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Date: Fri, 16 Aug 2019 16:43:19 +0200
From: Hans Verkuil <hverkuil@...all.nl>
To: Ezequiel Garcia <ezequiel@...labora.com>,
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 8/16/19 9:34 AM, 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.
>
> 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.
And for FRAME_BASED mode the offset for the first slice should also be 0.
This to avoid users from trying to abuse this to skip initial headers.
>
>> * - __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.
>
>> + 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.
With a note that the first slice should start at 0.
Regards,
Hans
>
> Regards,
>
> Hans
>
>> + The OUTPUT buffer must contain all slices needed to decode the
>> + frame. The OUTPUT buffer must also contain both fields.
>> +
>> .. _v4l2-mpeg-mpeg2:
>>
>> ``V4L2_CID_MPEG_VIDEO_MPEG2_SLICE_PARAMS (struct)``
>> diff --git a/Documentation/media/uapi/v4l/pixfmt-compressed.rst b/Documentation/media/uapi/v4l/pixfmt-compressed.rst
>> index 9b65473a2288..d666eb51741a 100644
>> --- a/Documentation/media/uapi/v4l/pixfmt-compressed.rst
>> +++ b/Documentation/media/uapi/v4l/pixfmt-compressed.rst
>> @@ -60,8 +60,10 @@ Compressed Formats
>> extracted from the H264 bitstream. This format is adapted for
>> stateless video decoders that implement an H264 pipeline
>> (using the :ref:`mem2mem` and :ref:`media-request-api`).
>> - Metadata associated with the frame to decode are required to
>> - be passed through the ``V4L2_CID_MPEG_VIDEO_H264_SPS``,
>> + This pixelformat has a modifier that must be set at least once
>> + through the ``V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE`` control.
>> + In addition, metadata associated with the frame to decode are
>> + required to be passed through the ``V4L2_CID_MPEG_VIDEO_H264_SPS``,
>> ``V4L2_CID_MPEG_VIDEO_H264_PPS``,
>> ``V4L2_CID_MPEG_VIDEO_H264_SCALING_MATRIX``,
>> ``V4L2_CID_MPEG_VIDEO_H264_SLICE_PARAMS`` and
>> diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
>> index cd1ae016706f..2c67f9fc4d5b 100644
>> --- a/drivers/media/v4l2-core/v4l2-ctrls.c
>> +++ b/drivers/media/v4l2-core/v4l2-ctrls.c
>> @@ -402,6 +402,11 @@ const char * const *v4l2_ctrl_get_menu(u32 id)
>> "Explicit",
>> NULL,
>> };
>> + static const char * const h264_decode_mode[] = {
>> + "Slice-Based",
>> + "Frame-Based",
>> + NULL,
>> + };
>> static const char * const mpeg_mpeg2_level[] = {
>> "Low",
>> "Main",
>> @@ -633,6 +638,8 @@ const char * const *v4l2_ctrl_get_menu(u32 id)
>> return h264_fp_arrangement_type;
>> case V4L2_CID_MPEG_VIDEO_H264_FMO_MAP_TYPE:
>> return h264_fmo_map_type;
>> + case V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE:
>> + return h264_decode_mode;
>> case V4L2_CID_MPEG_VIDEO_MPEG2_LEVEL:
>> return mpeg_mpeg2_level;
>> case V4L2_CID_MPEG_VIDEO_MPEG2_PROFILE:
>> @@ -852,6 +859,7 @@ const char *v4l2_ctrl_get_name(u32 id)
>> case V4L2_CID_MPEG_VIDEO_H264_SCALING_MATRIX: return "H264 Scaling Matrix";
>> case V4L2_CID_MPEG_VIDEO_H264_SLICE_PARAMS: return "H264 Slice Parameters";
>> case V4L2_CID_MPEG_VIDEO_H264_DECODE_PARAMS: return "H264 Decode Parameters";
>> + case V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE: return "H264 Decode Mode";
>> case V4L2_CID_MPEG_VIDEO_MPEG2_LEVEL: return "MPEG2 Level";
>> case V4L2_CID_MPEG_VIDEO_MPEG2_PROFILE: return "MPEG2 Profile";
>> case V4L2_CID_MPEG_VIDEO_MPEG4_I_FRAME_QP: return "MPEG4 I-Frame QP Value";
>> @@ -1220,6 +1228,7 @@ void v4l2_ctrl_fill(u32 id, const char **name, enum v4l2_ctrl_type *type,
>> case V4L2_CID_MPEG_VIDEO_H264_VUI_SAR_IDC:
>> case V4L2_CID_MPEG_VIDEO_H264_SEI_FP_ARRANGEMENT_TYPE:
>> case V4L2_CID_MPEG_VIDEO_H264_FMO_MAP_TYPE:
>> + case V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE:
>> case V4L2_CID_MPEG_VIDEO_MPEG2_LEVEL:
>> case V4L2_CID_MPEG_VIDEO_MPEG2_PROFILE:
>> case V4L2_CID_MPEG_VIDEO_MPEG4_LEVEL:
>> diff --git a/include/media/h264-ctrls.h b/include/media/h264-ctrls.h
>> index 6160a69c0143..928c48c57282 100644
>> --- a/include/media/h264-ctrls.h
>> +++ b/include/media/h264-ctrls.h
>> @@ -26,6 +26,7 @@
>> #define V4L2_CID_MPEG_VIDEO_H264_SCALING_MATRIX (V4L2_CID_MPEG_BASE+1002)
>> #define V4L2_CID_MPEG_VIDEO_H264_SLICE_PARAMS (V4L2_CID_MPEG_BASE+1003)
>> #define V4L2_CID_MPEG_VIDEO_H264_DECODE_PARAMS (V4L2_CID_MPEG_BASE+1004)
>> +#define V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE (V4L2_CID_MPEG_BASE+1005)
>>
>> /* enum v4l2_ctrl_type type values */
>> #define V4L2_CTRL_TYPE_H264_SPS 0x0110
>> @@ -34,6 +35,11 @@
>> #define V4L2_CTRL_TYPE_H264_SLICE_PARAMS 0x0113
>> #define V4L2_CTRL_TYPE_H264_DECODE_PARAMS 0x0114
>>
>> +enum v4l2_mpeg_video_h264_decode_mode {
>> + V4L2_MPEG_VIDEO_H264_DECODE_MODE_SLICE_BASED,
>> + V4L2_MPEG_VIDEO_H264_DECODE_MODE_FRAME_BASED,
>> +};
>> +
>> #define V4L2_H264_SPS_CONSTRAINT_SET0_FLAG 0x01
>> #define V4L2_H264_SPS_CONSTRAINT_SET1_FLAG 0x02
>> #define V4L2_H264_SPS_CONSTRAINT_SET2_FLAG 0x04
>> @@ -125,6 +131,10 @@ struct v4l2_h264_pred_weight_table {
>> struct v4l2_ctrl_h264_slice_params {
>> /* Size in bytes, including header */
>> __u32 size;
>> +
>> + /* Offset in bytes to the start of slice in the OUTPUT buffer. */
>> + __u32 start_byte_offset;
>> +
>> /* Offset in bits to slice_data() from the beginning of this slice. */
>> __u32 header_bit_size;
>>
>>
>
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