linux-kernel - Re: Re: Re: [PATCH v3 09/14] media: uapi: Add V4L2_CID_STATELESS_HEVC_ENTRY_POINT

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Message-ID: <7348885.EvYhyI6sBW@kista>
Date:   Sat, 26 Feb 2022 19:17:46 +0100
From:   Jernej Škrabec <jernej.skrabec@...il.com>
To:     mchehab@...nel.org, ezequiel@...guardiasur.com.ar,
        p.zabel@...gutronix.de, gregkh@...uxfoundation.org,
        mripard@...nel.org, paul.kocialkowski@...tlin.com, wens@...e.org,
        jonas@...boo.se, nicolas@...fresne.ca,
        Benjamin Gaignard <benjamin.gaignard@...labora.com>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-staging@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        kernel@...labora.com, knaerzche@...il.com, jc@...esim.co.uk,
        Benjamin Gaignard <benjamin.gaignard@...labora.com>
Subject: Re: Re: Re: [PATCH v3 09/14] media: uapi: Add V4L2_CID_STATELESS_HEVC_ENTRY_POINT_OFFSET control

Dne sobota, 26. februar 2022 ob 18:59:18 CET je Jernej Škrabec napisal(a):
> Hi!
> 
> Dne petek, 25. februar 2022 ob 20:30:20 CET je Jernej Škrabec napisal(a):
> > Hi!
> > 
> > Dne petek, 25. februar 2022 ob 17:45:55 CET je Benjamin Gaignard 
napisal(a):
> > > The number of 'entry point offset' could be very variable.
> > > Rather than use a large static array define a v4l2 dynamic array
> > > of integer control.
> > 
> > I suggest we should be more specific and say U32 (V4L2_CTRL_TYPE_U32).
> > 
> > > The number of entry point offsets is reported by the elems field.
> 
> I did few more tests and these are my findings:
> 1. dynamic array can't be set over size, specified in .dims array
> 2. entry point offsets are per slice, so if we make slices dynamic array, 
then 
> entry points would become two dimensional dynamic array
> 3. num_entry_point_offsets must be part of slice control, because it can be 
> zero, but size of array can't be

Clarification: num_entry_point_offsets is needed in any case, even without entry 
point list.

> 4. fortunately, not setting entry points doesn't impact decoding 
correctness. 
> This is in line what John told me about them.
> 
> Hans, can you comment points 1-3? I might misunderstand point 1.
> 
> In short, it seems like we don't really need entry points, even if they are 
> used in BSP library. In both cases, I got fluster score 119/138 (10-bit 
> excluded), so we can just drop this patch, although I'm a bit uneasy not 
> setting entry points...
> 
> Best regards,
> Jernej
> 
> > > 
> > > Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
> > > ---
> > >  .../userspace-api/media/v4l/ext-ctrls-codec.rst          | 9 +++++++++
> > >  include/media/hevc-ctrls.h                               | 1 +
> > >  2 files changed, 10 insertions(+)
> > > 
> > > diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/
> > Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> > > index 44a268a948c0..71f7dc1c1ccd 100644
> > > --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> > > +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> > > @@ -3128,6 +3128,15 @@ enum v4l2_mpeg_video_hevc_size_of_length_field -
> > >  
> > >      \normalsize
> > >  
> > > +``V4L2_CID_STATELESS_HEVC_ENTRY_POINT_OFFSETS (integer)``
> > 
> > Here you have OFFSETS (plural) ...
> > 
> > > +    Specifies the i-th entry point offset in bytes and is represented by
> > > +    offset_len_minus1 plus 1 bits.
> > 
> > You probably mean entry_point_offset_minus1? offset_len_minus1 just tells 
how 
> > much bits need to be read for each element and it's not important for 
actual 
> > decoding.
> > 
> > > +    This control is a dynamically sized array. The number of entry 
point
> > > +    offsets is reported by the ``elems`` field.
> > > +    This bitstream parameter is defined according to :ref:`hevc`.
> > > +    They are described in section 7.4.7.1 "General slice segment header
> > > +    semantics" of the specification.
> > > +
> > >  ``V4L2_CID_STATELESS_HEVC_SCALING_MATRIX (struct)``
> > >      Specifies the HEVC scaling matrix parameters used for the scaling 
> > process
> > >      for transform coefficients.
> > > diff --git a/include/media/hevc-ctrls.h b/include/media/hevc-ctrls.h
> > > index 3016c1abb1d0..3f8a67924df3 100644
> > > --- a/include/media/hevc-ctrls.h
> > > +++ b/include/media/hevc-ctrls.h
> > > @@ -20,6 +20,7 @@
> > >  #define V4L2_CID_STATELESS_HEVC_DECODE_PARAMS	(V4L2_CID_CODEC_BASE + 
> > 1012)
> > >  #define V4L2_CID_STATELESS_HEVC_DECODE_MODE	(V4L2_CID_CODEC_BASE + 
> > 1015)
> > >  #define V4L2_CID_STATELESS_HEVC_START_CODE	(V4L2_CID_CODEC_BASE 
+ 
> 1016)
> > > +#define V4L2_CID_STATELESS_HEVC_ENTRY_POINT_OFFSET (V4L2_CID_CODEC_BASE 
+ 
> > 1017)
> > 
> > ... and here you have OFFSET (singlular). I suggest plural form to be used 
> in 
> > all places, including subject line of this commit.
> > 
> > Additionally, it would be nice if control is initialized, like so:
> > https://github.com/jernejsk/linux-1/commit/
> > f938e162cd8dd77c9f6f1b248d80144840a37bce
> > 
> > Best regards,
> > Jernej
> > 
> > >  
> > >  /* enum v4l2_ctrl_type type values */
> > >  #define V4L2_CTRL_TYPE_HEVC_SPS 0x0120
> > > -- 
> > > 2.32.0
> > > 
> > > 
> > 
> > 
> > 
> 
> 
>