media: v4l2-core: Add helpers to build the H264 P/B0/B1 reflists

Building those list is a standard procedure described in section
'8.2.4 Decoding process for reference picture lists construction' of
the H264 specification.

We already have 2 drivers needing the same logic (hantro and rkvdec) and
I suspect we will soon have more.

Let's provide generic helpers to create those lists.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

2 files changed, 92 insertions, 1 deletions

diff --git a/include/media/h264-ctrls.h b/include/media/h264-ctrls.h
index 1c6ff7d63bca..080fd1293c42 100644
--- a/include/media/h264-ctrls.h
+++ b/include/media/h264-ctrls.h
@@ -13,6 +13,12 @@
 
 #include <linux/videodev2.h>
 
+/*
+ * Maximum DPB size, as specified by section 'A.3.1 Level limits
+ * common to the Baseline, Main, and Extended profiles'.
+ */
+#define V4L2_H264_NUM_DPB_ENTRIES 16
+
 /* Our pixel format isn't stable at the moment */
 #define V4L2_PIX_FMT_H264_SLICE v4l2_fourcc('S', '2', '6', '4') /* H264 parsed slices */
 
@@ -201,7 +207,7 @@ struct v4l2_h264_dpb_entry {
 #define V4L2_H264_DECODE_PARAM_FLAG_IDR_PIC	0x01
 
 struct v4l2_ctrl_h264_decode_params {
-	struct v4l2_h264_dpb_entry dpb[16];
+	struct v4l2_h264_dpb_entry dpb[V4L2_H264_NUM_DPB_ENTRIES];
 	__u16 num_slices;
 	__u16 nal_ref_idc;
 	__s32 top_field_order_cnt;
diff --git a/include/media/v4l2-h264.h b/include/media/v4l2-h264.h
new file mode 100644
index 000000000000..bc9ebb560ccf
--- /dev/null
+++ b/include/media/v4l2-h264.h
@@ -0,0 +1,85 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Helper functions for H264 codecs.
+ *
+ * Copyright (c) 2019 Collabora, Ltd.
+ *
+ * Author: Boris Brezillon <boris.brezillon@collabora.com>
+ */
+
+#ifndef _MEDIA_V4L2_H264_H
+#define _MEDIA_V4L2_H264_H
+
+#include <media/h264-ctrls.h>
+
+/**
+ * struct v4l2_h264_reflist_builder - Reference list builder object
+ *
+ * @refs.pic_order_count: reference picture order count
+ * @refs.frame_num: reference frame number
+ * @refs.pic_num: reference picture number
+ * @refs.longterm: set to true for a long term reference
+ * @refs: array of references
+ * @cur_pic_order_count: picture order count of the frame being decoded
+ * @unordered_reflist: unordered list of references. Will be used to generate
+ *		       ordered P/B0/B1 lists
+ * @num_valid: number of valid references in the refs array
+ *
+ * This object stores the context of the P/B0/B1 reference list builder.
+ * This procedure is described in section '8.2.4 Decoding process for reference
+ * picture lists construction' of the H264 spec.
+ */
+struct v4l2_h264_reflist_builder {
+	struct {
+		s32 pic_order_count;
+		int frame_num;
+		u16 pic_num;
+		u16 longterm : 1;
+	} refs[V4L2_H264_NUM_DPB_ENTRIES];
+	s32 cur_pic_order_count;
+	u8 unordered_reflist[V4L2_H264_NUM_DPB_ENTRIES];
+	u8 num_valid;
+};
+
+void
+v4l2_h264_init_reflist_builder(struct v4l2_h264_reflist_builder *b,
+		const struct v4l2_ctrl_h264_decode_params *dec_params,
+		const struct v4l2_ctrl_h264_slice_params *slice_params,
+		const struct v4l2_ctrl_h264_sps *sps,
+		const struct v4l2_h264_dpb_entry dpb[V4L2_H264_NUM_DPB_ENTRIES]);
+
+/**
+ * v4l2_h264_build_b_ref_lists() - Build the B0/B1 reference lists
+ *
+ * @builder: reference list builder context
+ * @b0_reflist: 16-bytes array used to store the B0 reference list. Each entry
+ *		is an index in the DPB
+ * @b1_reflist: 16-bytes array used to store the B1 reference list. Each entry
+ *		is an index in the DPB
+ *
+ * This functions builds the B0/B1 reference lists. This procedure is described
+ * in section '8.2.4 Decoding process for reference picture lists construction'
+ * of the H264 spec. This function can be used by H264 decoder drivers that
+ * need to pass B0/B1 reference lists to the hardware.
+ */
+void
+v4l2_h264_build_b_ref_lists(const struct v4l2_h264_reflist_builder *builder,
+			    u8 *b0_reflist, u8 *b1_reflist);
+
+/**
+ * v4l2_h264_build_b_ref_lists() - Build the P reference list
+ *
+ * @builder: reference list builder context
+ * @p_reflist: 16-bytes array used to store the P reference list. Each entry
+ *	       is an index in the DPB
+ *
+ * This functions builds the P reference lists. This procedure is describe in
+ * section '8.2.4 Decoding process for reference picture lists construction'
+ * of the H264 spec. This function can be used by H264 decoder drivers that
+ * need to pass a P reference list to the hardware.
+ */
+void
+v4l2_h264_build_p_ref_list(const struct v4l2_h264_reflist_builder *builder,
+			   u8 *reflist);
+
+#endif /* _MEDIA_V4L2_H264_H */