Messages in this thread | | | Date | Tue, 16 Jun 2009 17:57:38 +0100 | From | Chris Pringle <> | Subject | Re: PowerPC PCI DMA issues (prefetch/coherency?) |
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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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