[PATCH RFC 08/10] media: v4l2-hevc-enc: Add QP limits for the I pictures

[Arun Iyengar <aiyengar1990@gmail.com>]

The frame rate control of the core limits all pictures to the range of
V4L2_CID_MPEG_VIDEO_HEVC_MIN_QP and V4L2_CID_MPEG_VIDEO_HEVC_MAX_QP. The
I pictures, coded several QP steps below the P pictures, then reach very
low QP values at high bitrates, where they cost many bits for little
quality.

Take the limits of the I pictures from V4L2_CID_MPEG_VIDEO_HEVC_I_FRAME_MIN_QP
and V4L2_CID_MPEG_VIDEO_HEVC_I_FRAME_MAX_QP when the driver has them, with
a frame rate control. Without these controls, nothing changes.

Signed-off-by: Arun Iyengar <aiyengar1990@gmail.com>
---
 drivers/media/v4l2-core/v4l2-hevc-enc.c | 24 +++++++++++++++++++++---
 include/media/v4l2-hevc-enc.h           |  7 +++++++
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-hevc-enc.c b/drivers/media/v4l2-core/v4l2-hevc-enc.c
index a167c4af6288..2e0ba832b868 100644
--- a/drivers/media/v4l2-core/v4l2-hevc-enc.c
+++ b/drivers/media/v4l2-core/v4l2-hevc-enc.c
@@ -645,6 +645,12 @@ static void prepare_rc(struct v4l2_hevc_enc *enc,
 	state->qp_min = enc_ctrl_val(enc, V4L2_CID_MPEG_VIDEO_HEVC_MIN_QP,
 				     -qp_bd_offset);
 	state->qp_max = enc_ctrl_val(enc, V4L2_CID_MPEG_VIDEO_HEVC_MAX_QP, 51);
+	state->qp_min_i = enc_ctrl_val(enc,
+				       V4L2_CID_MPEG_VIDEO_HEVC_I_FRAME_MIN_QP,
+				       state->qp_min);
+	state->qp_max_i = enc_ctrl_val(enc,
+				       V4L2_CID_MPEG_VIDEO_HEVC_I_FRAME_MAX_QP,
+				       state->qp_max);
 	state->qp_i = enc_ctrl_val(enc, V4L2_CID_MPEG_VIDEO_HEVC_I_FRAME_QP, 30);
 	state->qp_p = enc_ctrl_val(enc, V4L2_CID_MPEG_VIDEO_HEVC_P_FRAME_QP,
 				   state->qp_i);
@@ -1072,10 +1078,23 @@ static bool rc_core_cbr(const struct v4l2_hevc_enc *enc,
 	       !(enc->rc_ops && enc->rc_ops->estimate);
 }
 
+/* QP limits of the picture: the I picture ones with a frame rate control */
+static int rc_clamp_qp(const struct v4l2_hevc_enc_state *state, int qp)
+{
+	int qp_bd_offset = 6 * state->sps.bit_depth_luma_minus8;
+
+	if (state->frame_rc_enable &&
+	    state->encode.slice_type == V4L2_HEVC_SLICE_TYPE_I)
+		qp = clamp(qp, state->qp_min_i, state->qp_max_i);
+	else
+		qp = clamp(qp, state->qp_min, state->qp_max);
+
+	return clamp(qp, -qp_bd_offset, 51);
+}
+
 static int rc_step(struct v4l2_hevc_enc *enc)
 {
 	struct v4l2_hevc_enc_state *state = &enc->state_active;
-	int qp_bd_offset = 6 * state->sps.bit_depth_luma_minus8;
 	u8 slice_type = state->encode.slice_type;
 	unsigned int range;
 	int qp, ret;
@@ -1114,8 +1133,7 @@ static int rc_step(struct v4l2_hevc_enc *enc)
 			return ret;
 	}
 
-	qp = clamp(qp, state->qp_min, state->qp_max);
-	enc->qp = clamp(qp, -qp_bd_offset, 51);
+	enc->qp = rc_clamp_qp(state, qp);
 
 	return 0;
 }
diff --git a/include/media/v4l2-hevc-enc.h b/include/media/v4l2-hevc-enc.h
index 3db131370c56..f1d3da3269f1 100644
--- a/include/media/v4l2-hevc-enc.h
+++ b/include/media/v4l2-hevc-enc.h
@@ -128,6 +128,11 @@ struct v4l2_hevc_enc_ref {
  * @frame_rc_enable: V4L2_CID_MPEG_VIDEO_FRAME_RC_ENABLE
  * @qp_min: V4L2_CID_MPEG_VIDEO_HEVC_MIN_QP
  * @qp_max: V4L2_CID_MPEG_VIDEO_HEVC_MAX_QP
+ * @qp_min_i: V4L2_CID_MPEG_VIDEO_HEVC_I_FRAME_MIN_QP, @qp_min if the driver
+ *	      has no such control. Limits the I pictures with a frame rate
+ *	      control instead of @qp_min.
+ * @qp_max_i: V4L2_CID_MPEG_VIDEO_HEVC_I_FRAME_MAX_QP, @qp_max if the driver
+ *	      has no such control
  * @qp_i: V4L2_CID_MPEG_VIDEO_HEVC_I_FRAME_QP
  * @qp_p: V4L2_CID_MPEG_VIDEO_HEVC_P_FRAME_QP
  * @qp_b: V4L2_CID_MPEG_VIDEO_HEVC_B_FRAME_QP
@@ -153,6 +158,8 @@ struct v4l2_hevc_enc_state {
 	bool frame_rc_enable;
 	int qp_min;
 	int qp_max;
+	int qp_min_i;
+	int qp_max_i;
 	int qp_i;
 	int qp_p;
 	int qp_b;

-- 
2.55.0