m680x0/start.S | 73 ++++++++++++++++++++++++++++++
arch/m68k/cpu/m680x0/u-boot.lds | 47 +++++++++++++++++++
arch/m68k/include/asm/bootinfo.h | 31 +++++++++++++
arch/m68k/lib/Makefile | 9 ++--
10 files changed, 268 insertions(+), 8 deletions(-)
create mode 100644 arch/m68k/cpu/m680x0/Makefile
create mode 100644 arch/m68k/cpu/m680x0/cpu.c
create mode 100644 arch/m68k/cpu/m680x0/start.S
create mode 100644 arch/m68k/cpu/m680x0/u-boot.lds
create mode 100644 arch/m68k/include/asm/bootinfo.h

diff --git a/MAINTAINERS b/MAINTAINERS
index da4a6e4d518..d0ae9134551 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1306,6 +1306,12 @@ F: lib/getopt.c
F: test/log/
F: test/py/tests/test_log.py

+M680X0 ARCHITECTURE
+M: Kuan-Wei Chiu <visitorckw@gmail.com>
+S: Maintained
+F: arch/m68k/cpu/m680x0/
+F: arch/m68k/include/asm/bootinfo.h
+
MALI DISPLAY PROCESSORS
M: Liviu Dudau <liviu.dudau@foss.arm.com>
S: Supported
diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
index 8ade6f7b9d1..de7c673c376 100644
--- a/arch/m68k/Kconfig
+++ b/arch/m68k/Kconfig
@@ -56,6 +56,9 @@ config MCF5441x
select DM_SERIAL
bool

+config M680x0
+ bool
+
# processor type
config M5208
bool
@@ -110,6 +113,10 @@ config M54418
bool
select MCF5441x

+config M68040
+ bool
+ select M680x0
+
# peripherals
config CF_DSPI
bool
@@ -178,6 +185,15 @@ config TARGET_STMARK2

endchoice

+config SYS_CPU
+ string
+ default "mcf52x2" if MCF52x2
+ default "mcf523x" if MCF523x
+ default "mcf530x" if MCF530x
+ default "mcf532x" if MCF532x
+ default "mcf5445x" if MCF5445x
+ default "m680x0" if M680x0
+
source "board/BuS/eb_cpu5282/Kconfig"
source "board/cobra5272/Kconfig"
source "board/freescale/m5208evbe/Kconfig"
diff --git a/arch/m68k/Makefile b/arch/m68k/Makefile
index 4a7960bbeb4..bb57cf9ac63 100644
--- a/arch/m68k/Makefile
+++ b/arch/m68k/Makefile
@@ -17,6 +17,7 @@ cpuflags-$(CONFIG_M5307) := -mcpu=5307
cpuflags-$(CONFIG_MCF5301x) := -mcpu=53015 -fPIC
cpuflags-$(CONFIG_MCF532x) := -mcpu=5329 -fPIC
cpuflags-$(CONFIG_MCF5441x) := -mcpu=54418 -fPIC
+cpuflags-$(CONFIG_M68040) := -mcpu=68040 -fno-pic

PLATFORM_CPPFLAGS += $(cpuflags-y)

diff --git a/arch/m68k/config.mk b/arch/m68k/config.mk
index 643b7d1d35d..458953f9712 100644
--- a/arch/m68k/config.mk
+++ b/arch/m68k/config.mk
@@ -3,8 +3,14 @@
# (C) Copyright 2000-2002
# Wolfgang Denk, DENX Software Engineering, wd@denx.de.

-PLATFORM_CPPFLAGS += -D__M68K__ -fPIC
+PLATFORM_CPPFLAGS += -D__M68K__
+ifneq ($(CONFIG_M680x0),y)
+PLATFORM_CPPFLAGS += -fPIC
+endif
KBUILD_LDFLAGS += -n -pie
PLATFORM_RELFLAGS += -ffunction-sections -fdata-sections
-PLATFORM_RELFLAGS += -ffixed-d7 -msep-data
+PLATFORM_RELFLAGS += -ffixed-d7
+ifneq ($(CONFIG_M680x0),y)
+PLATFORM_RELFLAGS += -msep-data
+endif
LDFLAGS_FINAL += --gc-sections -pie
diff --git a/arch/m68k/cpu/m680x0/Makefile b/arch/m68k/cpu/m680x0/Makefile
new file mode 100644
index 00000000000..f6e0c9a46c0
--- /dev/null
+++ b/arch/m68k/cpu/m680x0/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+#
+# Copyright (C) 2025, Kuan-Wei Chiu <visitorckw@gmail.com>
+
+extra-y += start.o
+obj-y += cpu.o
diff --git a/arch/m68k/cpu/m680x0/cpu.c b/arch/m68k/cpu/m680x0/cpu.c
new file mode 100644
index 00000000000..15e0c30980a
--- /dev/null
+++ b/arch/m68k/cpu/m680x0/cpu.c
@@ -0,0 +1,77 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * CPU specific code for m68040
+ *
+ * Copyright (C) 2025, Kuan-Wei Chiu <visitorckw@gmail.com>
+ */
+
+#include <asm/global_data.h>
+#include <config.h>
+#include <cpu_func.h>
+#include <init.h>
+#include <linux/types.h>
+#include <stdio.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+void m68k_virt_init_reserve(ulong base)
+{
+ struct global_data *gd_ptr = (struct global_data *)base;
+ char *p = (char *)gd_ptr;
+ unsigned int i;
+
+ /* FIXME: usage of memset() here caused a hang on QEMU m68k virt. */
+ for (i = 0; i < sizeof(*gd_ptr); i++)
+ p[i] = 0;
+
+ gd = gd_ptr;
+
+ gd->malloc_base = base + sizeof(*gd_ptr);
+}
+
+int print_cpuinfo(void)
+{
+ puts("CPU: M68040 (QEMU Virt)\n");
+ return 0;
+}
+
+int get_clocks(void)
+{
+ return 0;
+}
+
+int cpu_init_r(void)
+{
+ return 0;
+}
+
+/*
+ * Relocation Stub
+ * We skip actual relocation for this QEMU bring-up and jump directly
+ * to board_init_r.
+ */
+
+void relocate_code(ulong sp, struct global_data *new_gd, ulong relocaddr)
+{
+ board_init_r(new_gd, relocaddr);
+}
+
+/* Stubs for Standard Facilities (Cache, Interrupts, Timer) */
+
+int disable_interrupts(void) { return 0; }
+void enable_interrupts(void) { return; }
+int interrupt_init(void) { return 0; }
+
+void icache_enable(void) {}
+void icache_disable(void) {}
+int icache_status(void) { return 0; }
+void dcache_enable(void) {}
+void dcache_disable(void) {}
+int dcache_status(void) { return 0; }
+void flush_cache(unsigned long start, unsigned long size) {}
+void flush_dcache_range(unsigned long start, unsigned long stop) {}
+
+int timer_init(void) { return 0; }
+unsigned long timer_read_counter(void) { return 0; }
+ulong get_tbclk(void) { return 1000000; }
+void __udelay(unsigned long usec) {}
diff --git a/arch/m68k/cpu/m680x0/start.S b/arch/m68k/cpu/m680x0/start.S
new file mode 100644
index 00000000000..0802ca1fca2
--- /dev/null
+++ b/arch/m68k/cpu/m680x0/start.S
@@ -0,0 +1,73 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Startup code for m68040
+ *
+ * Copyright (C) 2025, Kuan-Wei Chiu <visitorckw@gmail.com>
+ */
+
+#include <asm-offsets.h>
+#include <config.h>
+#include <linux/linkage.h>
+
+.section .text
+
+/*
+ * Vector Table
+ * m68k uses the first 1KB for the exception vector table.
+ */
+.balign 4
+.global _vectors
+_vectors:
+ .long CFG_SYS_INIT_SP_ADDR /* 0x00: Initial SP */
+ .long _start /* 0x04: Initial PC (Reset) */
+ .long _fault /* 0x08: Bus Error */
+ .long _fault /* 0x0C: Address Error */
+ .long _fault /* 0x10: Illegal Instruction */
+ .long _fault /* 0x14: Zero Divide */
+ .long _fault /* 0x18: CHK */
+ .long _fault /* 0x1C: TRAPV */
+ .long _fault /* 0x20: Privilege */
+ .long _fault /* 0x24: Trace */
+ .long _fault /* 0x28: Line 1010 */
+ .long _fault /* 0x2C: Line 1111 */
+ .fill 0x400 - (.-_vectors), 1, 0
+
+/*
+ * Entry Point
+ */
+ENTRY(_start)
+ /* Disable Interrupts */
+ move.w #0x2700, %sr
+
+ /* Setup initial stack pointer */
+ move.l #CFG_SYS_INIT_SP_ADDR, %sp
+
+ /*
+ * Allocate Global Data (GD)
+ * board_init_f_alloc_reserve(top) returns the new top of stack in %d0
+ */
+ move.l %sp, -(%sp)
+ bsr.l board_init_f_alloc_reserve
+ addq.l #4, %sp
+
+ /* Update Stack Pointer and set GD register */
+ move.l %d0, %sp
+ move.l %d0, %d7 /* %d7 is the gd register */
+
+ /* Initialize Reserved Memory. */
+ move.l %d0, -(%sp)
+ bsr.l m68k_virt_init_reserve
+ addq.l #4, %sp
+
+ /* Enter board_init_f(0) */
+ clr.l -(%sp)
+ bsr.l board_init_f
+ addq.l #4, %sp
+
+ /* Should not return */
+hang:
+ bra.s hang
+ENDPROC(_start)
+
+_fault:
+ bra.s _fault
diff --git a/arch/m68k/cpu/m680x0/u-boot.lds b/arch/m68k/cpu/m680x0/u-boot.lds
new file mode 100644
index 00000000000..ae102c32833
--- /dev/null
+++ b/arch/m68k/cpu/m680x0/u-boot.lds
@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Linker Script for m68040
+ *
+ * Copyright (C) 2025, Kuan-Wei Chiu <visitorckw@gmail.com>
+ */
+
+OUTPUT_ARCH(m68k)
+ENTRY(_start)
+
+SECTIONS
+{
+ . = 0x00000000;
+ __text_start = .;
+
+ .text :
+ {
+ arch/m68k/cpu/m680x0/start.o (.text*)
+ *(.text*)
+ }
+
+ . = ALIGN(16);
+ .rodata : { *(.rodata*) }
+
+ . = ALIGN(16);
+ .data : { *(.data*) }
+
+ . = ALIGN(4);
+ .u_boot_list : {
+ KEEP(*(SORT(*u_boot_list*)));
+ }
+
+ . = ALIGN(4);
+ __image_copy_end = .;
+ __init_end = .;
+
+ . = ALIGN(16);
+ __bss_start = .;
+ .bss :
+ {
+ *(.bss*)
+ . = ALIGN(16);
+ }
+ __bss_end = .;
+
+ _end = .;
+}
diff --git a/arch/m68k/include/asm/bootinfo.h b/arch/m68k/include/asm/bootinfo.h
new file mode 100644
index 00000000000..3d2ec818257
--- /dev/null
+++ b/arch/m68k/include/asm/bootinfo.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2025, Kuan-Wei Chiu <visitorckw@gmail.com>
+ *
+ * Definitions for the m68k bootinfo interface.
+ */
+
+#ifndef _ASM_M68K_BOOTINFO_H
+#define _ASM_M68K_BOOTINFO_H
+
+#ifndef __ASSEMBLY__
+
+struct bi_record {
+ unsigned short tag; /* tag ID */
+ unsigned short size; /* size of record (in bytes) */
+ unsigned long data[0]; /* data */
+};
+
+#endif /* __ASSEMBLY__ */
+
+/* Bootinfo Tag IDs */
+#define BI_LAST 0x0000
+#define BI_MACHTYPE 0x0001
+#define BI_CPUTYPE 0x0002
+#define BI_FPUTYPE 0x0003
+#define BI_MMUTYPE 0x0004
+#define BI_MEMCHUNK 0x0005
+#define BI_RAMDISK 0x0006
+#define BI_COMMAND_LINE 0x0007
+
+#endif /* _ASM_M68K_BOOTINFO_H */
diff --git a/arch/m68k/lib/Makefile b/arch/m68k/lib/Makefile
index 6e1fd938f52..e62de51f260 100644
--- a/arch/m68k/lib/Makefile
+++ b/arch/m68k/lib/Makefile
@@ -7,10 +7,7 @@
## if the user asked for it
lib-$(CONFIG_USE_PRIVATE_LIBGCC) += lshrdi3.o muldi3.o ashldi3.o ashrdi3.o

-obj-y += bdinfo.o
obj-$(CONFIG_CMD_BOOTM) += bootm.o
-obj-y += cache.o
-obj-y += interrupts.o
-obj-y += time.o
-obj-y += traps.o
-obj-y += fec.o
+ifndef CONFIG_M680x0
+obj-y += cache.o interrupts.o time.o traps.o bdinfo.o fec.o
+endif
--
2.52.0.358.g0dd7633a29-goog