media: v4l2: Reorder field reflist

As per spec, the field reflist requires interleaving top and bottom
field in a specific way that does not fit inside the sort operation.
The process consist of alternating references parity, starting with
a reference of the same parity as the current picture. This
processs is done twice, once for short term references and a second
time for the long term references.

Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Reviewed-by: Sebastian Fricke <sebastian.fricke@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

Author: ndufresne

drivers/media/v4l2-core/v4l2-h264.c

@@ -250,6 +250,40 @@ static int v4l2_h264_b1_ref_list_cmp(const void *ptra, const void *ptrb,
 	return poca < pocb ? -1 : 1;
 }
 
+/*
+ * The references need to be reordered so that references are alternating
+ * between top and bottom field references starting with the current picture
+ * parity. This has to be done for short term and long term references
+ * separately.
+ */
+static void reorder_field_reflist(const struct v4l2_h264_reflist_builder *b,
+				  struct v4l2_h264_reference *reflist)
+{
+	struct v4l2_h264_reference tmplist[V4L2_H264_REF_LIST_LEN];
+	u8 lt, i = 0, j = 0, k = 0;
+
+	memcpy(tmplist, reflist, sizeof(tmplist[0]) * b->num_valid);
+
+	for (lt = 0; lt <= 1; lt++) {
+		do {
+			for (; i < b->num_valid && b->refs[tmplist[i].index].longterm == lt; i++) {
+				if (tmplist[i].fields == b->cur_pic_fields) {
+					reflist[k++] = tmplist[i++];
+					break;
+				}
+			}
+
+			for (; j < b->num_valid && b->refs[tmplist[j].index].longterm == lt; j++) {
+				if (tmplist[j].fields != b->cur_pic_fields) {
+					reflist[k++] = tmplist[j++];
+					break;
+				}
+			}
+		} while ((i < b->num_valid && b->refs[tmplist[i].index].longterm == lt) ||
+			 (j < b->num_valid && b->refs[tmplist[j].index].longterm == lt));
+	}
+}
+
 static char ref_type_to_char(u8 ref_type)
 {
 	switch (ref_type) {
@@ -360,6 +394,9 @@ v4l2_h264_build_p_ref_list(const struct v4l2_h264_reflist_builder *builder,
 	sort_r(reflist, builder->num_valid, sizeof(*reflist),
 	       v4l2_h264_p_ref_list_cmp, NULL, builder);
 
+	if (builder->cur_pic_fields != V4L2_H264_FRAME_REF)
+		reorder_field_reflist(builder, reflist);
+
 	print_ref_list_p(builder, reflist);
 }
 EXPORT_SYMBOL_GPL(v4l2_h264_build_p_ref_list);
@@ -393,6 +430,11 @@ v4l2_h264_build_b_ref_lists(const struct v4l2_h264_reflist_builder *builder,
 	sort_r(b1_reflist, builder->num_valid, sizeof(*b1_reflist),
 	       v4l2_h264_b1_ref_list_cmp, NULL, builder);
 
+	if (builder->cur_pic_fields != V4L2_H264_FRAME_REF) {
+		reorder_field_reflist(builder, b0_reflist);
+		reorder_field_reflist(builder, b1_reflist);
+	}
+
 	if (builder->num_valid > 1 &&
 	    !memcmp(b1_reflist, b0_reflist, builder->num_valid))
 		swap(b1_reflist[0], b1_reflist[1]);