linux-kernel - Re: [PATCH v3 0/2] Document memory-to-memory video codec interfaces

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Date:   Thu, 24 Jan 2019 11:38:04 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Tomasz Figa <tfiga@...omium.org>, linux-media@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Pawel Osciak <posciak@...omium.org>,
        Alexandre Courbot <acourbot@...omium.org>,
        Kamil Debski <kamil@...as.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Jeongtae Park <jtp.park@...sung.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Tiffany Lin (林慧珊) 
        <tiffany.lin@...iatek.com>,
        Andrew-CT Chen (陳智迪) 
        <andrew-ct.chen@...iatek.com>,
        Stanimir Varbanov <stanimir.varbanov@...aro.org>,
        Todor Tomov <todor.tomov@...aro.org>,
        Nicolas Dufresne <nicolas@...fresne.ca>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        dave.stevenson@...pberrypi.org,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Maxime Jourdan <maxi.jourdan@...adoo.fr>
Subject: Re: [PATCH v3 0/2] Document memory-to-memory video codec interfaces

On 01/24/19 11:04, Tomasz Figa wrote:
> Late happy new year everyone. It's been a while, but here is the v3 of
> the stateful mem2mem codec interfaces documentation. Sorry for taking so
> long time to respin. (Again.)
> 
> This series attempts to add the documentation of what was discussed
> during Media Workshops at LinuxCon Europe 2012 in Barcelona and then
> later Embedded Linux Conference Europe 2014 in Düsseldorf and then
> eventually written down by Pawel Osciak and tweaked a bit by Chrome OS
> video team (but mostly in a cosmetic way or making the document more
> precise), during the several years of Chrome OS using the APIs in
> production.
> 
> Note that most, if not all, of the API is already implemented in
> existing mainline drivers, such as s5p-mfc or mtk-vcodec. Intention of
> this series is just to formalize what we already have.
> 
> Thanks everyone for the huge amount of useful comments for the RFC and
> v1. Much of the credits should go to Pawel Osciak too, for writing most
> of the original text of the initial RFC.

Thank you very much for this v3.

I've updated the spec with this v3 + Alexandre's v2 incorporated here:

https://hverkuil.home.xs4all.nl/codec-api/uapi/v4l/dev-mem2mem.html

I plan to review this as soon as I can because I really would like to
get this merged for 5.1.

Regards,

	Hans

> 
> Changes since v2:
> (https://lore.kernel.org/patchwork/cover/1002474/)
> Decoder:
>  - Specified that the initial source change event is signaled
>    regardless of whether the client-set format matches the
>    stream format.
>  - Dropped V4L2_CID_MIN_BUFFERS_FOR_OUTPUT since it's meaningless
>    for the bitstream input buffers of decoders.
>  - Explicitly stated that VIDIOC_REQBUFS is not allowed on CAPTURE
>    if the stream information is not available.
>  - Described decode error handling.
>  - Mentioned that timestamps can be observed after a seek to
>    determine whether the CAPTURE buffers originated from before
>    or after the seek.
>  - Explicitly stated that after a pair of V4L2_DEC_CMD_STOP and
>    V4L2_DEC_CMD_START, the decoder is not reset and preserves
>    all the state.
> 
> Encoder:
>  - Specified that width and height of CAPTURE format are ignored
>    and always zero.
>  - Explicitly noted the common use case for the CROP target with
>    macroblock-unaligned video resolutions.
>  - Added a reference to Request API.
>  - Dropped V4L2_CID_MIN_BUFFERS_FOR_CAPTURE since it's meaningless
>    for the bitstream output buffers of encoders.
>  - Explicitly stated that after a pair of V4L2_ENC_CMD_STOP and
>    V4L2_ENC_CMD_START, the encoder is not reset and preserves
>    all the state.
> 
> General:
>  - Dropped format enumeration from "Initialization", since it's already
>    a part of "Querying capabilities".
>  - Many spelling, grammar, stylistic, etc. changes.
>  - Changed the style of note blocks.
>  - Rebased onto Hans' documentation cleanup series.
>    (https://patchwork.kernel.org/cover/10775407/
>     https://patchwork.kernel.org/patch/10776737/)
>  - Moved the interfaces under the "Video Memory-To-Memory Interface"
>    section.
> 
> For changes since v1 see the v2:
> https://lore.kernel.org/patchwork/cover/1002474/
> 
> For changes since RFC see the v1:
> https://patchwork.kernel.org/cover/10542207/
> 
> Tomasz Figa (2):
>   media: docs-rst: Document memory-to-memory video decoder interface
>   media: docs-rst: Document memory-to-memory video encoder interface
> 
>  Documentation/media/uapi/v4l/dev-decoder.rst  | 1076 +++++++++++++++++
>  Documentation/media/uapi/v4l/dev-encoder.rst  |  586 +++++++++
>  Documentation/media/uapi/v4l/dev-mem2mem.rst  |    6 +
>  Documentation/media/uapi/v4l/pixfmt-v4l2.rst  |   10 +
>  Documentation/media/uapi/v4l/v4l2.rst         |   12 +-
>  .../media/uapi/v4l/vidioc-decoder-cmd.rst     |   40 +-
>  .../media/uapi/v4l/vidioc-encoder-cmd.rst     |   38 +-
>  Documentation/media/uapi/v4l/vidioc-g-fmt.rst |   14 +
>  8 files changed, 1752 insertions(+), 30 deletions(-)
>  create mode 100644 Documentation/media/uapi/v4l/dev-decoder.rst
>  create mode 100644 Documentation/media/uapi/v4l/dev-encoder.rst
>