On 01/23/19 11:00, Tomasz Figa wrote: > On Sat, Nov 17, 2018 at 8:37 PM Hans Verkuil <hverkuil@xxxxxxxxx> wrote: >> >> On 11/17/2018 05:18 AM, Nicolas Dufresne wrote: >>> Le lundi 12 novembre 2018 à 14:23 +0100, Hans Verkuil a écrit : >>>> On 10/22/2018 04:49 PM, Tomasz Figa wrote: > [snip] >>>>> + rely on it. The ``V4L2_BUF_FLAG_LAST`` buffer flag should be used >>>>> + instead. >>>> >>>> Question: should new codec drivers still implement the EOS event? >>> >>> I'm been asking around, but I think here is a good place. Do we really >>> need the FLAG_LAST in userspace ? Userspace can also wait for the first >>> EPIPE return from DQBUF. >> >> I'm interested in hearing Tomasz' opinion. This flag is used already, so there >> definitely is a backwards compatibility issue here. >> > > FWIW, it would add the overhead of 1 more system call, although I > don't think it's of our concern. > > My personal feeling is that using error codes for signaling normal > conditions isn't very elegant, though. I agree. Let's keep this flag. Regards, Hans > >>> >>>> >>>>> + >>>>> +3. Once all ``OUTPUT`` buffers queued before the ``V4L2_ENC_CMD_STOP`` call and >>>>> + the last ``CAPTURE`` buffer are dequeued, the encoder is stopped and it will >>>>> + accept, but not process any newly queued ``OUTPUT`` buffers until the client >>>>> + issues any of the following operations: >>>>> + >>>>> + * ``V4L2_ENC_CMD_START`` - the encoder will resume operation normally, >>>> >>>> Perhaps mention that this does not reset the encoder? It's not immediately clear >>>> when reading this. >>> >>> Which drivers supports this ? I believe I tried with Exynos in the >>> past, and that didn't work. How do we know if a driver supports this or >>> not. Do we make it mandatory ? When it's not supported, it basically >>> mean userspace need to cache and resend the header in userspace, and >>> also need to skip to some sync point. >> >> Once we agree on the spec, then the next step will be to add good compliance >> checks and update drivers that fail the tests. >> >> To check if the driver support this ioctl you can call VIDIOC_TRY_ENCODER_CMD >> to see if the functionality is supported. > > There is nothing here for the hardware to support. It's an entirely > driver thing, since it just needs to wait for the encoder to complete > all the pending frames and stop enqueuing more frames to the decoder > until V4L2_ENC_CMD_START is called. Any driver that can't do it must > be fixed, since otherwise you have no way to ensure that you got all > the encoded output. > > Best regards, > Tomasz >
