On Tue, Apr 12, 2011 at 11:06:34PM +0200, Janusz Krzysztofik wrote: > The patch tries to solve this regression by using > virt_to_phys(bus_to_virt(mem->dma_handle)) instead of problematic > virt_to_phys(mem->vaddr). Who says that DMA handles are bus addresses in the strictest sense? DMA handles on ARM are the bus address to program 'dev' with in order for it to access the memory mapped by dma_alloc_coherent(). On some ARM platforms, this bus address is dependent on 'dev' - such as platforms with more than one root PCI bus, and so bus_to_virt() just doesn't hack it. What is really needed is for this problem - the mapping of DMA coherent memory into userspace - to be solved with a proper arch API rather than all these horrible hacks which subsystems instead invent. That's something I tried to do with the dma_mmap_coherent() stuff but it was shot down by linux-arch as (iirc) PA-RISC objected to it. Hence why ARM only implements it. Maybe the video drivers should try to resurect the idea, maybe only allowing this support for architectures which provide dma_mmap_coherent(). -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
