Virtex-II Pro tlbia exception

[Kerl, John]

Hello all,

After several weeks on other projects I am picking up on
the VII-Pro again.

For reference, we have our firmware up and running fine on
the board; we can talk to the UART, and SDRAM tests fine.
(The hardware-level verification is actually something we are
good at doing.)

Using arch/ppc/boot/avnet (modified from arch/ppc/boot/common),
along with our firmware, I'm able to build a zImage.initrd.elf,
TFTP to the board, and jump into arch/ppc/boot/avnet/misc-embedded.c.
This code reports on the bd_t parameters passed from the firmware
(all parameters are as expected), and decompresses the kernel to
address 0.  I can hex-dump the address-0 region & I find that
what I see in vmlinux on the host PC really is what I see at
address 0 and above.

Then the arch/ppc/boot code jumps to address 0, entering vmlinux
per se.  The first few instructions (head_4xx.S) save boot args
r3-r7 to r31-27, then jump to initial_mmu.  The very first thing
there is a tlbia.

Now, when I single-step through this, I find that the debugger
(XMD) shows me tlbia being executed twice (e.g. "stp" once and
I'm still at the tlbia, "stp" again and continue), and also
the next instruction after that is fetched from address 0xedba0700.

Now, the 0xedba0000 prefix is, as far as I can tell, garbage.
8xx's have an MSR bit that specifies whether exception prefixes
are 0x00000000 or 0xfff00000; I see no such bit for the VII-Pro 405.
And the 0700 suffix looks like a program check; yet, my MSR is 00000000
indicating that I am indeed in privileged mode.  SRR0 is just the
address of the tlbia.

Since I've been running simple-minded firmware up to this point, I
think it highly likely that I haven't yet told the 405 to be in
some mode it needs to be in.  But I don't know what.  I checked
around in PPCBoot source for the ML2 board, thinking that perhaps
someone else porting to Virtex-II Pro might have found some magic
ingredient, but actually the initialization there appears to be
minimal (as expected).

Does anyone know why (a) the prefix 0xedba is so bizarre, (b)
why I appear to be taking a program check, and/or (c) am I
missing some initialization steps that the firmware should
have done?

Thanks.

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/