[PATCH 05/10] staging: media: cedrus: mpeg2: derive the field order of field pictures

[Jernej Skrabec <jernej.skrabec@gmail.com>]

The hardware uses the top field first bit of the picture header to tell
the first field of a frame from the second one. However,
top_field_first is always 0 in field pictures, so userspace passes
V4L2_MPEG2_PIC_FLAG_TOP_FIELD_FIRST cleared, and the second field of
every top field first pair is predicted from the wrong reference.

Detect the second field in the driver instead: it has the opposite
parity of the previous field and is decoded into the same capture
buffer. This works with unmodified userspace.

Fixes: 50e761516f2b ("media: platform: Add Cedrus VPU decoder driver")
Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
---
 drivers/staging/media/sunxi/cedrus/cedrus.h   |  5 +++
 .../staging/media/sunxi/cedrus/cedrus_mpeg2.c | 32 +++++++++++++++++--
 2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/media/sunxi/cedrus/cedrus.h b/drivers/staging/media/sunxi/cedrus/cedrus.h
index 54f867949fba..a523b56a9b8c 100644
--- a/drivers/staging/media/sunxi/cedrus/cedrus.h
+++ b/drivers/staging/media/sunxi/cedrus/cedrus.h
@@ -144,6 +144,11 @@ struct cedrus_ctx {
 			void		*entry_points_buf;
 			dma_addr_t	entry_points_buf_addr;
 		} h265;
+		struct {
+			bool		pair_pending;
+			unsigned int	pair_dst;
+			u8		pair_structure;
+		} mpeg2;
 		struct {
 			unsigned int	last_frame_p_type;
 			unsigned int	last_filter_type;
diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_mpeg2.c b/drivers/staging/media/sunxi/cedrus/cedrus_mpeg2.c
index ca66a3c6b830..4c8accee5389 100644
--- a/drivers/staging/media/sunxi/cedrus/cedrus_mpeg2.c
+++ b/drivers/staging/media/sunxi/cedrus/cedrus_mpeg2.c
@@ -58,7 +58,7 @@ static int cedrus_mpeg2_setup(struct cedrus_ctx *ctx, struct cedrus_run *run)
 	struct vb2_queue *vq;
 	const u8 *matrix;
 	unsigned int i;
-	bool field;
+	bool field, tff;
 	u32 reg;
 
 	seq = run->mpeg2.sequence;
@@ -87,6 +87,26 @@ static int cedrus_mpeg2_setup(struct cedrus_ctx *ctx, struct cedrus_run *run)
 		cedrus_write(dev, VE_DEC_MPEG_IQMINPUT, reg);
 	}
 
+	/*
+	 * top_field_first is always 0 in field pictures, but the hardware
+	 * uses this bit to tell the first field of a frame from the second.
+	 * A field is the second one when it has the opposite parity of the
+	 * previous field and is decoded into the same capture buffer.
+	 */
+	if (pic->picture_structure == V4L2_MPEG2_PIC_FRAME) {
+		tff = !!(pic->flags & V4L2_MPEG2_PIC_FLAG_TOP_FIELD_FIRST);
+		ctx->codec.mpeg2.pair_pending = false;
+	} else {
+		bool second = ctx->codec.mpeg2.pair_pending &&
+			      ctx->codec.mpeg2.pair_structure != pic->picture_structure &&
+			      ctx->codec.mpeg2.pair_dst == run->dst->vb2_buf.index;
+
+		tff = (pic->picture_structure == V4L2_MPEG2_PIC_TOP_FIELD) != second;
+		ctx->codec.mpeg2.pair_pending = !second;
+		ctx->codec.mpeg2.pair_structure = pic->picture_structure;
+		ctx->codec.mpeg2.pair_dst = run->dst->vb2_buf.index;
+	}
+
 	/* Set MPEG picture header. */
 
 	reg = VE_DEC_MPEG_MP12HDR_SLICE_TYPE(pic->picture_coding_type);
@@ -96,7 +116,7 @@ static int cedrus_mpeg2_setup(struct cedrus_ctx *ctx, struct cedrus_run *run)
 	reg |= VE_DEC_MPEG_MP12HDR_F_CODE(1, 1, pic->f_code[1][1]);
 	reg |= VE_DEC_MPEG_MP12HDR_INTRA_DC_PRECISION(pic->intra_dc_precision);
 	reg |= VE_DEC_MPEG_MP12HDR_INTRA_PICTURE_STRUCTURE(pic->picture_structure);
-	reg |= VE_DEC_MPEG_MP12HDR_TOP_FIELD_FIRST(pic->flags & V4L2_MPEG2_PIC_FLAG_TOP_FIELD_FIRST);
+	reg |= VE_DEC_MPEG_MP12HDR_TOP_FIELD_FIRST(tff);
 	reg |= VE_DEC_MPEG_MP12HDR_FRAME_PRED_FRAME_DCT(pic->flags & V4L2_MPEG2_PIC_FLAG_FRAME_PRED_DCT);
 	reg |= VE_DEC_MPEG_MP12HDR_CONCEALMENT_MOTION_VECTORS(pic->flags & V4L2_MPEG2_PIC_FLAG_CONCEALMENT_MV);
 	reg |= VE_DEC_MPEG_MP12HDR_Q_SCALE_TYPE(pic->flags & V4L2_MPEG2_PIC_FLAG_Q_SCALE_TYPE);
@@ -186,6 +206,13 @@ static int cedrus_mpeg2_setup(struct cedrus_ctx *ctx, struct cedrus_run *run)
 	return 0;
 }
 
+static int cedrus_mpeg2_start(struct cedrus_ctx *ctx)
+{
+	memset(&ctx->codec.mpeg2, 0, sizeof(ctx->codec.mpeg2));
+
+	return 0;
+}
+
 static void cedrus_mpeg2_trigger(struct cedrus_ctx *ctx)
 {
 	struct cedrus_dev *dev = ctx->dev;
@@ -203,5 +230,6 @@ struct cedrus_dec_ops cedrus_dec_ops_mpeg2 = {
 	.irq_disable	= cedrus_mpeg2_irq_disable,
 	.irq_status	= cedrus_mpeg2_irq_status,
 	.setup		= cedrus_mpeg2_setup,
+	.start		= cedrus_mpeg2_start,
 	.trigger	= cedrus_mpeg2_trigger,
 };
-- 
2.43.0