Tim> I'm using an MVME6100 with Linux 2.6.14 and experiencing what Tim> I think is a cache coherency problem. An external PCIX Tim> master performs a DMA transfer of a well known data pattern Tim> into SDRAM, but when the device driver goes to look at the Tim> data it is mostly okay, but occasionally has garbage.
If the hardware is reliable, I think you are right. The cache coherency problem. Tim> I'm allocating the memory using alloc_skb, then giving a PCI Tim> translated pointer to the PCIX master. Since I think it is a Tim> cache coherency problem, I tried to use the dma_cache_inv Tim> macro to invalidate the cache before looking at the data, but Tim> realized that for this board, that function does nothing Tim> since CONFIG_NOT_COHERENT_CACHE is undefined. So Tim> questions: If the CONFIG_NOT_COHERENT_CACHE is not set. You are assuming and using the hardware cache coherency mechanism. Tim> 1) Should the processor bus cache snooping actually work on Tim> an 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. 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. Tim> 1a) Does this type of bus snooping work when a bus master Tim> physically external to the PowerPC chip is doing the transfer? As above, you must tell the bridge what address need snoop. If you did, The proceesor will do snooping. Tim> 2) If this really is a cache coherency problem, are there Tim> other cache management functions available in ppc linux Tim> besides the dma_cache_inv, dma_cache_wback, Tim> dma_cache_wback_inv macros I should 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 -Dave
