media: v4l: ctrls: Add a control for HDR mode

Add V4L2_CID_HDR_MODE as a menu item control to set the HDR mode of the
sensor, and its documentation.
Menu items are not standardized as they differ for each sensors.
Signed-off-by: Benjamin Mugnier <benjamin.mugnier@foss.st.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>

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

@@ -661,3 +661,11 @@ enum v4l2_scene_mode -
 .. [#f1]
    This control may be changed to a menu control in the future, if more
    options are required.
+
+``V4L2_CID_HDR_SENSOR_MODE (menu)``
+    Change the sensor HDR mode. A HDR picture is obtained by merging two
+    captures of the same scene using two different exposure periods. HDR mode
+    describes the way these two captures are merged in the sensor.
+
+    As modes differ for each sensor, menu items are not standardized by this
+    control and are left to the programmer.

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

@@ -1043,6 +1043,7 @@ const char *v4l2_ctrl_get_name(u32 id)
 	case V4L2_CID_UNIT_CELL_SIZE:		return "Unit Cell Size";
 	case V4L2_CID_CAMERA_ORIENTATION:	return "Camera Orientation";
 	case V4L2_CID_CAMERA_SENSOR_ROTATION:	return "Camera Sensor Rotation";
+	case V4L2_CID_HDR_SENSOR_MODE:		return "HDR Sensor Mode";
 
 	/* FM Radio Modulator controls */
 	/* Keep the order of the 'case's the same as in v4l2-controls.h! */
@@ -1370,6 +1371,7 @@ void v4l2_ctrl_fill(u32 id, const char **name, enum v4l2_ctrl_type *type,
 	case V4L2_CID_STATELESS_H264_START_CODE:
 	case V4L2_CID_CAMERA_ORIENTATION:
 	case V4L2_CID_MPEG_VIDEO_INTRA_REFRESH_PERIOD_TYPE:
+	case V4L2_CID_HDR_SENSOR_MODE:
 		*type = V4L2_CTRL_TYPE_MENU;
 		break;
 	case V4L2_CID_LINK_FREQ:

include/uapi/linux/v4l2-controls.h

@@ -1019,6 +1019,8 @@ enum v4l2_auto_focus_range {
 
 #define V4L2_CID_CAMERA_SENSOR_ROTATION		(V4L2_CID_CAMERA_CLASS_BASE+35)
 
+#define V4L2_CID_HDR_SENSOR_MODE		(V4L2_CID_CAMERA_CLASS_BASE+36)
+
 /* FM Modulator class control IDs */
 
 #define V4L2_CID_FM_TX_CLASS_BASE		(V4L2_CTRL_CLASS_FM_TX | 0x900)