media: uapi: h264: Add DPB entry field reference flags

Using the field information attached to v4l2 buffers is not enough to
determine the type of field referenced by a DPB entry: the decoded
frame might contain the full picture (both top and bottom fields)
but the reference only point to one of them.
Let's add new V4L2_H264_DPB_ENTRY_FLAG_ flags to express that.

[Keep only 2 flags and add some details about they mean]

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/media/uapi/v4l/ext-ctrls-codec.rst

@@ -2028,6 +2028,22 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
     * - ``V4L2_H264_DPB_ENTRY_FLAG_LONG_TERM``
       - 0x00000004
       - The DPB entry is a long term reference frame
+    * - ``V4L2_H264_DPB_ENTRY_FLAG_FIELD``
+      - 0x00000008
+      - The DPB entry is a field reference, which means only one of the field
+        will be used when decoding the new frame/field. When not set the DPB
+        entry is a frame reference (both fields will be used). Note that this
+        flag does not say anything about the number of fields contained in the
+        reference frame, it just describes the one used to decode the new
+        field/frame
+    * - ``V4L2_H264_DPB_ENTRY_FLAG_BOTTOM_FIELD``
+      - 0x00000010
+      - The DPB entry is a bottom field reference (only the bottom field of the
+        reference frame is needed to decode the new frame/field). Only valid if
+        V4L2_H264_DPB_ENTRY_FLAG_FIELD is set. When
+        V4L2_H264_DPB_ENTRY_FLAG_FIELD is set but
+        V4L2_H264_DPB_ENTRY_FLAG_BOTTOM_FIELD is not, that means the
+        DPB entry is a top field reference
 
 ``V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE (enum)``
     Specifies the decoding mode to use. Currently exposes slice-based and

include/media/h264-ctrls.h

@@ -185,6 +185,8 @@ struct v4l2_ctrl_h264_slice_params {
 #define V4L2_H264_DPB_ENTRY_FLAG_VALID		0x01
 #define V4L2_H264_DPB_ENTRY_FLAG_ACTIVE		0x02
 #define V4L2_H264_DPB_ENTRY_FLAG_LONG_TERM	0x04
+#define V4L2_H264_DPB_ENTRY_FLAG_FIELD		0x08
+#define V4L2_H264_DPB_ENTRY_FLAG_BOTTOM_FIELD	0x10
 
 struct v4l2_h264_dpb_entry {
 	__u64 reference_ts;