diff --git a/drivers/infiniband/hw/mlx5/wr.c b/drivers/infiniband/hw/mlx5/wr.c
index d6038fb6c50c655aa3048479ef6ad6d343113397..19fd440a6ce38bf8ba9ba431089c7eeeaa5e2a7f 100644
--- a/drivers/infiniband/hw/mlx5/wr.c
+++ b/drivers/infiniband/hw/mlx5/wr.c
@@ -128,7 +128,7 @@ static void set_eth_seg(const struct ib_send_wr *wr, struct mlx5_ib_qp *qp,
 		 */
 		copysz = min_t(u64, *cur_edge - (void *)eseg->inline_hdr.start,
 			       left);
-		memcpy(eseg->inline_hdr.start, pdata, copysz);
+		memcpy(eseg->inline_hdr.data, pdata, copysz);
 		stride = ALIGN(sizeof(struct mlx5_wqe_eth_seg) -
 			       sizeof(eseg->inline_hdr.start) + copysz, 16);
 		*size += stride / 16;
diff --git a/include/linux/mlx5/qp.h b/include/linux/mlx5/qp.h
index d75ef8aa8fac02840e917fd3057eb568704cba3d..28d44061d670041866181013bc609a411d4305f2 100644
--- a/include/linux/mlx5/qp.h
+++ b/include/linux/mlx5/qp.h
@@ -261,7 +261,10 @@ struct mlx5_wqe_eth_seg {
 	union {
 		struct {
 			__be16 sz;
-			u8     start[2];
+			union {
+				u8     start[2];
+				DECLARE_FLEX_ARRAY(u8, data);
+			};
 		} inline_hdr;
 		struct {
 			__be16 type;
diff --git a/include/linux/stddef.h b/include/linux/stddef.h
index 938216f8ab7e7c85d6d54f595a70023cead69b23..31fdbb784c24e211de7949cd1e4de7b7ff13a9d6 100644
--- a/include/linux/stddef.h
+++ b/include/linux/stddef.h
@@ -84,4 +84,17 @@ enum {
 #define struct_group_tagged(TAG, NAME, MEMBERS...) \
 	__struct_group(TAG, NAME, /* no attrs */, MEMBERS)
 
+/**
+ * DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
+ *
+ * @TYPE: The type of each flexible array element
+ * @NAME: The name of the flexible array member
+ *
+ * In order to have a flexible array member in a union or alone in a
+ * struct, it needs to be wrapped in an anonymous struct with at least 1
+ * named member, but that member can be empty.
+ */
+#define DECLARE_FLEX_ARRAY(TYPE, NAME) \
+	__DECLARE_FLEX_ARRAY(TYPE, NAME)
+
 #endif
diff --git a/include/uapi/linux/stddef.h b/include/uapi/linux/stddef.h
index c3725b4922632346ee99666d5f280fe4a85b7c61..7837ba4fe7289024c10942a7793411e0e3b27e7f 100644
--- a/include/uapi/linux/stddef.h
+++ b/include/uapi/linux/stddef.h
@@ -28,4 +28,20 @@
 		struct { MEMBERS } ATTRS; \
 		struct TAG { MEMBERS } ATTRS NAME; \
 	}
+
+/**
+ * __DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
+ *
+ * @TYPE: The type of each flexible array element
+ * @NAME: The name of the flexible array member
+ *
+ * In order to have a flexible array member in a union or alone in a
+ * struct, it needs to be wrapped in an anonymous struct with at least 1
+ * named member, but that member can be empty.
+ */
+#define __DECLARE_FLEX_ARRAY(TYPE, NAME)	\
+	struct { \
+		struct { } __empty_ ## NAME; \
+		TYPE NAME[]; \
+	}
 #endif
diff --git a/scripts/kernel-doc b/scripts/kernel-doc
index 19af6dd160e6b7e8ae2ad6c0bbe7360e8a558443..7a04d4c0532607880f1e38dc5b907d90d780c4d2 100755
--- a/scripts/kernel-doc
+++ b/scripts/kernel-doc
@@ -1232,7 +1232,8 @@ sub dump_struct($$) {
 	$members =~ s/DECLARE_KFIFO\s*\(([^,)]+),\s*([^,)]+),\s*([^,)]+)\)/$2 \*$1/gos;
 	# replace DECLARE_KFIFO_PTR
 	$members =~ s/DECLARE_KFIFO_PTR\s*\(([^,)]+),\s*([^,)]+)\)/$2 \*$1/gos;
-
+	# replace DECLARE_FLEX_ARRAY
+	$members =~ s/(?:__)?DECLARE_FLEX_ARRAY\s*\($args,\s*$args\)/$1 $2\[\]/gos;
 	my $declaration = $members;
 
 	# Split nested struct/union elements as newer ones