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    SubjectRe: [PATCH v2 1/2] media: docs-rst: Document memory-to-memory video decoder interface
    On Wed, Jan 23, 2019 at 2:27 PM Tomasz Figa <tfiga@chromium.org> wrote:
    >
    > On Tue, Jan 22, 2019 at 11:47 PM Hans Verkuil <hverkuil@xs4all.nl> wrote:
    > >
    > > On 01/22/19 11:02, Tomasz Figa wrote:
    [snip]
    > > >>> + one ``CAPTURE`` buffer, the following cases are defined:
    > > >>> +
    > > >>> + * one ``OUTPUT`` buffer generates multiple ``CAPTURE`` buffers: the same
    > > >>> + ``OUTPUT`` timestamp will be copied to multiple ``CAPTURE`` buffers,
    > > >>> +
    > > >>> + * multiple ``OUTPUT`` buffers generate one ``CAPTURE`` buffer: timestamp of
    > > >>> + the ``OUTPUT`` buffer queued last will be copied,
    > > >>> +
    > > >>> + * the decoding order differs from the display order (i.e. the
    > > >>> + ``CAPTURE`` buffers are out-of-order compared to the ``OUTPUT`` buffers):
    > > >>> + ``CAPTURE`` timestamps will not retain the order of ``OUTPUT`` timestamps
    > > >>> + and thus monotonicity of the timestamps cannot be guaranteed.
    > >
    > > I think this last point should be rewritten. The timestamp is just a value that
    > > is copied, there are no monotonicity requirements for m2m devices in general.
    > >
    >
    > Actually I just realized the last point might not even be achievable
    > for some of the decoders (s5p-mfc, mtk-vcodec), as they don't report
    > which frame originates from which bitstream buffer and the driver just
    > picks the most recently consumed OUTPUT buffer to copy the timestamp
    > from. (s5p-mfc actually "forgets" to set the timestamp in some cases
    > too...)
    >
    > I need to think a bit more about this.

    Actually I misread the code. Both s5p-mfc and mtk-vcodec seem to
    correctly match the buffers.

    Best regards,
    Tomasz

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