On Wed, 22 May 2019 17:43:49 +0900, Tomasz Figa wrote: > On Tue, Apr 9, 2019 at 6:43 PM Tomasz Figa <tf...@chromium.org> wrote: > > > > On Tue, Apr 9, 2019 at 6:37 PM Hans Verkuil <hverk...@xs4all.nl> wrote: > > > > > > On 4/9/19 9:11 AM, Tomasz Figa wrote: > > > > On Mon, Apr 8, 2019 at 5:43 PM Hans Verkuil <hverk...@xs4all.nl> wrote: > > > > > > > >> > > > >> On 4/8/19 10:36 AM, Tomasz Figa wrote: > > > >>> On Mon, Mar 25, 2019 at 10:12 PM Hans Verkuil <hverk...@xs4all.nl> > > > >>> wrote: > > > >>>> > > > >>>> Another comment found while creating compliance tests: > > > >>>> > > > >>>> On 1/24/19 11:04 AM, Tomasz Figa wrote: > > > >>>>> +Drain > > > >>>>> +===== > > > >>>>> + > > > >>>>> +To ensure that all the queued ``OUTPUT`` buffers have been > > > >>>>> processed and the > > > >>>>> +related ``CAPTURE`` buffers are given to the client, the client > > > >>>>> must follow the > > > >>>>> +drain sequence described below. After the drain sequence ends, the > > > >>>>> client has > > > >>>>> +received all encoded frames for all ``OUTPUT`` buffers queued > > > >>>>> before the > > > >>>>> +sequence was started. > > > >>>>> + > > > >>>>> +1. Begin the drain sequence by issuing > > > >>>>> :c:func:`VIDIOC_ENCODER_CMD`. > > > >>>>> + > > > >>>>> + * **Required fields:** > > > >>>>> + > > > >>>>> + ``cmd`` > > > >>>>> + set to ``V4L2_ENC_CMD_STOP`` > > > >>>>> + > > > >>>>> + ``flags`` > > > >>>>> + set to 0 > > > >>>>> + > > > >>>>> + ``pts`` > > > >>>>> + set to 0 > > > >>>>> + > > > >>>>> + .. warning:: > > > >>>>> + > > > >>>>> + The sequence can be only initiated if both ``OUTPUT`` and > > > >>>>> ``CAPTURE`` > > > >>>>> + queues are streaming. For compatibility reasons, the call to > > > >>>>> + :c:func:`VIDIOC_ENCODER_CMD` will not fail even if any of > > > >>>>> the queues is > > > >>>>> + not streaming, but at the same time it will not initiate the > > > >>>>> `Drain` > > > >>>>> + sequence and so the steps described below would not be > > > >>>>> applicable. > > > >>>>> + > > > >>>>> +2. Any ``OUTPUT`` buffers queued by the client before the > > > >>>>> + :c:func:`VIDIOC_ENCODER_CMD` was issued will be processed and > > > >>>>> encoded as > > > >>>>> + normal. The client must continue to handle both queues > > > >>>>> independently, > > > >>>>> + similarly to normal encode operation. This includes: > > > >>>>> + > > > >>>>> + * queuing and dequeuing ``CAPTURE`` buffers, until a buffer > > > >>>>> marked with the > > > >>>>> + ``V4L2_BUF_FLAG_LAST`` flag is dequeued, > > > >>>>> + > > > >>>>> + .. warning:: > > > >>>>> + > > > >>>>> + The last buffer may be empty (with :c:type:`v4l2_buffer` > > > >>>>> + ``bytesused`` = 0) and in that case it must be ignored by > > > >>>>> the client, > > > >>>>> + as it does not contain an encoded frame. > > > >>>>> + > > > >>>>> + .. note:: > > > >>>>> + > > > >>>>> + Any attempt to dequeue more buffers beyond the buffer > > > >>>>> marked with > > > >>>>> + ``V4L2_BUF_FLAG_LAST`` will result in a -EPIPE error from > > > >>>>> + :c:func:`VIDIOC_DQBUF`. > > > >>>>> + > > > >>>>> + * dequeuing processed ``OUTPUT`` buffers, until all the buffers > > > >>>>> queued > > > >>>>> + before the ``V4L2_ENC_CMD_STOP`` command are dequeued, > > > >>>>> + > > > >>>>> + * dequeuing the ``V4L2_EVENT_EOS`` event, if the client > > > >>>>> subscribes to it. > > > >>>>> + > > > >>>>> + .. note:: > > > >>>>> + > > > >>>>> + For backwards compatibility, the encoder will signal a > > > >>>>> ``V4L2_EVENT_EOS`` > > > >>>>> + event when the last frame has been decoded and all frames > > > >>>>> are ready to be > > > >>>>> + dequeued. It is deprecated behavior and the client must not > > > >>>>> rely on it. > > > >>>>> + The ``V4L2_BUF_FLAG_LAST`` buffer flag should be used > > > >>>>> instead. > > > >>>>> + > > > >>>>> +3. Once all ``OUTPUT`` buffers queued before the > > > >>>>> ``V4L2_ENC_CMD_STOP`` call are > > > >>>>> + dequeued and the last ``CAPTURE`` buffer is 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 not be reset and > > > >>>>> will resume > > > >>>>> + operation normally, with all the state from before the drain, > > > >>>>> > > > >>>> > > > >>>> I assume that calling CMD_START when *not* draining will succeed but > > > >>>> does nothing. > > > >>>> > > > >>>> In other words: while draining is in progress START will return > > > >>>> EBUSY. When draining > > > >>>> was finished, then START will resume the encoder. In all other cases > > > >>>> it just returns > > > >>>> 0 since the encoder is really already started. > > > >>>> > > > >>> > > > >>> Yes, that was the intention and seems to be the closest to the > > > >>> behavior described in the existing documentation. > > > >>> > > > >>>>> + > > > >>>>> + * a pair of :c:func:`VIDIOC_STREAMOFF` and > > > >>>>> :c:func:`VIDIOC_STREAMON` on the > > > >>>>> + ``CAPTURE`` queue - the encoder will be reset (see the > > > >>>>> `Reset` sequence) > > > >>>>> + and then resume encoding, > > > >>>>> + > > > >>>>> + * a pair of :c:func:`VIDIOC_STREAMOFF` and > > > >>>>> :c:func:`VIDIOC_STREAMON` on the > > > >>>>> + ``OUTPUT`` queue - the encoder will resume operation > > > >>>>> normally, however any > > > >>>>> + source frames queued to the ``OUTPUT`` queue between > > > >>>>> ``V4L2_ENC_CMD_STOP`` > > > >>>>> + and :c:func:`VIDIOC_STREAMOFF` will be discarded. > > > >>>>> + > > > >>>>> +.. note:: > > > >>>>> + > > > >>>>> + Once the drain sequence is initiated, the client needs to drive > > > >>>>> it to > > > >>>>> + completion, as described by the steps above, unless it aborts > > > >>>>> the process by > > > >>>>> + issuing :c:func:`VIDIOC_STREAMOFF` on any of the ``OUTPUT`` or > > > >>>>> ``CAPTURE`` > > > >>>>> + queues. The client is not allowed to issue > > > >>>>> ``V4L2_ENC_CMD_START`` or > > > >>>>> + ``V4L2_ENC_CMD_STOP`` again while the drain sequence is in > > > >>>>> progress and they > > > >>>>> + will fail with -EBUSY error code if attempted. > > > >>>> > > > >>>> I assume calling STOP again once the drain sequence completed just > > > >>>> returns 0 and > > > >>>> doesn't do anything else (since we're already stopped). > > > >>>> > > > >>> > > > >>> Right. > > > >>> > > > >>>>> + > > > >>>>> + Although mandatory, the availability of encoder commands may be > > > >>>>> queried > > > >>>>> + using :c:func:`VIDIOC_TRY_ENCODER_CMD`. > > > >>>> > > > >>>> Some corner cases: > > > >>>> > > > >>>> 1) No buffers are queued on either vb2_queue, but STREAMON is called > > > >>>> for both queues. > > > >>>> Now ENC_CMD_STOP is issued. What should happen? > > > >>>> > > > >>>> Proposal: the next time the applications queues a CAPTURE buffer > > > >>>> it is returned > > > >>>> at once as an empty buffer with FLAG_LAST set. > > > >>>> > > > >>> > > > >>> SGTM. It's actually similar to a relatively common case where all > > > >>> CAPTURE buffers have been dequeued and the application has to refill > > > >>> the CAPTURE queue, but in the meantime a drain request needs to be > > > >>> issued. > > > >>> > > > >>>> 2) Both queues are streaming and buffers have been encoded, but > > > >>>> currently no buffers > > > >>>> are queued on either vb2_queue. Now ENC_CMD_STOP is issued. What > > > >>>> should happen? > > > >>>> > > > >>>> Proposal: the next time the applications queues a CAPTURE buffer > > > >>>> it is returned > > > >>>> at once as an empty buffer with FLAG_LAST set. This is consistent > > > >>>> with the > > > >>>> previous corner case. > > > >>> > > > >>> Agreed. > > > >>> > > > >>>> > > > >>>> 3) The CAPTURE queue contains buffers, the OUTPUT queue does not. > > > >>>> Now ENC_CMD_STOP > > > >>>> is issued. What should happen? > > > >>>> > > > >>>> Proposal: the oldest CAPTURE buffer in the ready queue is > > > >>>> returned as an empty > > > >>>> buffer with FLAG_LAST set. > > > >>> > > > >>> Generally agreed, but not sure if there is a reason to specifically > > > >>> refer to the oldest buffer. (I'm personally for keeping the queues > > > >>> ordered, though...) > > > >> > > > >> Feel free to rephrase. Perhaps: "an empty CAPTURE buffer with > > > >> FLAG_LAST set should be > > > >> queued up for userspace to signal that the encoder has stopped." Or > > > >> something along > > > >> those lines. > > > > > > > > I've added a note: > > > > > > > > For reference, handling of various corner cases is described below: > > > > > > > > * In case of no buffer in the ``OUTPUT`` queue at the time the > > > > ``V4L2_ENC_CMD_STOP`` command was issued, the drain sequence > > > > completes > > > > immediately and the encoder returns an empty ``CAPTURE`` buffer > > > > with the > > > > ``V4L2_BUF_FLAG_LAST`` flag set. > > > > > > > > * In case of no buffer in the ``CAPTURE`` queue at the time the drain > > > > sequence completes, the next time the client queues a ``CAPTURE`` > > > > buffer > > > > it is returned at once as an empty buffer with the > > > > ``V4L2_BUF_FLAG_LAST`` > > > > flag set. > > > > > > > > * If :c:func:`VIDIOC_STREAMOFF` is called on the ``CAPTURE`` queue > > > > in the > > > > middle of the drain sequence, the drain sequence is cancelled and > > > > all > > > > > > cancelled -> canceled > > > > > > > ``CAPTURE`` buffers are implicitly returned to the userpace. > > > > > > userpace -> userspace > > > > > > > Actually changed it to "client". > > > > > > > > > > * If :c:func:`VIDIOC_STREAMOFF` is called on the ``OUTPUT`` queue in > > > > the > > > > middle of the drain sequence, the drain sequence completes > > > > immediately and > > > > next ``CAPTURE`` buffer will be returned empty with the > > > > ``V4L2_BUF_FLAG_LAST`` flag set. > > > > > > > > Slightly changed the split into cases to cover behaviors rather than > > > > conditions. WDYT? > > > > > > Looks good (with those two typos fixed). > > > > > > > Thanks. > > Hmm, we actually looked into implementing this in mtk-vcodec and > handling of this corner case gets quite complicated. When stopping the > streaming on OUTPUT, you may not have any available CAPTURE buffer, so > you need to keep some extra state in the driver and check it in vb2 > .buf_queue for CAPTURE to return the first buffer and complete the > drain. > > The general handling of drain would have to look like this: > - VIDIOC_DECODER_CMD must check if a drain isn't already in progress > and also whether the queues are streaming, > - STREAMOFF(CAPTURE) needs to cancel any pending drain, > - STREAMOFF(OUTPUT) needs to return a CAPTURE buffer with LAST set if > there is one or postpone it until a buffer is queued, > - QBUF(CAPTURE) must return the buffer instantly if such return was > postponed by STREAMOFF(OUTPUT). > - DQBUF(CAPTURE) of a buffer with the LAST flag set would finish the > sequence. > > Sounds like we definitely need some generic code to handle this...
I implemented this as well for allegro. I ended up exactly with an additional state (ALLEGRO_STATE_WAIT_FOR_BUFFER) to handle this corner case. The implementation was tricky and I would highly appreciate generic code that is used by other drivers as well. Michael > > > > > > Hans > > > > > > > > > > > Best regards, > > > > Tomasz > > > > . > > > >> > > > >> Regards, > > > >> > > > >> Hans > > > >> > > > >>> > > > >>>> > > > >>>> 4) Both queues have queued buffers. ENC_CMD_STOP is issued to start > > > >>>> the drain process. > > > >>>> Before the drain process completes STREAMOFF is called for either > > > >>>> CAPTURE or > > > >>>> OUTPUT queue. What should happen? > > > >>>> > > > >>>> Proposal for STREAMOFF(CAPTURE): aborts the drain process and all > > > >>>> CAPTURE buffers are > > > >>>> returned to userspace. If encoding is restarted, then any > > > >>>> remaining OUTPUT buffers > > > >>>> will be used as input to the encoder. > > > >>>> > > > >>> > > > >>> Agreed. > > > >>> > > > >>>> Proposal for STREAMOFF(OUTPUT): the next capture buffer will be > > > >>>> empty and have > > > >>>> FLAG_LAST set. > > > >>> > > > >>> Agreed. > > > >>> > > > >>>> > > > >>>> Some of this might have to be documented, but these corner cases > > > >>>> should certainly be > > > >>>> tested by v4l2-compliance. Before I write those tests I'd like to > > > >>>> know if you agree > > > >>>> with this. > > > >>> > > > >>> Agreed with just one minor comment. Thanks for checking with me! > > > >>> > > > >>> Best regards, > > > >>> Tomasz > > > >>> > > > >> > > > >
