Hi Bhupesh, On Thursday 26 April 2012 13:23:59 Bhupesh SHARMA wrote: > Hi Laurent, > > Sorry to jump-in before your reply on my previous mail, > but as I was studying the USERPTR stuff in more detail, I have a few more > queries which I believe you can include in your reply as well.. [snip] > I am now a bit confused on how the entire system will work now: > - Does USERPTR method needs to be supported both in UVC gadget and > soc-camera side, or one can still support the MMAP method and the other can > now be changed to support USERPTR method and we can achieve a ZERO buffer > copy operation using this method? You need USERPTR support on one side only. In practice many (all?) soc-camera drivers require physically contiguous memory, so you will need to use MMAP on the soc-camera side and USERPTR on the UVC gadget side. DMABUF, when merged in the kernel, will be a better solution (but will require all drivers to use vb2). > - More specifically, I would like to keep the soc-camera still using MMAP > (and hence still using video-buf) and make changes at the UVC gadget side > to support USERPTR and videobuf2. Will this work? Please see above :-) > - At the application side how should we design the flow in case both > support USERPTR, i.e. the buffer needs to be protected from simultaneous > access from the UVC gadget driver and soc-camera driver (to ensure that a > single buffer can be shared across them). Also in case we keep soc-camera > still using MMAP and UVC gadget side supporting USERPTR, how can we share a > common buffer across the UVC gadget and soc-camera driver. That's easy. Request the same number of buffers on both sides with REQBUFS, mmap() them to userspace on the soc-camera side, and then use the user pointer to queue them with QBUF on the UVC side. You just need to ensure that a buffer is never enqueued to two drivers at the same time. Wait for buffers to be ready on both sides with select(), and when a buffer is ready dequeue it and requeue it on the other side. > - In case of USERPTR method the camera capture hardware should be able to > DMA the received data to the user space buffers. Are there any specific > requirements on the DMA capability of these use-space buffers > (scatter-gather or contiguous?). DMA to userspace is quite hackish. You should use the MMAP method on the soc- camera side. -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
