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Date: Fri, 16 Aug 2019 09:29:13 -0300
From: Ezequiel Garcia <ezequiel@...labora.com>
To: Hans Verkuil <hverkuil@...all.nl>, linux-media@...r.kernel.org
Cc: kernel@...labora.com,
Nicolas Dufresne <nicolas.dufresne@...labora.com>,
Tomasz Figa <tfiga@...omium.org>,
linux-rockchip@...ts.infradead.org,
Heiko Stuebner <heiko@...ech.de>,
Jonas Karlman <jonas@...boo.se>,
Philipp Zabel <p.zabel@...gutronix.de>,
Boris Brezillon <boris.brezillon@...labora.com>,
Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
Alexandre Courbot <acourbot@...omium.org>,
fbuergisser@...omium.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 03/11] media: uapi: h264: Add the concept of decoding
mode
On Fri, 2019-08-16 at 09:34 +0200, Hans Verkuil wrote:
> On 8/14/19 9:59 PM, Ezequiel Garcia wrote:
> > From: Boris Brezillon <boris.brezillon@...labora.com>
> >
> > Some stateless decoders don't support per-slice decoding granularity
> > (or at least not in a way that would make them efficient or easy to use).
> >
> > Expose a menu to control the supported decoding modes. Drivers are
> > allowed to support only one decoding but they can support both too.
>
> The commit message doesn't say anything about the start_byte_offset
> addition and the num_slices documentation improvement. It probably
> should.
>
Yes, of course.
> See more comments below:
>
> > Signed-off-by: Boris Brezillon <boris.brezillon@...labora.com>
> > Reviewed-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> > Tested-by: Philipp Zabel <p.zabel@...gutronix.de>
> > ---
> > Changes in v6:
> > * Fix spec, specifiying the decode-mode pixelformat modifier
> > needs to be set once, as suggested by Hans.
> > * Rename, as suggested by Paul.
> > Changes in v5:
> > * Improve specification as suggested by Hans.
> > Changes in v4:
> > * Typos/rewording fixes
> > Changes in v3:
> > * s/per-{slice,frame} decoding/{slice,frame}-based decoding/
> > * Add Paul's R-b
> > Changes in v2:
> > * Allow decoding multiple slices in per-slice decoding mode
> > * Minor doc improvement/fixes
> > ---
> > .../media/uapi/v4l/ext-ctrls-codec.rst | 47 ++++++++++++++++++-
> > .../media/uapi/v4l/pixfmt-compressed.rst | 6 ++-
> > drivers/media/v4l2-core/v4l2-ctrls.c | 9 ++++
> > include/media/h264-ctrls.h | 10 ++++
> > 4 files changed, 69 insertions(+), 3 deletions(-)
> >
> > diff --git a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> > index c5f39dd50043..623b34f61b32 100644
> > --- a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> > +++ b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> > @@ -1747,6 +1747,11 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
> > * - __u32
> > - ``size``
> > -
> > + * - __u32
> > + - ``start_byte_offset``
> > + Offset (in bytes) from the beginning of the OUTPUT buffer to the start
> > + of the slice. If the slice starts with a start code, then this is the
> > + offset to such start code.
>
> This should mention that it should be set to 0 for SLICE_BASED decoding mode.
>
Right.
> > * - __u32
> > - ``header_bit_size``
> > -
> > @@ -1930,7 +1935,10 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
> > -
> > * - __u16
> > - ``num_slices``
> > - - Number of slices needed to decode the current frame
> > + - Number of slices needed to decode the current frame/field. When
> > + operating in slice-based decoding mode (see
> > + :c:type:`v4l2_mpeg_video_h264_decode_mode`), this field
> > + should always be set to one.
> > * - __u16
> > - ``nal_ref_idc``
> > - NAL reference ID value coming from the NAL Unit header
> > @@ -2021,6 +2029,43 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
> > - 0x00000004
> > - The DPB entry is a long term reference frame
> >
> > +``V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE (enum)``
> > + Specifies the decoding mode to use. Currently exposes slice-based and
> > + frame-based decoding but new modes might be added later on.
> > + This control is used as a modifier for V4L2_PIX_FMT_H264_SLICE
> > + pixel format. Applications that support V4L2_PIX_FMT_H264_SLICE
> > + are required to set this control in order to specify the decoding mode
> > + that is expected for the buffer.
> > + Drivers may expose a single or multiple decoding modes, depending
> > + on what they can support.
> > +
> > + .. note::
> > +
> > + This menu control is not yet part of the public kernel API and
> > + it is expected to change.
> > +
> > +.. c:type:: v4l2_mpeg_video_h264_decode_mode
> > +
> > +.. cssclass:: longtable
> > +
> > +.. flat-table::
> > + :header-rows: 0
> > + :stub-columns: 0
> > + :widths: 1 1 2
> > +
> > + * - ``V4L2_MPEG_VIDEO_H264_DECODE_MODE_SLICE_BASED``
> > + - 0
> > + - Decoding is done at the slice granularity.
> > + v4l2_ctrl_h264_decode_params->num_slices should be set to 1.
>
> And start_byte_offset should be set to 0.
>
OK.
> > + The OUTPUT buffer must contain a single slice.
> > + * - ``V4L2_MPEG_VIDEO_H264_DECODE_MODE_FRAME_BASED``
> > + - 1
> > + - Decoding is done at the frame granularity.
> > + v4l2_ctrl_h264_decode_params->num_slices should be set to the number of
> > + slices forming a frame.
>
> And start_byte_offset should be filled in accordingly for each slice.
>
OK.
Thanks,
Ezequiel
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