[OpenBIOS] ppc64 MMU issues (was: ppc(64) debugging)
andreas.faerber at web.de
Sun Nov 7 23:13:39 CET 2010
Am 01.11.2010 um 17:36 schrieb Andreas Färber:
> Latest state with local patches is that hell breaks loose once the
> MMU is set up. I get a 0x400 (ISI) exception and when the bctrl to
> isi_exception() is executed, we end up at trap_error, where it
> branches to unexpected_excep() and tries to printk() to the serial
> port that's not yet set up. I'll put a few patches together.
Since r945 everything except for the trampoline issue should be in SVN.
I've made no more progress throughout the week though:
Directly after we set the MSR_IR|MSR_DR bits in the MSR (arch/ppc/qemu/
ofmem.c:setup_mmu), we get an ISI exception and end up in arch/ppc/
qemu/start.S:vector__0x400 (the 0xfffxxxxx one). We proceed up to the
bctrl which should take us to arch/ppc/qemu/ofmem.c:isi_exception, but
then get a 0x700 program exception. The value in ctr looks sensible,
it's some 0xfffxxxxx address.
i) I read that mtsrin were not allowed in 64-bit mode and its results
unpredictable, so I tried switching MSR_SF off before and back on
after the loop, without luck.
ii) If I exit the setup_mmu() function without turning the MMU on, we
proceed to arch/ppc/qemu/init.c:entry() but are unsuccessful reading
the magic fw_cfg signature. Stepping through the code it seemed as if
some variable assignments like in drivers/fw_cfg.c:fw_cfg_init() were
having no effect - could that be due to OpenBIOS code execution
happening in ROM rather than ea_to_phys()-mapped to RAM? (i.e., write-
only storage?:)) Or would this be some memory caching issue for the
iii) Before turning on the MMU, I tried implementing the early-mapping
of pages by calling hash_page() from ofmem_arch_early_map_pages() and
calling ofmem_map() for the ROM-to-RAM translation and for identity-
mapping the code. This leads to a hang in libopenbios/
ofmem_common.c:ofmem_update_memory_available() in a code path (a
printk in ofmem_realloc()) that would normally only be taken if
libopenbios/ofmem_common.c:s_phandle_memory were non-zero, at a point
where it should still be zero.
Any clue why ppc works but ppc64 doesn't?
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