> > Tim> I'm using an MVME6100 with Linux 2.6.14 and experiencing what I > Tim> think is a cache coherency problem. An external PCIX master > Tim> performs a DMA transfer of a well known data pattern into SDRAM, > Tim> but when the device driver goes to look at the data it is mostly > Tim> okay, but occasionally has garbage. > > If the hardware is reliable, I think you are right. The cache > coherency problem.
The hardware is reliable. > > Tim> 1) Should the processor bus cache snooping actually work on an > Tim> MVME6100? > Tim> E.g. is it correct that CONFIG_NOT_COHERENT_CACHE is undefined? > > Yes, you can undefine the CONFIG_NOT_COHERENT_CACHE, but you > must make sure the host bridge did the snooping setup for PCI > inbound transaction. > If you setup the snooping window, I think the host bridge > will assert /GLB signal to processor. The processor will > snoop the 60x/MPX bus to keep cache coherence. > Ah. This must be the problem. I have a few PCI devices, and on one of them it looked like snooping was working. I just assumed the other device was setup correctly. > Also, you can define the CONFIG_NOT_COHERENT_CACHE, then you > are assuming The system has not hardware coherency. You need > use the software to keep the cache coherency. > I tried this, and got compiler errors. > > Tim> 2) If this really is a cache coherency problem, are there other > Tim> cache management functions available in ppc linux besides the > Tim> dma_cache_inv, dma_cache_wback, dma_cache_wback_inv > macros I should > Tim> be looking at? > > I think it is a cache coherency problem, if you define the > CONFIG_NOT_COHERENT_CACHE You can get these functions, dma_map_single > I added some inline assembly dcbi/dcbf (invalidate/flush) instructions to the particular code in question, and the problems went away. So definitely a cache problem. As I said above, defining CONFIG_NOT_COHERENT_CACHE causes compiler errors, so I'm going to look into this more. I suppose whatever file implements the include/linux/dma-mapping.h stuff isn't BSP specific, so its probably just not being compiled in? Will look into it. Thanks for you help, Tim
