Scott Wood wrote:
Check asm/cputable.h for CPU_FTR_NEED_COHERENT. Make sure that
CONFIG_8260 is one of the #ifdefs that turns that on. It looks like
that was in place by 2.6.26 in arch/powerpc. I'm not sure what to
look for in arch/ppc.
I've just checked that and it's definitely switched on in CPU_FTR_COMMON
(CONFIG_8260 is also being used).
Also make sure that you park the bus on PCI and raise its arbitration
priority, as done at the end of fixup_pci in
arch/powerpc/boot/cuboot-pq2.c.
Since this is a reasonably recent kernel,
Not really, there was a fair amount of 82xx work in the mid-2.6.20s.
The addition of CPU_FTR_NEED_COHERENT to 82xx was somewhere in that time.
Can you try 2.6.30?
I'll give it a try, but that won't be a quick thing to do - will
hopefully manage to get that done tomorrow if it patches without too
many issues. I should point out that we've got the low latency patches
on this kernel too; I guess it'd be worth trying it without them before
I move kernels.
I'd guess that both of these things are correct. I've had a quick
look in that file and there is code in there raising arbitartion
priority and parking the bus.
Just because the code is there doesn't mean you're using it -- are you
using cuImage? Are you using arch/ppc or arch/powerpc?
Typically this would be done by firmware; it's only in cuboot because
u-boot wasn't doing it.
Just checked this is being called and it is. We're using arch/powerpc.
Interestingly, I've just turned off cache snooping and the problem
has got much worse. This has surprised me as I thought that part of
the job done by pci_map_sg was to flush the CPU cache
It only flushes the cache on hardware that doesn't do coherent DMA.
Ah right - that would explain what we're seeing then... Doh. Thought I
might have been onto something then. Is there any way to force a cache
flush? That'd at least prove it was a caching issue if it resolved the
problem.
Thanks,
Chris
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