Hi Laurent, Am Dienstag, den 03.02.2015, 13:20 +0200 schrieb Laurent Pinchart: > On Monday 02 February 2015 15:00:51 Hans Verkuil wrote: > > On 01/22/2015 12:28 PM, Philipp Zabel wrote: > > > If the last buffer was dequeued from a capture queue, let poll return > > > immediately and let DQBUF return -EPIPE to signal there will no more > > > buffers to dequeue until STREAMOFF. > > > > This looks OK to me, although I would like to see comments from others as > > well. Of course, this needs to be documented in the spec as well. > > I haven't followed the V4L2 codec API discussion during ELC-E. Could someone > briefly expose the rationale for this and the codec draining flow ? The > explanation should probably included in the documentation. This is the draining flow as written down in the notes: The decoder draining flow starts with the application making the driver aware of its intentions by calling VIDIOC_DECODER_CMD with V4L2_DEC_CMD_STOP. The driver processes the remaining buffers on the OUTPUT queue. Once all CAPTURE buffers produced from those are ready to dequeue, it sends a V4L2_EVENT_EOS. The application then dequeues buffers from the CAPTURE queue until it encounters a buffer with V4L2_BUF_FLAG_LAST set. This buffer may already be empty due to hardware limitations. Alternatively, the application may simply continue to dequeue (possibly empty) buffers until the VIDIOC_DQBUF ioctl returns -EPIPE. To resume decoding, the application can call VIDIOC_DECODER_CMD with V4L2_CMD_START without the need to stop streaming. This should work the same for encoding. The rationale for using -EPIPE was IIRC that it allows for simpler code (DQBUF loop until error). Also it works without the newest kernel headers that #define V4L2_BUF_FLAG_LAST. I don't remember if we talked about what should happen to new buffers queued via QBUF on the OUTPUT queue while in draining mode, but I suppose the driver should just hold them until V4L2_CMD_START is called. > Existing applications will receive -EPIPE from DQBUF now. Have potential > breakages been taken into account ? We can continue to produce empty frames this way, which are currently used to signal the last frame in s5p-mfc. I am not aware of other unspecified mechanisms in use. regards Philipp -- 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
