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 at 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?
