Russell King - ARM Linux wrote: > On Sun, Feb 28, 2010 at 03:07:57PM +0100, Albert Herranz wrote: >> This patch makes part of the ARM dmabounce code available to other >> architectures as a generic API. > > There is already a generic dma bounce implementation - it's called > swiotlb - lib/swiotlb.c. We should eventually switch the ARM > dmabounce stuff over to that instead of keeping dmabounce around. > > The only problem I forsee is that on ARM, we have devices which can > only address the least significant N bits of RAM, but there may be > an offset on the base address of RAM on the bus which isn't included > in these N bits. > > Even more fun is where we have a DMA controller which can address > N bits of RAM, except for bit M which must be zero... (where N > M). > In the Wii we have several limitations: - it is a NOT_COHERENT_CACHE platform - write accesses to coherent memory from the main processor must be done always in 32-bit chunks - some devices can only reliably perform DMA to/from a specific region of memory (the second block of RAM, 64MB at 0x10000000, called MEM2) So if swiotlb is the way to go I can try to adapt it to take into account these cases: - it should allocate the io_tlb_start and io_tlb_overflow_buffer areas from MEM2 (add allocation/freeing hooks for these areas?) - it should copy data from coherent memory in 32-bit chunks (add copy to/from coherent hooks?) - it should decide to bounce buffers sitting in MEM1 (add a dma_needs_bounce() hook?) Thanks, Albert -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
