[PATCH RFC 02/11] media: h264: Support picture order count type 2 in stateless encode

[Arun Iyengar via B4 Relay <devnull+aiyengar1990.gmail.com@kernel.org>]

From: Arun Iyengar <aiyengar1990@gmail.com>

Some encoders write the slice header in hardware and can't put a
pic_order_cnt_lsb in it: the Hantro H1 and Rockchip VEPU1/VEPU2 encoders
only produce slice headers for pic_order_cnt_type 2, where the picture
order count is derived from frame_num.

Accept pic_order_cnt_type 2, which drivers can then select in their
state_constrain operation, and compute the picture order count as
specified in ITU-T H.264 section 8.2.1.3. This needs the frame_num and
FrameNumOffset of the previous picture in decoding order, which are now
tracked for every picture, reference or not.

Type 2 implies that the output order is the decoding order, which is
always the case without B frames. Type 1 is still rejected.

Signed-off-by: Arun Iyengar <aiyengar1990@gmail.com>
---
 drivers/media/v4l2-core/v4l2-h264-enc-rbsp.c |  3 +-
 drivers/media/v4l2-core/v4l2-h264-enc.c      | 51 +++++++++++++++++++++++++---
 include/media/v4l2-h264-enc.h                |  3 ++
 3 files changed, 52 insertions(+), 5 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-h264-enc-rbsp.c b/drivers/media/v4l2-core/v4l2-h264-enc-rbsp.c
index a165f8114ce9..2d751855195b 100644
--- a/drivers/media/v4l2-core/v4l2-h264-enc-rbsp.c
+++ b/drivers/media/v4l2-core/v4l2-h264-enc-rbsp.c
@@ -758,7 +758,8 @@ int v4l2_h264_enc_rbsp_sps(struct v4l2_h264_enc_rbsp *rbsp,
 			if (ret)
 				return ret;
 		}
-	} else {
+	} else if (sps->pic_order_cnt_type != 2) {
+		/* Type 2 has no further syntax elements. */
 		return -EINVAL;
 	}
 
diff --git a/drivers/media/v4l2-core/v4l2-h264-enc.c b/drivers/media/v4l2-core/v4l2-h264-enc.c
index af925b6626cf..9745c0e85ee5 100644
--- a/drivers/media/v4l2-core/v4l2-h264-enc.c
+++ b/drivers/media/v4l2-core/v4l2-h264-enc.c
@@ -200,10 +200,11 @@ static int state_prepare_params(struct v4l2_h264_enc *enc)
 	sps->pic_height_in_map_units_minus1 = state->height_mbs - 1;
 
 	/*
-	 * Only pic_order_cnt_type = 0 is currently supported.
-	 * Error out since no pic_order_cnt_lsb was provided.
+	 * Only pic_order_cnt_type 0 and 2 are currently supported. Type 2
+	 * derives the picture order count from frame_num, for hardware that
+	 * can't write pic_order_cnt_lsb in the slice header.
 	 */
-	if (sps->pic_order_cnt_type)
+	if (sps->pic_order_cnt_type == 1)
 		return -EINVAL;
 
 	/* SPS Video */
@@ -933,6 +934,41 @@ static int ref_step_buffers(struct v4l2_h264_enc *enc)
 	return 0;
 }
 
+/* Picture order count type 2, see ITU-T H.264 section 8.2.1.3. */
+static int ref_step_poc_type2(struct v4l2_h264_enc *enc)
+{
+	struct v4l2_h264_enc_state *state = &enc->state_active;
+	struct v4l2_ctrl_h264_sps *sps = &state->sps;
+	struct v4l2_ctrl_h264_encode_params *encode = &state->encode;
+	struct v4l2_h264_enc_ref *ref = &enc->ref;
+	unsigned int max_frame_num = BIT(sps->log2_max_frame_num_minus4 + 4);
+	unsigned int frame_num_offset;
+	unsigned int pic_order_cnt;
+
+	if (encode->flags & V4L2_H264_ENCODE_FLAG_IDR_PIC)
+		frame_num_offset = 0;
+	else if (ref->prev_frame_num > encode->frame_num)
+		frame_num_offset = ref->prev_frame_num_offset + max_frame_num;
+	else
+		frame_num_offset = ref->prev_frame_num_offset;
+
+	if (encode->flags & V4L2_H264_ENCODE_FLAG_IDR_PIC)
+		pic_order_cnt = 0;
+	else if (!encode->nal_ref_idc)
+		pic_order_cnt = 2 * (frame_num_offset + encode->frame_num) - 1;
+	else
+		pic_order_cnt = 2 * (frame_num_offset + encode->frame_num);
+
+	ref->frame_num_offset = frame_num_offset;
+	ref->pic_order_cnt_msb = 0;
+	ref->pic_order_cnt_lsb = 0;
+	ref->top_field_order_cnt = pic_order_cnt;
+	ref->bottom_field_order_cnt = pic_order_cnt;
+	ref->pic_order_cnt = pic_order_cnt;
+
+	return 0;
+}
+
 static int ref_step_poc(struct v4l2_h264_enc *enc)
 {
 	struct v4l2_h264_enc_state *state = &enc->state_active;
@@ -949,7 +985,10 @@ static int ref_step_poc(struct v4l2_h264_enc *enc)
 	unsigned int top_field_order_cnt;
 	unsigned int bottom_field_order_cnt;
 
-	/* Only pic_order_cnt_type = 0 is currently supported. */
+	if (sps->pic_order_cnt_type == 2)
+		return ref_step_poc_type2(enc);
+
+	/* Only pic_order_cnt_type 0 and 2 are currently supported. */
 	if (sps->pic_order_cnt_type)
 		return -EINVAL;
 
@@ -1174,6 +1213,10 @@ static int ref_complete(struct v4l2_h264_enc *enc,
 	unsigned int index;
 	int ret;
 
+	/* Keep the frame number of the previous picture for POC type 2. */
+	ref->prev_frame_num = encode->frame_num;
+	ref->prev_frame_num_offset = ref->frame_num_offset;
+
 	if (!encode->nal_ref_idc)
 		return 0;
 
diff --git a/include/media/v4l2-h264-enc.h b/include/media/v4l2-h264-enc.h
index 6debdc95232c..ff7166109551 100644
--- a/include/media/v4l2-h264-enc.h
+++ b/include/media/v4l2-h264-enc.h
@@ -54,6 +54,9 @@ struct v4l2_h264_enc_ref {
 
 	struct v4l2_h264_reflist_builder builder;
 
+	unsigned int prev_frame_num;
+	unsigned int prev_frame_num_offset;
+	unsigned int frame_num_offset;
 	unsigned int prev_pic_order_cnt_msb;
 	unsigned int prev_pic_order_cnt_lsb;
 	unsigned int pic_order_cnt_msb;

-- 
2.55.0