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    SubjectRe: [PATCH 02/10] media: uapi: h264: Further clarify scaling lists order
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    On Thu, 2020-07-16 at 09:23 +0200, Hans Verkuil wrote:
    > On 15/07/2020 22:22, Ezequiel Garcia wrote:
    > > Commit 0b0393d59eb4a ("media: uapi: h264: clarify
    > > expected scaling_list_4x4/8x8 order") improved the
    > > documentation on H264 scaling lists order.
    > >
    > > This commit improves the documentation by clarifying
    > > that the lists themselves are expected in matrix order.
    >
    > "matrix order" is not a well defined term. Especially since different
    > programming languages lay out matrices differently (e.g. fortran uses
    > column-major order). Perhaps something like this is more unambiguous:
    >

    Agreed, "matrix order" is perhaps not a proper choice of words.

    > "The values on each scaling list are in row-major order."
    >
    > BTW, why not be explicit and use:
    >
    > __u8 scaling_list_4x4[6][4][4];
    > __u8 scaling_list_8x8[6][8][8];
    >
    > That makes it explicit and the order is just that of what the C language
    > uses.
    >

    I am not sure if that'll go in clearer direction.

    I'm thinking we just need to clarify the coefficients
    are in raster scan order, as opposed to a zig-zag scan
    order, which is a part of the decoding process.

    How about we simply say "raster scan order" and keep the patch as is?

    Thanks,
    Ezequiel


    > Regards,
    >
    > Hans
    >
    > > Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
    > > ---
    > > Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst | 6 ++++--
    > > 1 file changed, 4 insertions(+), 2 deletions(-)
    > >
    > > diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
    > > index c2e17c02f77e..16bfc98ab2f6 100644
    > > --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
    > > +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
    > > @@ -1725,12 +1725,14 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
    > > - ``scaling_list_4x4[6][16]``
    > > - Scaling matrix after applying the inverse scanning process.
    > > Expected list order is Intra Y, Intra Cb, Intra Cr, Inter Y,
    > > - Inter Cb, Inter Cr.
    > > + Inter Cb, Inter Cr. The values on each scaling list are
    > > + expected in matrix order.
    > > * - __u8
    > > - ``scaling_list_8x8[6][64]``
    > > - Scaling matrix after applying the inverse scanning process.
    > > Expected list order is Intra Y, Inter Y, Intra Cb, Inter Cb,
    > > - Intra Cr, Inter Cr.
    > > + Intra Cr, Inter Cr. The values on each scaling list are
    > > + expected in matrix order.
    > >
    > > ``V4L2_CID_MPEG_VIDEO_H264_SLICE_PARAMS (struct)``
    > > Specifies the slice parameters (as extracted from the bitstream)
    > >


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