I am having difficulty DMA'ing into sk_buffs. I have DMA code that works except when the destination is the data buffer in an sk_buff. No transfer error is reported in the status register but the sk_buff data buffer (the destination) is all zeros following the DMA while the source buffer is nonzero. I am running Linux 2.6.10 on an MPC8248.
These are classic symptoms of caching issues. My guess is because the DMA HW does the transfer of your data, the processor cache is not aware of the changes in actual memory. Try manually flushing / reloading your cache for the destination memory. BTW "dma_map_single /dma_unmap_single" does not work for some ppc architectures. So manually flush the cache using "flush_dcache_range"
Thank you for the suggestion. My problem turned out to be the program I was using to read memory was not able to read from the memory location of the DMA's destination. When I read the memory location within my driver I saw that the DMA was successful.
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