Hi Florian, On Friday 12 December 2014 12:52:49 Florian Echtler wrote: > On 11.12.2014 20:36, Alan Stern wrote: > > On Sun, 7 Dec 2014, Florian Echtler wrote: > >> - Can I always use DMA on the USB side (for bulk transfers), or does > >> this in any way require support from the USB device's hardware? (I'm > >> guessing no, but a definite answer would be great.) > > > > DMA requires hardware support in the USB host controller, not in the > > USB device. Most current USB host controllers support DMA; only a few > > of the oldest ones don't. > > thanks - good to know for sure. AFAICT if I want to transfer bulk > messages using DMA, I can't just use kalloc and usb_bulk_msg, but need > usb_alloc_coherent, usb_fill_bulk_urb and usb_submit_urb, correct? > > Also, can you suggest any documentation regarding the relation between > videobuf2 and DMA? videobuf2 is a buffer management library for V4L2 drivers. It handles buffer allocation and freeing and offers a set of helpers to implement V4L2 ioctls. As such videobuf2 doesn't perform DMA operations, but it allocates buffers in a way that allows DMA (with several allocators depending on your hardware DMA requirements). -- Regards, Laurent Pinchart -- 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
