On Feb 4, 2009, at 12:48 PM, Benjamin Walsh wrote:
Hi Milton,
I've tracked it down to the device tree passed to the second kernel
being screwed-up when patched by kexec-tools. Namely, it was creating
linux,usable-memory entries that were wrong, and the MMU
initialization hung when it failed allocating for the page tables. I
hacked the tool, and got passed that point in the init sequence, but
the very first IO mapped access fails, so the MMU doesn't seem to be
set up correctly.
I would need more details exactly what you think is wrong.
How does it fail?
If the first IO mapped access fails, then I would ask if you are using
IOMMU. It is quite possible that the dart iommu code needs to be
modified to use the existing mapping table instead of allocating a new
table, otherwise any existing mappings being used by inflight dma would
fail and the that might cause mmio loads to wait for uncompletable dma
writes. Just a theory with the lack of information you gave me.
Anyway, up to my question: is the crash dump (kdump) kernel supposed
to use the memory reserved for it by the first kernel for its working
memory ? e.g. On that board, I have 0->2GB and 4->6GB for a total of
4GB of RAM. Let's say I reserve 1...@32m, that's 0x2000000->0xa000000.
Is the second kernel supposed to use
(0x2000000+<kernel size>) -> 0xa000000
for its memory pool and leave everything else:
0->0x2000000, 0xa000000 -> 80000000, 0x100000000 -> 0x180000000
as memory that is from the first kernel, used to debug it ?
Yes, but that is not quite how the device tree is formed.
The second kernel will also use the interrupt vector area at address 0.
Therefore that is saved as the backup region in purgatory to the
address allocated in the kdump region. The device tree is then
created with linux,usable-memory regions extending the kdump region
back to 0, and a reserve entry marking the area as reserved.
In addition, the device tree gets the memory backing tce tables for
pseries smp mode. It may need the page with the dart table, marked
reserved, so that the table gets added to the linear map -- except it
should be mapped cache inhibited so that may not work either.
Basically, I am trying to figure out if I patched the tool correctly.
Thanks,
Ben
On Sat, Jan 24, 2009 at 2:52 AM, Milton Miller <milt...@bga.com> wrote:
On Sat Jan 24 at 07:59:47 EST in 2009, Benjamin Walsh wrote:
I am trying to use kexec with a crash dump kernel on a Maple board
(Motorola
ATCA6101 to be precise). This board is running a two-CPU PPC970FX.
I am
running a 2.6.27-10 kernel and have tried both older kexec-tools
and the
newest ones. I have tried SMP and non-SMP kernels.
Once you start the second cpu it is likly executing instructions
somewhere.
Priory to 2.6.27 you had to compile a fixxed offset kerenl to run
kdump. With 2.6.27 that option was removed and replaced with teh
relocatable kerenl. However, becasue of the way linux interacts with
open firmware, the kernel will still move itself to 0 unless a
specific flag is set. The location of the flag was changed twice
during the merge process, and the patches for kexec-tools were not
made until early this year.
Using kexec -l to fast boot works correctly. However, loading a
crash dump
kernel and triggering a crash via echo c > /proc/sysrq-trigger
simply hangs
the board. I have traced the sequence down to after the call to
kexec_copy_flush(), when the CPU returns to real-address mode (bl
real_mode). At this point I have no further debugging information.
Two things could help me:
- Getting the fix if this is a known issue and a fix exists. I have
looked
at recent patches and nothing lept to mind, mostly relocatable
kernel
support.
That is a major change.
That said, I don't know if anyone has tested kexec panic beyond
pseries for 64 bit powerpc.
I know Paul originally prototyped the relocatable patch on a
powermac, but I dont' know what if any smp testing he performed.
And you said you are actualy on maple not a powermac, so the startup
issues are different.
- Obtaining the address of the serial port @3f8 in real mode. The
init
sequence with udbg ON says that the physical address of the port is
0xf40003f8; however, setting it up in poll mode and trying to stuff
characters in the tx buffer doesn't produce anything.
Ah yes. In real mode you can only talk to cacheable memory without
implementation specific assistance. However, if you look in the
kernel for the maple early udbg support, you will find the code you
need to talk to that serial port in real mode.
Has anyone recently tried to use the serial port in real mode ?
Thanks for any help.
Ben
Hope this gets you started. I wrote a lot of the kernel code, but I
had the advantage of external jtag access to the processor to see
where it when ended up when it went astray.
milton
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