[PATCH] media: mediatek: vcodec: fix h264 cavlc bitstream fail

[Yunfei Dong <yunfei.dong@mediatek.com>]

Some cavlc bistream will decode fail when the frame size is small than
20 bytes. Need to add pending data at the end of the bitstream.

For the size of mapped memory is at least one page, adding four bytes data
won't lead to access unknown virtual memory.

Fixes: 59fba9eed5a7 ("media: mediatek: vcodec: support stateless H.264 decoding for mt8192")
Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
---
 .../vcodec/vdec/vdec_h264_req_multi_if.c      | 27 ++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/drivers/media/platform/mediatek/vcodec/vdec/vdec_h264_req_multi_if.c b/drivers/media/platform/mediatek/vcodec/vdec/vdec_h264_req_multi_if.c
index 4cc92700692b..c1583dddcb04 100644
--- a/drivers/media/platform/mediatek/vcodec/vdec/vdec_h264_req_multi_if.c
+++ b/drivers/media/platform/mediatek/vcodec/vdec/vdec_h264_req_multi_if.c
@@ -539,6 +539,24 @@ static int vdec_h264_slice_core_decode(struct vdec_lat_buf *lat_buf)
 	return 0;
 }
 
+static void vdec_h264_insert_startcode(struct mtk_vcodec_dev *vcodec_dev, unsigned char *buf,
+				       size_t *bs_size, struct mtk_h264_pps_param *pps)
+{
+	struct device *dev = &vcodec_dev->plat_dev->dev;
+
+	/* cavlc bitstream when entropy_coding_mode_flag is false. */
+	if (pps->entropy_coding_mode_flag || *bs_size > 20 ||
+	    !(of_device_is_compatible(dev->of_node, "mediatek,mt8192-vcodec-dec") ||
+	    of_device_is_compatible(dev->of_node, "mediatek,mt8195-vcodec-dec")))
+		return;
+
+	buf[*bs_size] = 0;
+	buf[*bs_size + 1] = 0;
+	buf[*bs_size + 2] = 1;
+	buf[*bs_size + 3] = 0xff;
+	(*bs_size) += 4;
+}
+
 static int vdec_h264_slice_lat_decode(void *h_vdec, struct mtk_vcodec_mem *bs,
 				      struct vdec_fb *fb, bool *res_chg)
 {
@@ -582,9 +600,6 @@ static int vdec_h264_slice_lat_decode(void *h_vdec, struct mtk_vcodec_mem *bs,
 	}
 
 	inst->vsi->dec.nal_info = buf[nal_start_idx];
-	inst->vsi->dec.bs_buf_addr = (u64)bs->dma_addr;
-	inst->vsi->dec.bs_buf_size = bs->size;
-
 	lat_buf->src_buf_req = src_buf_info->m2m_buf.vb.vb2_buf.req_obj.req;
 	v4l2_m2m_buf_copy_metadata(&src_buf_info->m2m_buf.vb, &lat_buf->ts_info, true);
 
@@ -592,6 +607,12 @@ static int vdec_h264_slice_lat_decode(void *h_vdec, struct mtk_vcodec_mem *bs,
 	if (err)
 		goto err_free_fb_out;
 
+	vdec_h264_insert_startcode(inst->ctx->dev, buf, &bs->size,
+				   &share_info->h264_slice_params.pps);
+
+	inst->vsi->dec.bs_buf_addr = (uint64_t)bs->dma_addr;
+	inst->vsi->dec.bs_buf_size = bs->size;
+
 	*res_chg = inst->resolution_changed;
 	if (inst->resolution_changed) {
 		mtk_vcodec_debug(inst, "- resolution changed -");
-- 
2.25.1