On Wed, 2010-02-17 at 10:15 +0100, Oliver Neukum wrote: > We should have changed the subject line. > > There's a second problem. It turns out that on ARM > mapping for DMA must not be done if PIO will be used. Some HCDs > use PIO for some transfers but DMA for others. The generic layer > must learn about this. Ah, that makes a lot of sense and the same problem would happen on any non-DMA coherent architecture, including some embedded ppc's. I can see why the dma unmap would invalidate the dcache and blow away the PIO. What bugs me here is that the dma_map_* operation should always be done at the lowest level, ie, the actual HCD driver, and thus it should be up to the HCD to decide whether to dma_map or not depending on whether it's going to do DMA or not. I haven't scrutinized USB lately but if that isn't the case and the dma_map_* operations are done behind your back by the USB core then that needs to be changed in a way or another, or hooked at least. Cheers, Ben. -- 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
