[U-Boot-Users] Re: MPC8272ADS Hangs with gcc 4.0.0 and u-boot 1.1.4

[Addison Baldwin]

Thank you Wolfgang

Your advice was very useful. I got the board working! I would want to
submit a patch, but I'm not sure about what my modification can do in
the whole code. I suspect that there are other part(s) of the code
that suffer with new GCC 4 optimizations.

I started debugging with BDI2000. After a lot of steps, I found where
the board hanged. In fact, the processor resets in line 33 of
cpu/mpc8260.c, function m8260_cpm_reset()

line 33 : gd->dp_alloc_base = CPM_DATAONLY_BASE;

The gd variable was appointing to a wrong address. gd is a "register
volatile", as it is defined in include/asm-ppc/global_data.h:

#define DECLARE_GLOBAL_DATA_PTR     register volatile gd_t *gd asm ("r29")

Inspecting assembler generated code, I've found that before this
funcion, r29 should be initiated with the correct value. This should
be done in function cpu_init_f(), but no assembler code was generated
from the line that initialized gd:

void cpu_init_f (volatile immap_t * immr)
{
	DECLARE_GLOBAL_DATA_PTR;
	//register volatile gd_t *gd asm ("r29");
	
#if !defined(CONFIG_COGENT)		/* done in start.S for the cogent */
	uint sccr;
#endif
	volatile memctl8260_t *memctl = &immr->im_memctl;
	extern void m8260_cpm_reset (void);

	/* Pointer is writable since we allocated a register for it */
	gd = (gd_t *) (CFG_INIT_RAM_ADDR + CFG_GBL_DATA_OFFSET);

	/* Clear initial global data */
	memset ((void *) gd, 0, sizeof (gd_t));

....

So, I searched the web and found someone that was working with u-boot
and posted a possible GCC "optimization bug":

http://gcc.gnu.org/ml/gcc-bugs/2005-08/msg01984.html

And, in the end, a solution was given:

http://gcc.gnu.org/ml/gcc-bugs/2005-08/msg02003.html

This way, I modified the definition of DECLARE_GLOBAL_DATA_PTR to:

#define DECLARE_GLOBAL_DATA_PTR    register gd_t*volatile gd asm ("r29");

Now I compile the code and the board runs! But, for my surprise, a lot
of warnings are produced, like this:

cpu_init.c: In function 'cpu_init_f':
cpu_init.c:99: warning: volatile register variables don't work as you might wish

I know my new declaration can be wrong. But the old one seems to be wrong too.

Any idea?

Best Regards,
Addison Baldwin

On 2/2/06, Ron Kellam <ronkbox-news at yahoo.com> wrote:
> >If anyone had this problem, or if anyone have such a configuration
> >working (GCC 4 and U-Boot 1.1.4 with this board), any help will be
> >very appreciated.
>
> I have a custom board very similar to the MPC8272ADS, but without the
> BCSR FPGA.
>
> My board also hangs with u-boot 1.1.4 compiled with ELDK4.0's gcc 4,
> so the problem is not just the BCSR accesses.
>
> For now I'm sticking with my ELDK3.1.1 compiled u-boot, as I don't
> have time to debug u-boot when I have a working one.
>
> Could you please post your findings if you get to the bottom of it.
>
> Regards,
> Ron Kellam
>
>
>
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