Hi Greg,

On 10/08/2017 09:06, Greg Ungerer wrote:
Hi Angelo,

On 10/08/17 01:32, Angelo Dureghello wrote:
[snip]
sure, on this board  http://sysam.it/cff_stmark2.html
there are 128MB of ddr2.

External SDRAM is accessible, at least without any mmc support enabled,
from 0x40000000.

I have following test config:

   GNU nano 2.8.6                                                               
               File: arch/m68k/configs/stmark2_defconfig

CONFIG_LOCALVERSION="stmark2-001"
[snip]


I tried still yesterday a bit, but seems there is no much support for
earlyprintk / low level debug for this architecture.

In case i can try with a gpio toggling routine, at least to find
where kernel stops.

The attached patch, is a quick and dirty early console output method.
It works for me on the m5475, should work for you "as is" on the 5441x too.

It is kind of an early printk. Of course it still needs the early
kernel boot to have succeeded before you will get anything much coming out.
But it is worth trying.

Ok many thanks. Btw i used a __square(); function written in asm, so i am
sure i see the gpio toggling in very early stages.


I am wondering if the non-0 base RAM may be a problem. I have only run
the MMU enabled code on platforms with 0 based RAM so far. But lets see if
the early console trace attached gives us anything before digging into that.


This MCU has sdram area physically mapped at 0x4000 0000 so U-Boot, to be
able to execute the kernel must load it to that location/area anyway.

But i have seen that it is not a problem, after MMU is enabled in head.S
the jump
movel #_vstart,%a0 /* jump to "virtual" space */
        jmp     %a0@

works fine. Since that range is not hitting anything that is maintained
physical, it can be translated into virtual without any issue.

After some hard debug, i see the execution stops at:

asmlinkage __visible void __init start_kernel(void)
   ...
   setup_arch(&command_line);      setup_mm.c
      ...
      paging_init();               mm/mcfmmu.c
         ...
         empty_zero_page = (void *) alloc_bootmem_pages(PAGE_SIZE);
         ^line 47 mcfmmu.c

Inside alloc_bootmem_pages(), execution seems to end up finally to
mm/bootmem.c and likely to alloc_bootmem_bdata().
In case i can still proceed to find the exact place where execution stops,
but i suspect in the while(1), line 545.

As a curious thing, i find in a different cf CPU code "m54xx.c"
the following:

void __init config_BSP(char *commandp, int size)
{
#ifdef CONFIG_MMU
        cf_bootmem_alloc();
        mmu_context_init();
#endif
        
Do also m5441x.c maybe need this calls ?

Would be very nice to have MMU working. Strangely, i don't see any
board_config with it enabled. Was it ever tested on some Coldfire ?
Waiting your suggestion on how to proceed.

Regards,
Angelo Dureghello
Regards
Greg

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