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

@@ -1142,6 +1142,11 @@ if BLK_DEV_INITRD
 
 source "usr/Kconfig"
 
+config INITRD_ASYNC
+	bool "Initrd async"
+	help
+	  Init ramdisk async, can reduce kernel init time.
+
 endif
 
 choice

init/initramfs.c

@@ -673,4 +673,23 @@ static int __init populate_rootfs(void)
 
 	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

@@ -1160,6 +1160,10 @@ static noinline void __init kernel_init_freeable(void)
 
 	do_basic_setup();
 
+#if IS_BUILTIN(CONFIG_INITRD_ASYNC)
+	async_synchronize_full();
+#endif
+
 	/* Open the /dev/console on the rootfs, this should never fail */
 	if (ksys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
 		pr_err("Warning: unable to open an initial console.\n");