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    SubjectRe: [PATCH 0/2] Document memory-to-memory video codec interfaces
    Hi Philipp,

    On Wed, Jul 25, 2018 at 10:28 PM Philipp Zabel <p.zabel@pengutronix.de> wrote:
    >
    > Hi Tomasz,
    >
    > On Tue, 2018-07-24 at 23:06 +0900, Tomasz Figa wrote:
    > > 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.
    > >
    > > It is an initial conversion from Google Docs to RST, so formatting is
    > > likely to need some further polishing. It is also the first time for me
    > > to create such long RST documention. I could not find any other instance
    > > of similar userspace sequence specifications among our Media documents,
    > > so I mostly followed what was there in the source. Feel free to suggest
    > > a better format.
    > >
    > > Much of credits should go to Pawel Osciak, for writing most of the
    > > original text of the initial RFC.
    > >
    > > Changes since RFC:
    > > (https://lore.kernel.org/patchwork/project/lkml/list/?series=348588)
    > > - The number of changes is too big to list them all here. Thanks to
    > > a huge number of very useful comments from everyone (Philipp, Hans,
    > > Nicolas, Dave, Stanimir, Alexandre) we should have the interfaces much
    > > more specified now. The issues collected since previous revisions and
    > > answers leading to this revision are listed below.
    >
    > Thanks a lot for the update, and especially for the nice Q&A summary of
    > the discussions so far.
    >
    > [...]
    > > Decoder issues
    > >
    > [...]
    > > How should ENUM_FRAMESIZES be affected by profiles and levels?
    > >
    > > Answer: Not in current specification - the logic is too complicated and
    > > it might make more sense to actually handle this in user space. (In
    > > theory, level implies supported frame sizes + other factors.)
    >
    > For decoding I think it makes more sense to let the hardware decode them
    > from the stream and present them as read-only controls, such as:
    >
    > 42a68012e67c ("media: coda: add read-only h.264 decoder profile/level
    > controls")

    To clarify, this point is only about the effect on ENUM_FRAMESIZES.
    Profile and level controls are mentioned in capabilities enumeration,
    but it may make sense to add optional steps of querying them in
    Initialization sequence.

    >
    > if possible. For encoding, the coda firmware determines level from
    > bitrate and coded resolution, itself, so I agree not making this part of
    > the spec is a good idea for now.

    Encoder controls are driver-specific in general, since the encoding
    capabilities vary a lot, so I decided to just briefly mention the
    general idea of encoding parameters in "Encoding parameter changes"
    section. It could be a good idea to add a reference to the MPEG
    control documentation there, though.

    Best regards,
    Tomasz

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