On Thu, 2015-03-19 at 20:25 -0700, Keith Packard wrote: > > That is a violation of the DMA rules on non-coherent architectures. > > The buffer must be allocated separately. > > Ok, I'm not sure I understand the reasoning given that both come from > kmalloc, but that's easy to do. That happens on non-coherent architectures. Suppose you do DMA into a buffer. The data will go into RAM and only into RAM (by definition). So if you evaluate the buffer you must read from RAM, not the cache. To assure that we write out and invalidate the cache line. If, however, you read or write into the same cache line the CPU will cache the buffer again. And if the line is laundered after the DMA, the old content is written back. kmalloc() on those architectures guarantees that separate allocations don't share a cache line. Regards Oliver -- 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
