Re: Parsing a bus fault message?

On Tue, Sep 28, 2010 at 09:26:51AM -0500, david.hagood@gmail.com wrote:

I finally found my problems accessing the PPC OWBAR registers as an
endpoint (copy/paste brown paper bag bug on my part), but I still get a
bus fault trying to access the device.

The problem is that I don't know if the fault is internal to the PPC (e.g.
I don't have something in the chip set up) or if the fault is happening on
the PCIe side of things.

Are there any good how-tos on interpreting the kernel machine check error
for the PPC, that might help me know where to look for the problem?


Alternatively, can somebody see a hint in the message that I don't know
enough to pick out? At this point, my code is trying to memcpy() from the
PCIe bus (mapped via the outbound ATMU) to local memory, so the fault is
either a) the ATMU is not accessible b) the ATMU is accessible but not
mapped (which I would have thought the ioremap call I made would have
handled) or c) the chip is not able to bus master on the PCI bus.


Machine check in kernel mode.
Caused by (from SRR1=149030): Transfer error ack signal

^^^ this is the line that contains some critical info

In the 86xx CPU manual, you should be able to find information about the
SRR1 register. Decoding the hex SRR1=0x149030 may help.

The kernel is telling you this is a TEA (transfer error acknowledge)
error. I've only seen this when I get an unhandled timeout on the local
bus. For example, a FPGA that has died in the middle of a request.

On the PCI bus, I haven't seen this error. The 83xx PCI controller is
smart enough to return 0xffffffff when reading a non-existent device.

I'm only familiar with 83xx, so I can't help too much on an 86xx board.
My best advice is: check your addresses. Make sure they're correct.

I assume that PCI on 86xx behaves similarly to 83xx. If you read from an
outbound window, your access gets translated into a PCI address and goes
onto the PCI bus. A good way of testing this is with the devmem utility
(part of busybox). It allows you to read/write any physical memory
location.

Using devmem will help you determine if the problem is in your code or
in your setup procedure.

I hope it helps,
Ira