cmd: add sdp command

Add a new command to start USB Serial Download Protocol (SDP)
state machine.

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
Reviewed-by: Łukasz Majewski <lukma@denx.de>
Reviewed-by: Stefano Babic <sbabic@denx.de>

cmd/usb_gadget_sdp.c

@@ -0,0 +1,50 @@
+/*
+ * cmd_sdp.c -- sdp command
+ *
+ * Copyright (C) 2016 Toradex
+ * Author: Stefan Agner <stefan.agner@toradex.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <g_dnl.h>
+#include <sdp.h>
+#include <usb.h>
+
+static int do_sdp(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
+{
+	int ret = CMD_RET_FAILURE;
+
+	if (argc < 2)
+		return CMD_RET_USAGE;
+
+	char *usb_controller = argv[1];
+	int controller_index = simple_strtoul(usb_controller, NULL, 0);
+	board_usb_init(controller_index, USB_INIT_DEVICE);
+
+	g_dnl_clear_detach();
+	g_dnl_register("usb_dnl_sdp");
+
+	ret = sdp_init(controller_index);
+	if (ret) {
+		error("SDP init failed: %d", ret);
+		goto exit;
+	}
+
+	/* This command typically does not return but jumps to an image */
+	sdp_handle(controller_index);
+	error("SDP ended");
+
+exit:
+	g_dnl_unregister();
+	board_usb_cleanup(controller_index, USB_INIT_DEVICE);
+
+	return ret;
+}
+
+U_BOOT_CMD(sdp, 2, 1, do_sdp,
+	"Serial Downloader Protocol",
+	"<USB_controller>\n"
+	"  - serial downloader protocol via <USB_controller>\n"
+);