media: v4l2-ctrls: Add encoder constant quality control

When V4L2_CID_MPEG_VIDEO_BITRATE_MODE value is
V4L2_MPEG_VIDEO_BITRATE_MODE_CQ, encoder will produce
constant quality output indicated by
V4L2_CID_MPEG_VIDEO_CONSTANT_QUALITY control value.
Encoder will choose appropriate quantization parameter
and bitrate to produce requested frame quality level.
Signed-off-by: Maheshwar Ajja <majja@codeaurora.org>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

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

@@ -581,6 +581,8 @@ enum v4l2_mpeg_video_bitrate_mode -
       - Variable bitrate
     * - ``V4L2_MPEG_VIDEO_BITRATE_MODE_CBR``
       - Constant bitrate
+    * - ``V4L2_MPEG_VIDEO_BITRATE_MODE_CQ``
+      - Constant quality
 
 
 
@@ -592,6 +594,14 @@ enum v4l2_mpeg_video_bitrate_mode -
     the average video bitrate. It is ignored if the video bitrate mode
     is set to constant bitrate.
 
+``V4L2_CID_MPEG_VIDEO_CONSTANT_QUALITY (integer)``
+    Constant quality level control. This control is applicable when
+    ``V4L2_CID_MPEG_VIDEO_BITRATE_MODE`` value is
+    ``V4L2_MPEG_VIDEO_BITRATE_MODE_CQ``. Valid range is 1 to 100
+    where 1 indicates lowest quality and 100 indicates highest quality.
+    Encoder will decide the appropriate quantization parameter and
+    bitrate to produce requested frame quality.
+
 ``V4L2_CID_MPEG_VIDEO_TEMPORAL_DECIMATION (integer)``
     For every captured frame, skip this many subsequent frames (default
     0).

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

@@ -200,6 +200,7 @@ const char * const *v4l2_ctrl_get_menu(u32 id)
 	static const char * const mpeg_video_bitrate_mode[] = {
 		"Variable Bitrate",
 		"Constant Bitrate",
+		"Constant Quality",
 		NULL
 	};
 	static const char * const mpeg_stream_type[] = {
@@ -832,6 +833,7 @@ const char *v4l2_ctrl_get_name(u32 id)
 	case V4L2_CID_MPEG_VIDEO_GOP_CLOSURE:	return "Video GOP Closure";
 	case V4L2_CID_MPEG_VIDEO_PULLDOWN:	return "Video Pulldown";
 	case V4L2_CID_MPEG_VIDEO_BITRATE_MODE:	return "Video Bitrate Mode";
+	case V4L2_CID_MPEG_VIDEO_CONSTANT_QUALITY:	return "Constant Quality";
 	case V4L2_CID_MPEG_VIDEO_BITRATE:	return "Video Bitrate";
 	case V4L2_CID_MPEG_VIDEO_BITRATE_PEAK:	return "Video Peak Bitrate";
 	case V4L2_CID_MPEG_VIDEO_TEMPORAL_DECIMATION: return "Video Temporal Decimation";

include/uapi/linux/v4l2-controls.h

@@ -375,6 +375,7 @@ enum v4l2_mpeg_video_aspect {
 enum v4l2_mpeg_video_bitrate_mode {
 	V4L2_MPEG_VIDEO_BITRATE_MODE_VBR = 0,
 	V4L2_MPEG_VIDEO_BITRATE_MODE_CBR = 1,
+	V4L2_MPEG_VIDEO_BITRATE_MODE_CQ  = 2,
 };
 #define V4L2_CID_MPEG_VIDEO_BITRATE		(V4L2_CID_MPEG_BASE+207)
 #define V4L2_CID_MPEG_VIDEO_BITRATE_PEAK	(V4L2_CID_MPEG_BASE+208)
@@ -742,6 +743,7 @@ enum v4l2_cid_mpeg_video_hevc_size_of_length_field {
 #define V4L2_CID_MPEG_VIDEO_HEVC_HIER_CODING_L6_BR	(V4L2_CID_MPEG_BASE + 642)
 #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)
 
 /*  MPEG-class control IDs specific to the CX2341x driver as defined by V4L2 */
 #define V4L2_CID_MPEG_CX2341X_BASE				(V4L2_CTRL_CLASS_MPEG | 0x1000)