media: v4l2-ctrl: Add frame-skip std encoder control

Adds encoders standard v4l2 control for frame-skip. The control
is a copy of a custom encoder control so that other v4l2 encoder
drivers can use it.

Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst

@@ -602,6 +602,40 @@ enum v4l2_mpeg_video_bitrate_mode -
     Encoder will decide the appropriate quantization parameter and
     bitrate to produce requested frame quality.
 
+
+``V4L2_CID_MPEG_VIDEO_FRAME_SKIP_MODE (enum)``
+
+enum v4l2_mpeg_video_frame_skip_mode -
+    Indicates in what conditions the encoder should skip frames. If
+    encoding a frame would cause the encoded stream to be larger then a
+    chosen data limit then the frame will be skipped. Possible values
+    are:
+
+
+.. tabularcolumns:: |p{9.2cm}|p{8.3cm}|
+
+.. raw:: latex
+
+    \small
+
+.. flat-table::
+    :header-rows:  0
+    :stub-columns: 0
+
+    * - ``V4L2_MPEG_FRAME_SKIP_MODE_DISABLED``
+      - Frame skip mode is disabled.
+    * - ``V4L2_MPEG_FRAME_SKIP_MODE_LEVEL_LIMIT``
+      - Frame skip mode enabled and buffer limit is set by the chosen
+        level and is defined by the standard.
+    * - ``V4L2_MPEG_FRAME_SKIP_MODE_BUF_LIMIT``
+      - Frame skip mode enabled and buffer limit is set by the
+        :ref:`VBV (MPEG1/2/4) <v4l2-mpeg-video-vbv-size>` or
+        :ref:`CPB (H264) buffer size <v4l2-mpeg-video-h264-cpb-size>` control.
+
+.. raw:: latex
+
+    \normalsize
+
 ``V4L2_CID_MPEG_VIDEO_TEMPORAL_DECIMATION (integer)``
     For every captured frame, skip this many subsequent frames (default
     0).
@@ -1173,6 +1207,8 @@ enum v4l2_mpeg_video_h264_entropy_mode -
     Quantization parameter for an B frame for MPEG4. Valid range: from 1
     to 31.
 
+.. _v4l2-mpeg-video-vbv-size:
+
 ``V4L2_CID_MPEG_VIDEO_VBV_SIZE (integer)``
     The Video Buffer Verifier size in kilobytes, it is used as a
     limitation of frame skip. The VBV is defined in the standard as a
@@ -1210,6 +1246,8 @@ enum v4l2_mpeg_video_h264_entropy_mode -
     Force a key frame for the next queued buffer. Applicable to
     encoders. This is a general, codec-agnostic keyframe control.
 
+.. _v4l2-mpeg-video-h264-cpb-size:
+
 ``V4L2_CID_MPEG_VIDEO_H264_CPB_SIZE (integer)``
     The Coded Picture Buffer size in kilobytes, it is used as a
     limitation of frame skip. The CPB is defined in the H264 standard as

drivers/media/v4l2-core/v4l2-ctrls.c

@@ -591,6 +591,12 @@ const char * const *v4l2_ctrl_get_menu(u32 id)
 		"External",
 		NULL,
 	};
+	static const char * const mpeg_video_frame_skip[] = {
+		"Disabled",
+		"Level Limit",
+		"VBV/CPB Limit",
+		NULL,
+	};
 
 	switch (id) {
 	case V4L2_CID_MPEG_AUDIO_SAMPLING_FREQ:
@@ -652,6 +658,8 @@ const char * const *v4l2_ctrl_get_menu(u32 id)
 		return flash_strobe_source;
 	case V4L2_CID_MPEG_VIDEO_HEADER_MODE:
 		return header_mode;
+	case V4L2_CID_MPEG_VIDEO_FRAME_SKIP_MODE:
+		return mpeg_video_frame_skip;
 	case V4L2_CID_MPEG_VIDEO_MULTI_SLICE_MODE:
 		return multi_slice;
 	case V4L2_CID_MPEG_VIDEO_H264_ENTROPY_MODE:
@@ -846,6 +854,7 @@ const char *v4l2_ctrl_get_name(u32 id)
 	case V4L2_CID_MPEG_VIDEO_MB_RC_ENABLE:			return "H264 MB Level Rate Control";
 	case V4L2_CID_MPEG_VIDEO_HEADER_MODE:			return "Sequence Header Mode";
 	case V4L2_CID_MPEG_VIDEO_MAX_REF_PIC:			return "Max Number of Reference Pics";
+	case V4L2_CID_MPEG_VIDEO_FRAME_SKIP_MODE:		return "Frame Skip Mode";
 	case V4L2_CID_MPEG_VIDEO_H263_I_FRAME_QP:		return "H263 I-Frame QP Value";
 	case V4L2_CID_MPEG_VIDEO_H263_P_FRAME_QP:		return "H263 P-Frame QP Value";
 	case V4L2_CID_MPEG_VIDEO_H263_B_FRAME_QP:		return "H263 B-Frame QP Value";
@@ -1268,6 +1277,7 @@ void v4l2_ctrl_fill(u32 id, const char **name, enum v4l2_ctrl_type *type,
 	case V4L2_CID_FLASH_LED_MODE:
 	case V4L2_CID_FLASH_STROBE_SOURCE:
 	case V4L2_CID_MPEG_VIDEO_HEADER_MODE:
+	case V4L2_CID_MPEG_VIDEO_FRAME_SKIP_MODE:
 	case V4L2_CID_MPEG_VIDEO_MULTI_SLICE_MODE:
 	case V4L2_CID_MPEG_VIDEO_H264_ENTROPY_MODE:
 	case V4L2_CID_MPEG_VIDEO_H264_LEVEL:

include/uapi/linux/v4l2-controls.h

@@ -744,6 +744,12 @@ enum v4l2_cid_mpeg_video_hevc_size_of_length_field {
 #define V4L2_CID_MPEG_VIDEO_REF_NUMBER_FOR_PFRAMES	(V4L2_CID_MPEG_BASE + 643)
 #define V4L2_CID_MPEG_VIDEO_PREPEND_SPSPPS_TO_IDR	(V4L2_CID_MPEG_BASE + 644)
 #define V4L2_CID_MPEG_VIDEO_CONSTANT_QUALITY		(V4L2_CID_MPEG_BASE + 645)
+#define V4L2_CID_MPEG_VIDEO_FRAME_SKIP_MODE		(V4L2_CID_MPEG_BASE + 646)
+enum v4l2_mpeg_video_frame_skip_mode {
+	V4L2_MPEG_VIDEO_FRAME_SKIP_MODE_DISABLED	= 0,
+	V4L2_MPEG_VIDEO_FRAME_SKIP_MODE_LEVEL_LIMIT	= 1,
+	V4L2_MPEG_VIDEO_FRAME_SKIP_MODE_BUF_LIMIT	= 2,
+};
 
 /*  MPEG-class control IDs specific to the CX2341x driver as defined by V4L2 */
 #define V4L2_CID_MPEG_CX2341X_BASE				(V4L2_CTRL_CLASS_MPEG | 0x1000)