Hello, I have the following situation: 1. I'm using dma_alloc_coherent to allocate memory for DeviceA 2. I use DeviceA to fill the memory buffer. Everything is fine so far but at this point I would like to DMA the memory to DeviceB and I'm not sure the proper way of doing it. Is it allowed/ok/proper to call dma_map_single for DeviceB using the address returned from dma_alloc_coherent called on DeviceA? This seems to work fine in x86_64 but it feels like I'm breaking the rules because: 1. dma_map_single is supposed to be called with kmalloc addresses. 2. Since the address is from both dma_alloc_coherent and dma_map_single, I don't know if the dma_sync_* functions are necessary or not. I'm worried that I'm just getting lucky having this work and a future kernel update will break me since I'm not really following the rules. My code may eventually have to run on ARM too, and I'm not sure it would work. I have also considered: 1. Call dma_alloc_coherent for DeviceB and memcpy the data from DeviceA into it. This would work but I don't want the performance hit of double buffering. 2. Get rid of the the dma_alloc_coherent for deviceA use kmalloc/dma_map_single instead. This would work and maybe is the right thing to do. This requires the extra hassle of dma_sync_* functions which I was trying to avoid. Is there a better way of doing this that I'm missing? Thanks, Brian V.
