Re: [PATCH v5 4/7] m68k: Add support for M68040 CPU

[Kuan-Wei Chiu <visitorckw@gmail.com>]

Hi Simon,

On Mon, Jan 05, 2026 at 04:30:29PM -0700, Simon Glass wrote:
> Hi Kuan-Wei,
> 
> On Mon, 5 Jan 2026 at 11:20, Kuan-Wei Chiu <visitorckw@gmail.com> wrote:
> >
> > 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 v5:
> > - Rebase on u-boot/next branch.
> >
> >  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       | 72 +++++++++++++++++++++++++++++++
> >  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, 263 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 efecb213be7..bf85f642a8d 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -1324,6 +1324,12 @@ 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
> 
> How about a comment as to what this is?

I will add help text to explain that this targets the classic Motorola
680x0 series.

> 
> > +
> >  # 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..e2974560f4d
> > --- /dev/null
> > +++ b/arch/m68k/cpu/m680x0/cpu.c
> > @@ -0,0 +1,72 @@
> > +// 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;
> 
> Eek!
> 
> > +
> > +       gd = gd_ptr;
> > +
> > +       gd->malloc_base = base + sizeof(*gd_ptr);
> > +}
> > +
> > +int print_cpuinfo(void)
> > +{
> > +       puts("CPU:   M68040 (QEMU Virt)\n");
> 
> We normally put a blank line before the final return (unless it is the
> only code in the function).

Ack. Will fix.

> 
> > +       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);
> 
> Why skip relocation?

As Daniel noted in his review of v2, he has a working implementation
for relocation.

To keep this initial port simple, we decided to defer the relocation
support. Since qemu loads U-Boot directly into ram, running in-place
works sufficient for now. We plan to integrate Daniel's relocation code
in a future patch series.

> 
> > +}
> > +
> > +/* Stubs for Standard Facilities (Cache, Interrupts) */
> > +
> > +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) {}
> > 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
> 
> Is there a Kconfig you could use to group these files? Then it could
> be enabled if !M680x0

Maybe let's add a new hidden Kconfig symbol CONFIG_ARCH_COLDFIRE which
will be selected by the existing coldfire platforms. Then I can use
obj-$(CONFIG_ARCH_COLDFIRE) to group these files.

Regards,
Kuan-Wei

> > --
> > 2.52.0.358.g0dd7633a29-goog
> >
> 
> Regards,
> Simon