Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/nds32/math-emu/fsubs.c b/arch/nds32/math-emu/fsubs.c
new file mode 100644
index 0000000..61ddd97
--- /dev/null
+++ b/arch/nds32/math-emu/fsubs.c
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2005-2018 Andes Technology Corporation
+#include <linux/uaccess.h>
+
+#include <asm/sfp-machine.h>
+#include <math-emu/soft-fp.h>
+#include <math-emu/single.h>
+void fsubs(void *ft, void *fa, void *fb)
+{
+
+	FP_DECL_S(A);
+	FP_DECL_S(B);
+	FP_DECL_S(R);
+	FP_DECL_EX;
+
+	FP_UNPACK_SP(A, fa);
+	FP_UNPACK_SP(B, fb);
+
+	if (B_c != FP_CLS_NAN)
+		B_s ^= 1;
+
+	FP_ADD_S(R, A, B);
+
+	FP_PACK_SP(ft, R);
+
+	__FPU_FPCSR |= FP_CUR_EXCEPTIONS;
+}