* Alan Stern | 2011-07-30 09:03:50 [-0400]: >> Sounds like it is a arch dependent problem, and not much related with usb. > >Yes indeed. Coherent buffers are allocated in uncached memory on some >architectures, which makes them very expensive to access. But other >architectures can use cached memory, which makes coherent buffers >less expensive than non-coherent ones since no DMA mapping is required. > >This makes for a difficult tradeoff. Historically, I think the balance >in USB has been tipped in favor of x86. > >For something as time-critical as uvcvideo, it might make sense for the >driver to implement both options in arch-dependent code. What about using kmalloc() + dma_map_single() + dma_unmap_single() instead of arch dependend code in drivers? Those are nops x86 and perform the required syncs on other architectures. > >Alan Stern > Sebastian -- 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
