Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/csky/kernel/head.S b/arch/csky/kernel/head.S
new file mode 100644
index 0000000..61989f9
--- /dev/null
+++ b/arch/csky/kernel/head.S
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <linux/linkage.h>
+#include <linux/init.h>
+#include <asm/page.h>
+#include <abi/entry.h>
+
+__HEAD
+ENTRY(_start)
+	SETUP_MMU
+
+	/* set stack point */
+	lrw     r6, init_thread_union + THREAD_SIZE
+	mov	sp, r6
+
+	jmpi	csky_start
+END(_start)
+
+#ifdef CONFIG_SMP
+.align 10
+ENTRY(_start_smp_secondary)
+	SETUP_MMU
+
+	/* set stack point */
+	lrw     r6, secondary_stack
+	ld.w	r6, (r6, 0)
+	mov	sp, r6
+
+	jmpi	csky_start_secondary
+END(_start_smp_secondary)
+#endif