From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 44665C282CE for ; Tue, 9 Apr 2019 09:38:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 033422133D for ; Tue, 9 Apr 2019 09:38:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726880AbfDIJh6 (ORCPT ); Tue, 9 Apr 2019 05:37:58 -0400 Received: from lb1-smtp-cloud8.xs4all.net ([194.109.24.21]:47828 "EHLO lb1-smtp-cloud8.xs4all.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726387AbfDIJh6 (ORCPT ); Tue, 9 Apr 2019 05:37:58 -0400 Received: from [IPv6:2001:983:e9a7:1:21c4:edff:e18c:6e5e] ([IPv6:2001:983:e9a7:1:21c4:edff:e18c:6e5e]) by smtp-cloud8.xs4all.net with ESMTPA id DnCRhgmvKUjKfDnCShbx4r; Tue, 09 Apr 2019 11:37:54 +0200 Subject: Re: [PATCH v3 2/2] media: docs-rst: Document memory-to-memory video encoder interface To: Tomasz Figa Cc: Linux Media Mailing List , Linux Kernel Mailing List , Mauro Carvalho Chehab , Pawel Osciak , Alexandre Courbot , Kamil Debski , Andrzej Hajda , Kyungmin Park , Jeongtae Park , Philipp Zabel , =?UTF-8?B?VGlmZmFueSBMaW4gKOael+aFp+ePiik=?= , =?UTF-8?B?QW5kcmV3LUNUIENoZW4gKOmZs+aZuui/qik=?= , Stanimir Varbanov , Todor Tomov , Nicolas Dufresne , Paul Kocialkowski , Laurent Pinchart , dave.stevenson@raspberrypi.org, Ezequiel Garcia , Maxime Jourdan References: <20190124100419.26492-1-tfiga@chromium.org> <20190124100419.26492-3-tfiga@chromium.org> From: Hans Verkuil Message-ID: <2376896b-0087-5eee-a4b9-6ad03b0fef9c@xs4all.nl> Date: Tue, 9 Apr 2019 11:37:51 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-CMAE-Envelope: MS4wfJZZc4O1W+Xo6hsVnZgrrHojoZcHLyE3sjbmJ5sjOwiZcsghdk3h8binM4mv11wQT0c08n0Ed5XnYxs+yn9wFbgdv/j2zoHEblp53kGzE/of1nckUAed kI8Ry6Wb32WlPbZ4l80bILvk6KxvFN2U3SH2TX6hgv+XddSQ5TYCOC/XMdaU4gDrSuELfIanNvvYkr539wuzOvIWVcpTmHubxnY/2kGnviU7CjBVJIEftpGA OnTLMx4MausrWsqA40z1WgxzHU5nhDIpHCpePjn7ZW5elNM+eLJpw1A6LUq0jCdPvQUlsAS2qo7h535uNGaKajweJABiC63v+0Tht1uMPH7KU4Q23J94v7U4 EDTzrSDZKjS4pizjl6yw7Bcz8tXB3NzhM65D33xMCShkfLohrYLyDKG1ly0qTBoCtwvEXfrXIPKvslPcuA3mi9Ni4vkh7FwCuOKjUS9I0qWVKWChXs56eEmt UPyRYzQja+NHXYbLsJQ1Yhg04mhgvOrprruSHfrGeawDlgUEGBcr514l0pQMKNzqr/RkQpEpNo+nzze3dezkZlYVnRvWvS9o4iUfS/nrbP1SfJVfdeJ1cCbW dExklwBGvDg0arGRJmltPnQdfG7Ku8mHxhtj5R3eUuALgazZTUx/QiY1mZ6RT+xRd5NGFWbzZmBIlD1Tn87VHTciPtIMAW7Ux/iu5+7UtCSTDw6xE8PA5ohw uxRhGP0Lm6s2sVIibT5Wib2o0AEvi8LdH2iz5CQXmOUmOXCAaV5c9tTdNG2+QoMO2F7RsKSCrcPtF74u7280qUDbRyW143PKoJvEHJEpIm6Z2E4j/6BFUxDk 6iWDelXTA33ek7y11uVNXpTzRzJcKBWhXzJ5gA8lJlAsPv18csCnIVTybffd1d6EROMa870ugxxFWTdbfhlFSKoJDPkBzbsv8ZhdZGKBC5s7ByR4YvZ7kdDN +U4Pk7eD/Me9u/f3Bj+xy+mC7EA0D2pNfjioXtAfQXFWMn9Y Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org On 4/9/19 9:11 AM, Tomasz Figa wrote: > On Mon, Apr 8, 2019 at 5:43 PM Hans Verkuil wrote: >> >> On 4/8/19 10:36 AM, Tomasz Figa wrote: >>> On Mon, Mar 25, 2019 at 10:12 PM Hans Verkuil 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 > > * 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). 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 >>> >>