fastboot: add support for continue command

The fastboot continue command is defined to exit fastboot and continue
autoboot. This commit implements the continue command and the exiting of
fastboot only. Subsequent u-boot commands can be processed after exiting
fastboot. Autoboot should implement a boot script such as "fastboot; mmc
read <...>; bootm" to fully implement the fastboot continue function.

Signed-off-by: Rob Herring <robh@kernel.org>
Tested-by: Lukasz Majewski <l.majewski@samsung.com>
[TestHW: Exynos4412-Trats2]
diff --git a/drivers/usb/gadget/f_fastboot.c b/drivers/usb/gadget/f_fastboot.c
index 71b62e5..310175a 100644
--- a/drivers/usb/gadget/f_fastboot.c
+++ b/drivers/usb/gadget/f_fastboot.c
@@ -480,6 +480,17 @@
 	fastboot_tx_write_str("OKAY");
 }
 
+static void do_exit_on_complete(struct usb_ep *ep, struct usb_request *req)
+{
+	g_dnl_trigger_detach();
+}
+
+static void cb_continue(struct usb_ep *ep, struct usb_request *req)
+{
+	fastboot_func->in_req->complete = do_exit_on_complete;
+	fastboot_tx_write_str("OKAY");
+}
+
 #ifdef CONFIG_FASTBOOT_FLASH
 static void cb_flash(struct usb_ep *ep, struct usb_request *req)
 {
@@ -520,6 +531,9 @@
 	}, {
 		.cmd = "boot",
 		.cb = cb_boot,
+	}, {
+		.cmd = "continue",
+		.cb = cb_continue,
 	},
 #ifdef CONFIG_FASTBOOT_FLASH
 	{