Hello,
Iam porting Linux 2.4.17 on MPC8260ADS. I had already working
Linux-2.4.1 version on MPC8260ADS board.
I have patched all the board specific changes to 2.4.17 and compiled.
When i loaded the image on board using PPCBOOT and run it, it hangs in
function "MMU_init_hw" (arch/ppc/mm/ppc_mmu.c) which is called from
MMU_init (arch/ppc/mm/init.c). And MMU_init is called from "_start_here"
subroutine in head.S file.
I had rather taken an tedious process of identifying the problem by
glowing LEDs present on the board. I have identify the location of the
problem.
Problem:
In "MMU_init_hw" function, it checks for this condition
"cur_cpu_spec[0]->cpu_features & CPU_FTR_HPTE_TABLE" and panics by
blinking leds in specific pattern after accessing the structure.
--- Code begins ---
if ((cur_cpu_spec[0]->cpu_features & CPU_FTR_HPTE_TABLE) == 0) {
/*
* Put a blr (procedure return) instruction at the
* start of hash_page, since we can still get DSI
* exceptions on a 603.
*/
hash_page[0] = 0x4e800020;
flush_icache_range((unsigned long) &hash_page[0],
(unsigned long) &hash_page[1]);
return;
}
--- Code ends ---
"cur_cpu_spec" is a array of pointer to cpu_spec structure
(include/asm-ppc/cputable.h) containing CPU related informations. I
understand that this is something to do with multiple processors system.
I checked the value of cur_cpu_spec[0] pointer. It was zero. At this
time, MMU would be ON with SDRAM located at 0xc0000000 (Logical
address). So when processor access this sructure which is pointing to 0
(outside physical memory boundary), it throws machine check exception
and calls panic function to display leds in specific pattern. This is
where iam stuck.
I also tried commenting this line as this was not there in 2.4.1
version. Here control went till this point in "head.S" code
--- Code start ---
/*
* Go back to running unmapped so we can load up new values
* for SDR1 (hash table pointer) and the segment registers
* and change to using our exception vectors.
*/
lis r4,2f at h
ori r4,r4,2f at l
tophys(r4,r4)
li r3,MSR_KERNEL & ~(MSR_IR|MSR_DR)
FIX_SRR1(r3,r5)
mtspr SRR0,r4
mtspr SRR1,r3
SYNC
RFI
/* Load up the kernel context */
2:
--- Code ends ---
After RFI instruction executed, it stops or hangs without any
indication. Expected result was control should jumps to label "2:" and
then branch to "load_up_mmu" function and "start_kernel" function.
I suspect cpu setup problem and may be MMU also.
Any help will be appreciated,
thanks in advance,
with rgds,
kamal
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