media: uapi: h264: Rename and clarify PPS_FLAG_SCALING_MATRIX_PRESENT

Applications are expected to fill V4L2_CID_MPEG_VIDEO_H264_SCALING_MATRIX
if a non-flat scaling matrix applies to the picture. This is the case if
SPS scaling_matrix_present_flag or PPS pic_scaling_matrix_present_flag
are set, and should be handled by applications.

On one hand, the PPS bitstream syntax element signals the presence of a
Picture scaling matrix modifying the Sequence (SPS) scaling matrix.
On the other hand, our flag should indicate if the scaling matrix
V4L2 control is applicable to this request.

Rename the flag from PPS_FLAG_PIC_SCALING_MATRIX_PRESENT to
PPS_FLAG_SCALING_MATRIX_PRESENT, to avoid mixing this flag with
bitstream syntax element pic_scaling_matrix_present_flag,
and clarify the meaning of our flag.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Tested-by: Jonas Karlman <jonas@kwiboo.se>
Signed-off-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

@@ -1695,9 +1695,10 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
     * - ``V4L2_H264_PPS_FLAG_TRANSFORM_8X8_MODE``
       - 0x00000040
       -
-    * - ``V4L2_H264_PPS_FLAG_PIC_SCALING_MATRIX_PRESENT``
+    * - ``V4L2_H264_PPS_FLAG_SCALING_MATRIX_PRESENT``
       - 0x00000080
-      -
+      - Indicates that ``V4L2_CID_MPEG_VIDEO_H264_SCALING_MATRIX``
+        must be used for this picture.
 
 ``V4L2_CID_MPEG_VIDEO_H264_SCALING_MATRIX (struct)``
     Specifies the scaling matrix (as extracted from the bitstream) for

include/media/h264-ctrls.h

@@ -99,7 +99,7 @@ struct v4l2_ctrl_h264_sps {
 #define V4L2_H264_PPS_FLAG_CONSTRAINED_INTRA_PRED			0x0010
 #define V4L2_H264_PPS_FLAG_REDUNDANT_PIC_CNT_PRESENT			0x0020
 #define V4L2_H264_PPS_FLAG_TRANSFORM_8X8_MODE				0x0040
-#define V4L2_H264_PPS_FLAG_PIC_SCALING_MATRIX_PRESENT			0x0080
+#define V4L2_H264_PPS_FLAG_SCALING_MATRIX_PRESENT			0x0080
 
 struct v4l2_ctrl_h264_pps {
 	__u8 pic_parameter_set_id;