[PATCH v3 2/3] media: uapi: h264: Add the concept of decoding mode

Boris Brezillon
2019-07-03T12:28:57Z

Some stateless decoders don't support per-slice decoding (or at least
not in a way that would make them efficient or easy to use).
Let's expose a menu to control and expose the supported decoding modes.
Drivers are allowed to support only one decoding but they can support
both too.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
---
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 ++++++++++++++++++-
drivers/media/v4l2-core/v4l2-ctrls.c | 9 ++++
include/media/h264-ctrls.h | 13 +++++
3 files changed, 68 insertions(+), 1 deletion(-)

diff --git a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
index 3ae1367806cf..47ba2d057a92 100644
--- a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
+++ b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
@@ -1748,6 +1748,14 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
* - __u32
- ``size``
-
+ * - __u32
+ - ``start_byte_offset``
+ - Where the slice payload starts in the output buffer. Useful when
+ operating in frame-based decoding mode and decoding multi-slice
+ content. In this case, the output buffer will contain more than one
+ slice and some codecs need to know where each slice starts. Note that
+ this offsets points to the beginning of the slice which is supposed to
+ contain an ANNEX B start code
* - __u32
- ``header_bit_size``
-
@@ -1931,7 +1939,10 @@ 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_decoding_mode`), this field
+ should always be set to one
* - __u16
- ``nal_ref_idc``
- NAL reference ID value coming from the NAL Unit header
@@ -2022,6 +2033,40 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
- 0x00000004
- The DPB entry is a long term reference frame

+``V4L2_CID_MPEG_VIDEO_H264_DECODING_MODE (enum)``
+ Specifies the decoding mode to use. Currently exposes slice-based and
+ frame-based decoding but new modes might be added later on.
+
+ .. 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_decoding_mode
+
+.. cssclass:: longtable
+
+.. flat-table::
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 1 1 2
+
+ * - ``V4L2_MPEG_VIDEO_H264_SLICE_BASED_DECODING``
+ - 0
+ - The decoding is done at the slice granularity.
+ v4l2_ctrl_h264_decode_params->num_slices can be set to anything between
+ 1 and then number of slices that remain to fully decode the
+ frame/field.
+ The output buffer should contain
+ v4l2_ctrl_h264_decode_params->num_slices slices.
+ * - ``V4L2_MPEG_VIDEO_H264_FRAME_BASED_DECODING``
+ - 1
+ - The 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.
+ The output buffer should contain all slices needed to decode the
+ frame/field.
+
.. _v4l2-mpeg-mpeg2:

``V4L2_CID_MPEG_VIDEO_MPEG2_SLICE_PARAMS (struct)``
diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
index 471ff5c91f43..70d994be27e1 100644
--- a/drivers/media/v4l2-core/v4l2-ctrls.c
+++ b/drivers/media/v4l2-core/v4l2-ctrls.c
@@ -394,6 +394,11 @@ const char * const *v4l2_ctrl_get_menu(u32 id)
"Explicit",
NULL,
};
+ static const char * const h264_decoding_mode[] = {
+ "Slice-based",
+ "Frame-based",
+ NULL,
+ };
static const char * const mpeg_mpeg2_level[] = {
"Low",
"Main",
@@ -625,6 +630,8 @@ 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_DECODING_MODE:
+ return h264_decoding_mode;
case V4L2_CID_MPEG_VIDEO_MPEG2_LEVEL:
return mpeg_mpeg2_level;
case V4L2_CID_MPEG_VIDEO_MPEG2_PROFILE:
@@ -844,6 +851,7 @@ 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_DECODING_MODE: return "H264 Decoding 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";
@@ -1212,6 +1220,7 @@ 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_DECODING_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 e1404d78d6ff..206fd5ada620 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_DECODING_MODE (V4L2_CID_MPEG_BASE+1005)

/* enum v4l2_ctrl_type type values */
#define V4L2_CTRL_TYPE_H264_SPS 0x0110
@@ -33,6 +34,12 @@
#define V4L2_CTRL_TYPE_H264_SCALING_MATRIX 0x0112
#define V4L2_CTRL_TYPE_H264_SLICE_PARAMS 0x0113
#define V4L2_CTRL_TYPE_H264_DECODE_PARAMS 0x0114
+#define V4L2_CTRL_TYPE_H264_DECODING_MODE 0x0115
+
+enum v4l2_mpeg_video_h264_decoding_mode {
+ V4L2_MPEG_VIDEO_H264_SLICE_BASED_DECODING,
+ V4L2_MPEG_VIDEO_H264_FRAME_BASED_DECODING,
+};

#define V4L2_H264_SPS_CONSTRAINT_SET0_FLAG 0x01
#define V4L2_H264_SPS_CONSTRAINT_SET1_FLAG 0x02
@@ -111,6 +118,8 @@ struct v4l2_h264_pred_weight_table {
struct v4l2_h264_weight_factors weight_factors[2];
};

+#define V4L2_H264_MAX_SLICES_PER_FRAME 16
+
#define V4L2_H264_SLICE_TYPE_P 0
#define V4L2_H264_SLICE_TYPE_B 1
#define V4L2_H264_SLICE_TYPE_I 2
@@ -125,6 +134,10 @@ struct v4l2_h264_pred_weight_table {
struct v4l2_ctrl_h264_slice_params {
/* Size in bytes, including header */
__u32 size;
+
+ /* Where the slice starts in the output buffer (expressed in bytes). */
+ __u32 start_byte_offset;
+
/* Offset in bits to slice_data() from the beginning of this slice. */
__u32 header_bit_size;

--
2.21.0