init: support init ramfs async

If enable ramfs function, init ramfs async,
can reduce kernel init time.

Change-Id: I95d8ca6d8b9c4e9c738c635c5ee56391cbbe7c16
Signed-off-by: Liao Huaping <huaping.liao@rock-chips.com>
Signed-off-by: Tao Huang <huangtao@rock-chips.com>

init/Kconfig

@@ -1310,6 +1310,11 @@ if BLK_DEV_INITRD
 
 source "usr/Kconfig"
 
+config INITRD_ASYNC
+	bool "Initrd async"
+	help
+	  Init ramdisk async, can reduce kernel init time.
+
 endif
 
 config BOOT_CONFIG

init/initramfs.c

@@ -639,4 +639,23 @@ done:
 	flush_delayed_fput();
 	return 0;
 }
+
+#if IS_BUILTIN(CONFIG_INITRD_ASYNC)
+#include <linux/kthread.h>
+#include <linux/async.h>
+
+static void __init unpack_rootfs_async(void *unused, async_cookie_t cookie)
+{
+	populate_rootfs();
+}
+
+static int __init populate_rootfs_async(void)
+{
+	async_schedule(unpack_rootfs_async, NULL);
+	return 0;
+}
+
+pure_initcall(populate_rootfs_async);
+#else
 rootfs_initcall(populate_rootfs);
+#endif

init/main.c

@@ -1550,6 +1550,10 @@ static noinline void __init kernel_init_freeable(void)
 
 	kunit_run_all_tests();
 
+#if IS_BUILTIN(CONFIG_INITRD_ASYNC)
+	async_synchronize_full();
+#endif
+
 	console_on_rootfs();
 
 	/*