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@xxxxxxxxxxxxx>
> > ---
> > 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)
> >
