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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,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 ECCEAC282D9 for ; Thu, 31 Jan 2019 12:44:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CA4792086C for ; Thu, 31 Jan 2019 12:44:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733058AbfAaMoR (ORCPT ); Thu, 31 Jan 2019 07:44:17 -0500 Received: from metis.ext.pengutronix.de ([85.220.165.71]:55309 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727108AbfAaMoQ (ORCPT ); Thu, 31 Jan 2019 07:44:16 -0500 Received: from lupine.hi.pengutronix.de ([2001:67c:670:100:3ad5:47ff:feaf:1a17] helo=lupine) by metis.ext.pengutronix.de with esmtp (Exim 4.89) (envelope-from ) id 1gpBhV-0005db-2h; Thu, 31 Jan 2019 13:44:13 +0100 Message-ID: <1548938648.4585.3.camel@pengutronix.de> Subject: Re: [PATCH v3 1/2] media: docs-rst: Document memory-to-memory video decoder interface From: Philipp Zabel To: Hans Verkuil , Tomasz Figa , linux-media@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Mauro Carvalho Chehab , Pawel Osciak , Alexandre Courbot , Kamil Debski , Andrzej Hajda , Kyungmin Park , Jeongtae Park , Tiffany Lin =?UTF-8?Q?=28=E6=9E=97=E6=85=A7=E7=8F=8A=29?= , Andrew-CT Chen =?UTF-8?Q?=28=E9=99=B3=E6=99=BA=E8=BF=AA=29?= , Stanimir Varbanov , Todor Tomov , Nicolas Dufresne , Paul Kocialkowski , Laurent Pinchart , dave.stevenson@raspberrypi.org, Ezequiel Garcia , Maxime Jourdan Date: Thu, 31 Jan 2019 13:44:08 +0100 In-Reply-To: <54430438-33a3-2c52-b6c8-4000a4088906@xs4all.nl> References: <20190124100419.26492-1-tfiga@chromium.org> <20190124100419.26492-2-tfiga@chromium.org> <54430438-33a3-2c52-b6c8-4000a4088906@xs4all.nl> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.22.6-1+deb9u1 Mime-Version: 1.0 Content-Transfer-Encoding: 8bit X-SA-Exim-Connect-IP: 2001:67c:670:100:3ad5:47ff:feaf:1a17 X-SA-Exim-Mail-From: p.zabel@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2019-01-31 at 13:30 +0100, Hans Verkuil wrote: > On 1/31/19 11:45 AM, Hans Verkuil wrote: > > On 1/24/19 11:04 AM, Tomasz Figa wrote: > > > Due to complexity of the video decoding process, the V4L2 drivers of > > > stateful decoder hardware require specific sequences of V4L2 API calls > > > to be followed. These include capability enumeration, initialization, > > > decoding, seek, pause, dynamic resolution change, drain and end of > > > stream. > > > > > > Specifics of the above have been discussed during Media Workshops at > > > LinuxCon Europe 2012 in Barcelona and then later Embedded Linux > > > Conference Europe 2014 in Düsseldorf. The de facto Codec API that > > > originated at those events was later implemented by the drivers we already > > > have merged in mainline, such as s5p-mfc or coda. > > > > > > The only thing missing was the real specification included as a part of > > > Linux Media documentation. Fix it now and document the decoder part of > > > the Codec API. > > > > > > Signed-off-by: Tomasz Figa > > > --- > > > Documentation/media/uapi/v4l/dev-decoder.rst | 1076 +++++++++++++++++ > > > Documentation/media/uapi/v4l/dev-mem2mem.rst | 5 + > > > Documentation/media/uapi/v4l/pixfmt-v4l2.rst | 5 + > > > Documentation/media/uapi/v4l/v4l2.rst | 10 +- > > > .../media/uapi/v4l/vidioc-decoder-cmd.rst | 40 +- > > > Documentation/media/uapi/v4l/vidioc-g-fmt.rst | 14 + > > > 6 files changed, 1135 insertions(+), 15 deletions(-) > > > create mode 100644 Documentation/media/uapi/v4l/dev-decoder.rst > > > > > > > > > > > > +4. **This step only applies to coded formats that contain resolution information > > > + in the stream.** Continue queuing/dequeuing bitstream buffers to/from the > > > + ``OUTPUT`` queue via :c:func:`VIDIOC_QBUF` and :c:func:`VIDIOC_DQBUF`. The > > > + buffers will be processed and returned to the client in order, until > > > + required metadata to configure the ``CAPTURE`` queue are found. This is > > > + indicated by the decoder sending a ``V4L2_EVENT_SOURCE_CHANGE`` event with > > > + ``V4L2_EVENT_SRC_CH_RESOLUTION`` source change type. > > > + > > > + * It is not an error if the first buffer does not contain enough data for > > > + this to occur. Processing of the buffers will continue as long as more > > > + data is needed. > > > + > > > + * If data in a buffer that triggers the event is required to decode the > > > + first frame, it will not be returned to the client, until the > > > + initialization sequence completes and the frame is decoded. > > > + > > > + * If the client sets width and height of the ``OUTPUT`` format to 0, > > > + calling :c:func:`VIDIOC_G_FMT`, :c:func:`VIDIOC_S_FMT`, > > > + :c:func:`VIDIOC_TRY_FMT` or :c:func:`VIDIOC_REQBUFS` on the ``CAPTURE`` > > > + queue will return the ``-EACCES`` error code, until the decoder > > > + configures ``CAPTURE`` format according to stream metadata. > > > > I think this should also include the G/S_SELECTION ioctls, right? > > I've started work on adding compliance tests for codecs to v4l2-compliance and > I quickly discovered that this 'EACCES' error code is not nice at all. > > The problem is that it is really inconsistent with V4L2 behavior: the basic > rule is that there always is a format defined, i.e. G_FMT will always return > a format. > > Suddenly returning an error is actually quite painful to handle because it is > a weird exception just for the capture queue of a stateful decoder if no > output resolution is known. > > Just writing that sentence is painful. > > Why not just return some default driver defined format? It will automatically > be updated once the decoder parsed the bitstream and knows the new resolution. > > It really is just the same behavior as with a resolution change. > > It is also perfectly fine to request buffers for the capture queue for that > default format. It's pointless, but not a bug. > > Unless I am missing something I strongly recommend changing this behavior. I just wrote the same in my reply to Nicolas, the CODA driver currently sets the capture queue width/height to the output queue's crop rectangle (rounded to macroblock size) without ever having seen the SPS. regards Philipp