2.6.8.1 not booting on 405CR

2.6.8.1 not booting on 405CR

[Piotr Perak]

Hi.

We already have 2.4.23 kernel working on our board using IBM 405CR
processor. Now we're trying to start 2.6.8.1. But we have some strange
problems.

We use assembler intruction resetting the processor to see what is
executing (our breakpoint mechanism :) ). No metter what crosstool we use
the execuiton stops in same function. Here's the call stack.

setup_arch() - arch/ppc/kernel/setup.c
  -> ocp_early_init() - arch/ppc/syslib/ocp.c
    -> ocp_add_one_device() - arch/ppc/syslib/ocp.c
      ->  alloc_bootmem MACRO calling __alloc_bootmem_core() -
mm/bootmem.c

We added our "breakpoint" so __alloc_bootmem_core() looks like:

/* ... */
160	eidx = bdata->node_low_pfn - (bdata->node_boot_start >> PAGE_SHIFT);
161	asm ("mtspr 0x3f2, 12"); /* <-- our "breakpoint" */
162	offset = 0;
/* ... */

What is happening is that in working 2.4.23 kernel this code resets
processor, but in 2.6.8.1 it doesn't. This is very strange because the
assembler code generated in both is the same.

[root@localhost kernel]# powerpc-405-linux-gnu-objdump -S mm/bootmem.o >
asm

for kernel 2.4.23:
eidx = bdata->node_low_pfn - (bdata->node_boot_start >> PAGE_SHIFT);
338:   80 dd 00 00     lwz     r6,0(r29)
33c:   81 3d 00 04     lwz     r9,4(r29)
340:   54 c0 a3 3e     rlwinm  r0,r6,20,12,31
344:   7c e0 48 50     subf    r7,r0,r9
       asm ("mtspr 0x3f2, 12");
348:   7d 92 fb a6     mtdbcr0 r12
       offset = 0;

and for kernel 2.6.8.1:
eidx = bdata->node_low_pfn - (bdata->node_boot_start >> PAGE_SHIFT);
22c:   80 bf 00 00     lwz     r5,0(r31)
230:   81 3f 00 04     lwz     r9,4(r31)
234:   54 a0 a3 3e     rlwinm  r0,r5,20,12,31
238:   7d 80 48 50     subf    r12,r0,r9
       asm ("mtspr 0x3f2, 12");
23c:   7d 92 fb a6     mtdbcr0 r12
       offset = 0;

As you can see only used registers differ.

We moved eidx = bdata->node_low_pfn ... to the local variables definition
section so it looks like:
unsigned long eidx = bdata->node_low_pfn - (bdata->node_boot_start >>
PAGE_SHIFT);
and now the reset works in 2.6.8.1 too. Why? But then we move our
breakpoint to:

181	preferred = ((preferred + align - 1) & ~(align - 1)) >> PAGE_SHIFT;
182	preferred += offset;
183	areasize = (size+PAGE_SIZE-1)/PAGE_SIZE;
184     asm ("mtspr 0x3f2, 12");
185     incr = align >> PAGE_SHIFT ? : 1;

and it doesn't reset the processor. In 2.4.23 it does. We splitted 183
line into two and it resets then! But after we place reset instruction
after 185 line (incr = ...) it doesn't reset again! 

Anyone has any ideas? Anyone seen 2.6.8.1 kernel working on 405CR?




 

Re: 2.6.8.1 not booting on 405CR

[Benjamin Herrenschmidt]

On Thu, 2004-09-23 at 19:35, Piotr Perak wrote:
> Hi.
> 
> We already have 2.4.23 kernel working on our board using IBM 405CR
> processor. Now we're trying to start 2.6.8.1. But we have some strange
> problems.

I suggest you ask your question on the linuxppc-dev list (or better,
linuxppc-embedded, but that one was just re-created from the old
dead listserver so people may not be subscribed yet).

Look for those on http://ozlabs.org/mailman/listinfo

Ben.