usb: gadget: add SDP driver

Add SDP (Serial Downloader Protocol) implementation for U-Boot. The
protocol is used in NXP SoC's boot ROM and allows to download program
images. Beside that, it can also be used to read/write registers and
download complete Device Configuration Data (DCD) sets. This basic
implementation supports downloading images with the imx header format
reading and writing registers.

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

4 files changed, 745 insertions, 0 deletions

diff --git a/drivers/usb/gadget/Kconfig b/drivers/usb/gadget/Kconfig
index 261ed128ac..225b66bc95 100644
--- a/drivers/usb/gadget/Kconfig
+++ b/drivers/usb/gadget/Kconfig
@@ -103,6 +103,13 @@ config USB_GADGET_DOWNLOAD
 
 if USB_GADGET_DOWNLOAD
 
+config USB_FUNCTION_SDP
+	bool "Enable USB SDP (Serial Download Protocol)"
+	help
+	  Enable Serial Download Protocol (SDP) device support in U-Boot. This
+	  allows to download images into memory and execute (jump to) them
+	  using the same protocol as implemented by the i.MX family's boot ROM.
+
 config G_DNL_MANUFACTURER
 	string "Vendor name of USB device"
 
diff --git a/drivers/usb/gadget/Makefile b/drivers/usb/gadget/Makefile
index 5e316a7cff..6a007d1bcb 100644
--- a/drivers/usb/gadget/Makefile
+++ b/drivers/usb/gadget/Makefile
@@ -28,6 +28,7 @@ obj-$(CONFIG_USB_FUNCTION_THOR) += f_thor.o
 obj-$(CONFIG_USB_FUNCTION_DFU) += f_dfu.o
 obj-$(CONFIG_USB_FUNCTION_MASS_STORAGE) += f_mass_storage.o
 obj-$(CONFIG_USB_FUNCTION_FASTBOOT) += f_fastboot.o
+obj-$(CONFIG_USB_FUNCTION_SDP) += f_sdp.o
 endif
 endif
 ifdef CONFIG_USB_ETHER
diff --git a/drivers/usb/gadget/f_sdp.c b/drivers/usb/gadget/f_sdp.c
new file mode 100644
index 0000000000..9d82abcd69
--- /dev/null
+++ b/drivers/usb/gadget/f_sdp.c
@@ -0,0 +1,721 @@
+/*
+ * f_sdp.c -- USB HID Serial Download Protocol
+ *
+ * Copyright (C) 2017 Toradex
+ * Author: Stefan Agner <stefan.agner@toradex.com>
+ *
+ * This file implements the Serial Download Protocol (SDP) as specified in
+ * the i.MX 6 Reference Manual. The SDP is a USB HID based protocol and
+ * allows to download images directly to memory. The implementation
+ * works with the imx_loader (imx_usb) USB client software on host side.
+ *
+ * Not all commands are implemented, e.g. WRITE_REGISTER, DCD_WRITE and
+ * SKIP_DCD_HEADER are only stubs.
+ *
+ * Parts of the implementation are based on f_dfu and f_thor.
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <errno.h>
+#include <common.h>
+#include <console.h>
+#include <malloc.h>
+
+#include <linux/usb/ch9.h>
+#include <linux/usb/gadget.h>
+#include <linux/usb/composite.h>
+
+#include <asm/io.h>
+#include <g_dnl.h>
+#include <sdp.h>
+#include <imximage.h>
+
+#define HID_REPORT_ID_MASK	0x000000ff
+
+/*
+ * HID class requests
+ */
+#define HID_REQ_GET_REPORT		0x01
+#define HID_REQ_GET_IDLE		0x02
+#define HID_REQ_GET_PROTOCOL		0x03
+#define HID_REQ_SET_REPORT		0x09
+#define HID_REQ_SET_IDLE		0x0A
+#define HID_REQ_SET_PROTOCOL		0x0B
+
+#define HID_USAGE_PAGE_LEN		76
+
+struct hid_report {
+	u8 usage_page[HID_USAGE_PAGE_LEN];
+} __packed;
+
+#define SDP_READ_REGISTER	0x0101
+#define SDP_WRITE_REGISTER	0x0202
+#define SDP_WRITE_FILE		0x0404
+#define SDP_ERROR_STATUS	0x0505
+#define SDP_DCD_WRITE		0x0a0a
+#define SDP_JUMP_ADDRESS	0x0b0b
+#define SDP_SKIP_DCD_HEADER	0x0c0c
+
+#define SDP_SECURITY_CLOSED		0x12343412
+#define SDP_SECURITY_OPEN		0x56787856
+
+#define SDP_WRITE_FILE_COMPLETE		0x88888888
+#define SDP_WRITE_REGISTER_COMPLETE	0x128A8A12
+#define SDP_SKIP_DCD_HEADER_COMPLETE	0x900DD009
+#define SDP_ERROR_IMXHEADER		0x000a0533
+
+#define SDP_COMMAND_LEN		16
+
+struct sdp_command {
+	u16 cmd;
+	u32 addr;
+	u8 format;
+	u32 cnt;
+	u32 data;
+	u8 rsvd;
+} __packed;
+
+enum sdp_state {
+	SDP_STATE_IDLE,
+	SDP_STATE_RX_DCD_DATA,
+	SDP_STATE_RX_FILE_DATA,
+	SDP_STATE_TX_SEC_CONF,
+	SDP_STATE_TX_SEC_CONF_BUSY,
+	SDP_STATE_TX_REGISTER,
+	SDP_STATE_TX_REGISTER_BUSY,
+	SDP_STATE_TX_STATUS,
+	SDP_STATE_TX_STATUS_BUSY,
+	SDP_STATE_JUMP,
+};
+
+struct f_sdp {
+	struct usb_function		usb_function;
+
+	struct usb_descriptor_header	**function;
+
+	u8				altsetting;
+	enum sdp_state			state;
+	enum sdp_state			next_state;
+	u32				dnl_address;
+	u32				dnl_bytes_remaining;
+	u32				jmp_address;
+	bool				always_send_status;
+	u32				error_status;
+
+	/* EP0 request */
+	struct usb_request		*req;
+
+	/* EP1 IN */
+	struct usb_ep			*in_ep;
+	struct usb_request		*in_req;
+
+	bool				configuration_done;
+};
+
+static struct f_sdp *sdp_func;
+
+static inline struct f_sdp *func_to_sdp(struct usb_function *f)
+{
+	return container_of(f, struct f_sdp, usb_function);
+}
+
+static struct usb_interface_descriptor sdp_intf_runtime = {
+	.bLength =		sizeof(sdp_intf_runtime),
+	.bDescriptorType =	USB_DT_INTERFACE,
+	.bAlternateSetting =	0,
+	.bNumEndpoints =	1,
+	.bInterfaceClass =	USB_CLASS_HID,
+	.bInterfaceSubClass =	0,
+	.bInterfaceProtocol =	0,
+	/* .iInterface = DYNAMIC */
+};
+
+/* HID configuration */
+static struct usb_class_hid_descriptor sdp_hid_desc = {
+	.bLength =		sizeof(sdp_hid_desc),
+	.bDescriptorType =	USB_DT_CS_DEVICE,
+
+	.bcdCDC =		__constant_cpu_to_le16(0x0110),
+	.bCountryCode =		0,
+	.bNumDescriptors =	1,
+
+	.bDescriptorType0	= USB_DT_HID_REPORT,
+	.wDescriptorLength0	= HID_USAGE_PAGE_LEN,
+};
+
+static struct usb_endpoint_descriptor in_desc = {
+	.bLength =		USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType =	USB_DT_ENDPOINT, /*USB_DT_CS_ENDPOINT*/
+
+	.bEndpointAddress =	1 | USB_DIR_IN,
+	.bmAttributes =	USB_ENDPOINT_XFER_INT,
+	.wMaxPacketSize =	64,
+	.bInterval =		1,
+};
+
+static struct usb_descriptor_header *sdp_runtime_descs[] = {
+	(struct usb_descriptor_header *)&sdp_intf_runtime,
+	(struct usb_descriptor_header *)&sdp_hid_desc,
+	(struct usb_descriptor_header *)&in_desc,
+	NULL,
+};
+
+/* This is synchronized with what the SoC implementation reports */
+static struct hid_report sdp_hid_report = {
+	.usage_page = {
+		0x06, 0x00, 0xff, /* Usage Page */
+		0x09, 0x01, /* Usage (Pointer?) */
+		0xa1, 0x01, /* Collection */
+
+		0x85, 0x01, /* Report ID */
+		0x19, 0x01, /* Usage Minimum */
+		0x29, 0x01, /* Usage Maximum */
+		0x15, 0x00, /* Local Minimum */
+		0x26, 0xFF, 0x00, /* Local Maximum? */
+		0x75, 0x08, /* Report Size */
+		0x95, 0x10, /* Report Count */
+		0x91, 0x02, /* Output Data */
+
+		0x85, 0x02, /* Report ID */
+		0x19, 0x01, /* Usage Minimum */
+		0x29, 0x01, /* Usage Maximum */
+		0x15, 0x00, /* Local Minimum */
+		0x26, 0xFF, 0x00, /* Local Maximum? */
+		0x75, 0x80, /* Report Size 128 */
+		0x95, 0x40, /* Report Count */
+		0x91, 0x02, /* Output Data */
+
+		0x85, 0x03, /* Report ID */
+		0x19, 0x01, /* Usage Minimum */
+		0x29, 0x01, /* Usage Maximum */
+		0x15, 0x00, /* Local Minimum */
+		0x26, 0xFF, 0x00, /* Local Maximum? */
+		0x75, 0x08, /* Report Size 8 */
+		0x95, 0x04, /* Report Count */
+		0x81, 0x02, /* Input Data */
+
+		0x85, 0x04, /* Report ID */
+		0x19, 0x01, /* Usage Minimum */
+		0x29, 0x01, /* Usage Maximum */
+		0x15, 0x00, /* Local Minimum */
+		0x26, 0xFF, 0x00, /* Local Maximum? */
+		0x75, 0x08, /* Report Size 8 */
+		0x95, 0x40, /* Report Count */
+		0x81, 0x02, /* Input Data */
+		0xc0
+	},
+};
+
+static const char sdp_name[] = "Serial Downloader Protocol";
+
+/*
+ * static strings, in UTF-8
+ */
+static struct usb_string strings_sdp_generic[] = {
+	[0].s = sdp_name,
+	{  }			/* end of list */
+};
+
+static struct usb_gadget_strings stringtab_sdp_generic = {
+	.language	= 0x0409,	/* en-us */
+	.strings	= strings_sdp_generic,
+};
+
+static struct usb_gadget_strings *sdp_generic_strings[] = {
+	&stringtab_sdp_generic,
+	NULL,
+};
+
+static void sdp_rx_command_complete(struct usb_ep *ep, struct usb_request *req)
+{
+	struct f_sdp *sdp = req->context;
+	int status = req->status;
+	u8 *data = req->buf;
+	u8 report = data[0];
+
+	if (status != 0) {
+		error("Status: %d", status);
+		return;
+	}
+
+	if (report != 1) {
+		error("Unexpected report %d", report);
+		return;
+	}
+
+	struct sdp_command *cmd = req->buf + 1;
+
+	debug("%s: command: %04x, addr: %08x, cnt: %u\n",
+	      __func__, be16_to_cpu(cmd->cmd),
+	      be32_to_cpu(cmd->addr), be32_to_cpu(cmd->cnt));
+
+	switch (be16_to_cpu(cmd->cmd)) {
+	case SDP_READ_REGISTER:
+		sdp->always_send_status = false;
+		sdp->error_status = 0x0;
+
+		sdp->state = SDP_STATE_TX_SEC_CONF;
+		sdp->dnl_address = be32_to_cpu(cmd->addr);
+		sdp->dnl_bytes_remaining = be32_to_cpu(cmd->cnt);
+		sdp->next_state = SDP_STATE_TX_REGISTER;
+		printf("Reading %d registers at 0x%08x... ",
+		       sdp->dnl_bytes_remaining, sdp->dnl_address);
+		break;
+	case SDP_WRITE_FILE:
+		sdp->always_send_status = true;
+		sdp->error_status = SDP_WRITE_FILE_COMPLETE;
+
+		sdp->state = SDP_STATE_RX_FILE_DATA;
+		sdp->dnl_address = be32_to_cpu(cmd->addr);
+		sdp->dnl_bytes_remaining = be32_to_cpu(cmd->cnt);
+		sdp->next_state = SDP_STATE_IDLE;
+
+		printf("Downloading file of size %d to 0x%08x... ",
+		       sdp->dnl_bytes_remaining, sdp->dnl_address);
+
+		break;
+	case SDP_ERROR_STATUS:
+		sdp->always_send_status = true;
+		sdp->error_status = 0;
+
+		sdp->state = SDP_STATE_TX_SEC_CONF;
+		sdp->next_state = SDP_STATE_IDLE;
+		break;
+	case SDP_DCD_WRITE:
+		sdp->always_send_status = true;
+		sdp->error_status = SDP_WRITE_REGISTER_COMPLETE;
+
+		sdp->state = SDP_STATE_RX_DCD_DATA;
+		sdp->dnl_bytes_remaining = be32_to_cpu(cmd->cnt);
+		sdp->next_state = SDP_STATE_IDLE;
+		break;
+	case SDP_JUMP_ADDRESS:
+		sdp->always_send_status = false;
+		sdp->error_status = 0;
+
+		sdp->jmp_address = be32_to_cpu(cmd->addr);
+		sdp->state = SDP_STATE_TX_SEC_CONF;
+		sdp->next_state = SDP_STATE_JUMP;
+		break;
+	case SDP_SKIP_DCD_HEADER:
+		sdp->always_send_status = true;
+		sdp->error_status = SDP_SKIP_DCD_HEADER_COMPLETE;
+
+		/* Ignore command, DCD not supported anyway */
+		sdp->state = SDP_STATE_TX_SEC_CONF;
+		sdp->next_state = SDP_STATE_IDLE;
+		break;
+	default:
+		error("Unknown command: %04x\n", be16_to_cpu(cmd->cmd));
+	}
+}
+
+static void sdp_rx_data_complete(struct usb_ep *ep, struct usb_request *req)
+{
+	struct f_sdp *sdp = req->context;
+	int status = req->status;
+	u8 *data = req->buf;
+	u8 report = data[0];
+	int datalen = req->length - 1;
+
+	if (status != 0) {
+		error("Status: %d", status);
+		return;
+	}
+
+	if (report != 2) {
+		error("Unexpected report %d", report);
+		return;
+	}
+
+	if (sdp->dnl_bytes_remaining < datalen) {
+		/*
+		 * Some USB stacks require to send a complete buffer as
+		 * specified in the HID descriptor. This leads to longer
+		 * transfers than the file length, no problem for us.
+		 */
+		sdp->dnl_bytes_remaining = 0;
+	} else {
+		sdp->dnl_bytes_remaining -= datalen;
+	}
+
+	if (sdp->state == SDP_STATE_RX_FILE_DATA) {
+		memcpy((void *)sdp->dnl_address, req->buf + 1, datalen);
+		sdp->dnl_address += datalen;
+	}
+
+	if (sdp->dnl_bytes_remaining)
+		return;
+
+	printf("done\n");
+
+	switch (sdp->state) {
+	case SDP_STATE_RX_FILE_DATA:
+		sdp->state = SDP_STATE_TX_SEC_CONF;
+		break;
+	case SDP_STATE_RX_DCD_DATA:
+		sdp->state = SDP_STATE_TX_SEC_CONF;
+		break;
+	default:
+		error("Invalid state: %d", sdp->state);
+	}
+}
+
+static void sdp_tx_complete(struct usb_ep *ep, struct usb_request *req)
+{
+	struct f_sdp *sdp = req->context;
+	int status = req->status;
+
+	if (status != 0) {
+		error("Status: %d", status);
+		return;
+	}
+
+	switch (sdp->state) {
+	case SDP_STATE_TX_SEC_CONF_BUSY:
+		/* Not all commands require status report */
+		if (sdp->always_send_status || sdp->error_status)
+			sdp->state = SDP_STATE_TX_STATUS;
+		else
+			sdp->state = sdp->next_state;
+
+		break;
+	case SDP_STATE_TX_STATUS_BUSY:
+		sdp->state = sdp->next_state;
+		break;
+	case SDP_STATE_TX_REGISTER_BUSY:
+		if (sdp->dnl_bytes_remaining)
+			sdp->state = SDP_STATE_TX_REGISTER;
+		else
+			sdp->state = SDP_STATE_IDLE;
+		break;
+	default:
+		error("Wrong State: %d", sdp->state);
+		sdp->state = SDP_STATE_IDLE;
+		break;
+	}
+	debug("%s complete --> %d, %d/%d\n", ep->name,
+	      status, req->actual, req->length);
+}
+
+static int sdp_setup(struct usb_function *f, const struct usb_ctrlrequest *ctrl)
+{
+	struct usb_gadget *gadget = f->config->cdev->gadget;
+	struct usb_request *req = f->config->cdev->req;
+	struct f_sdp *sdp = f->config->cdev->req->context;
+	u16 len = le16_to_cpu(ctrl->wLength);
+	u16 w_value = le16_to_cpu(ctrl->wValue);
+	int value = 0;
+	u8 req_type = ctrl->bRequestType & USB_TYPE_MASK;
+
+	debug("w_value: 0x%04x len: 0x%04x\n", w_value, len);
+	debug("req_type: 0x%02x ctrl->bRequest: 0x%02x sdp->state: %d\n",
+	      req_type, ctrl->bRequest, sdp->state);
+
+	if (req_type == USB_TYPE_STANDARD) {
+		if (ctrl->bRequest == USB_REQ_GET_DESCRIPTOR) {
+			/* Send HID report descriptor */
+			value = min(len, (u16) sizeof(sdp_hid_report));
+			memcpy(req->buf, &sdp_hid_report, value);
+			sdp->configuration_done = true;
+		}
+	}
+
+	if (req_type == USB_TYPE_CLASS) {
+		int report = w_value & HID_REPORT_ID_MASK;
+
+		/* HID (SDP) request */
+		switch (ctrl->bRequest) {
+		case HID_REQ_SET_REPORT:
+			switch (report) {
+			case 1:
+				value = SDP_COMMAND_LEN + 1;
+				req->complete = sdp_rx_command_complete;
+				break;
+			case 2:
+				value = len;
+				req->complete = sdp_rx_data_complete;
+				break;
+			}
+		}
+	}
+
+	if (value >= 0) {
+		req->length = value;
+		req->zero = value < len;
+		value = usb_ep_queue(gadget->ep0, req, 0);
+		if (value < 0) {
+			debug("ep_queue --> %d\n", value);
+			req->status = 0;
+		}
+	}
+
+	return value;
+}
+
+static int sdp_bind(struct usb_configuration *c, struct usb_function *f)
+{
+	struct usb_gadget *gadget = c->cdev->gadget;
+	struct usb_composite_dev *cdev = c->cdev;
+	struct f_sdp *sdp = func_to_sdp(f);
+	int rv = 0, id;
+
+	id = usb_interface_id(c, f);
+	if (id < 0)
+		return id;
+	sdp_intf_runtime.bInterfaceNumber = id;
+
+	struct usb_ep *ep;
+
+	/* allocate instance-specific endpoints */
+	ep = usb_ep_autoconfig(gadget, &in_desc);
+	if (!ep) {
+		rv = -ENODEV;
+		goto error;
+	}
+
+	sdp->in_ep = ep; /* Store IN EP for enabling @ setup */
+
+	cdev->req->context = sdp;
+
+error:
+	return rv;
+}
+
+static void sdp_unbind(struct usb_configuration *c, struct usb_function *f)
+{
+	free(sdp_func);
+	sdp_func = NULL;
+}
+
+static struct usb_request *alloc_ep_req(struct usb_ep *ep, unsigned length)
+{
+	struct usb_request *req;
+
+	req = usb_ep_alloc_request(ep, 0);
+	if (!req)
+		return req;
+
+	req->length = length;
+	req->buf = memalign(CONFIG_SYS_CACHELINE_SIZE, length);
+	if (!req->buf) {
+		usb_ep_free_request(ep, req);
+		req = NULL;
+	}
+
+	return req;
+}
+
+
+static struct usb_request *sdp_start_ep(struct usb_ep *ep)
+{
+	struct usb_request *req;
+
+	req = alloc_ep_req(ep, 64);
+	debug("%s: ep:%p req:%p\n", __func__, ep, req);
+
+	if (!req)
+		return NULL;
+
+	memset(req->buf, 0, req->length);
+	req->complete = sdp_tx_complete;
+
+	return req;
+}
+static int sdp_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
+{
+	struct f_sdp *sdp = func_to_sdp(f);
+	struct usb_composite_dev *cdev = f->config->cdev;
+	int result;
+
+	debug("%s: intf: %d alt: %d\n", __func__, intf, alt);
+
+	result = usb_ep_enable(sdp->in_ep, &in_desc);
+	if (result)
+		return result;
+	sdp->in_req = sdp_start_ep(sdp->in_ep);
+	sdp->in_req->context = sdp;
+
+	sdp->in_ep->driver_data = cdev; /* claim */
+
+	sdp->altsetting = alt;
+	sdp->state = SDP_STATE_IDLE;
+
+	return 0;
+}
+
+static int sdp_get_alt(struct usb_function *f, unsigned intf)
+{
+	struct f_sdp *sdp = func_to_sdp(f);
+
+	return sdp->altsetting;
+}
+
+static void sdp_disable(struct usb_function *f)
+{
+	struct f_sdp *sdp = func_to_sdp(f);
+
+	usb_ep_disable(sdp->in_ep);
+
+	if (sdp->in_req) {
+		free(sdp->in_req);
+		sdp->in_req = NULL;
+	}
+}
+
+static int sdp_bind_config(struct usb_configuration *c)
+{
+	int status;
+
+	if (!sdp_func) {
+		sdp_func = memalign(CONFIG_SYS_CACHELINE_SIZE, sizeof(*sdp_func));
+		if (!sdp_func)
+			return -ENOMEM;
+	}
+
+	memset(sdp_func, 0, sizeof(*sdp_func));
+
+	sdp_func->usb_function.name = "sdp";
+	sdp_func->usb_function.hs_descriptors = sdp_runtime_descs;
+	sdp_func->usb_function.descriptors = sdp_runtime_descs;
+	sdp_func->usb_function.bind = sdp_bind;
+	sdp_func->usb_function.unbind = sdp_unbind;
+	sdp_func->usb_function.set_alt = sdp_set_alt;
+	sdp_func->usb_function.get_alt = sdp_get_alt;
+	sdp_func->usb_function.disable = sdp_disable;
+	sdp_func->usb_function.strings = sdp_generic_strings;
+	sdp_func->usb_function.setup = sdp_setup;
+
+	status = usb_add_function(c, &sdp_func->usb_function);
+
+	return status;
+}
+
+int sdp_init(int controller_index)
+{
+	printf("SDP: initialize...\n");
+	while (!sdp_func->configuration_done) {
+		if (ctrlc()) {
+			puts("\rCTRL+C - Operation aborted.\n");
+			return 1;
+		}
+		usb_gadget_handle_interrupts(controller_index);
+	}
+
+	return 0;
+}
+
+static u32 sdp_jump_imxheader(void *address)
+{
+	flash_header_v2_t *headerv2 = address;
+	ulong (*entry)(void);
+
+	if (headerv2->header.tag != IVT_HEADER_TAG) {
+		printf("Header Tag is not an IMX image\n");
+		return SDP_ERROR_IMXHEADER;
+	}
+
+	printf("Jumping to 0x%08x\n", headerv2->entry);
+	entry = (void *)headerv2->entry;
+	entry();
+
+	/* The image probably never returns hence we won't reach that point */
+	return 0;
+}
+
+static void sdp_handle_in_ep(void)
+{
+	u8 *data = sdp_func->in_req->buf;
+	u32 status;
+	int datalen;
+
+	switch (sdp_func->state) {
+	case SDP_STATE_TX_SEC_CONF:
+		debug("Report 3: HAB security\n");
+		data[0] = 3;
+
+		status = SDP_SECURITY_OPEN;
+		memcpy(&data[1], &status, 4);
+		sdp_func->in_req->length = 5;
+		usb_ep_queue(sdp_func->in_ep, sdp_func->in_req, 0);
+		sdp_func->state = SDP_STATE_TX_SEC_CONF_BUSY;
+		break;
+
+	case SDP_STATE_TX_STATUS:
+		debug("Report 4: Status\n");
+		data[0] = 4;
+
+		memcpy(&data[1], &sdp_func->error_status, 4);
+		sdp_func->in_req->length = 65;
+		usb_ep_queue(sdp_func->in_ep, sdp_func->in_req, 0);
+		sdp_func->state = SDP_STATE_TX_STATUS_BUSY;
+		break;
+	case SDP_STATE_TX_REGISTER:
+		debug("Report 4: Register Values\n");
+		data[0] = 4;
+
+		datalen = sdp_func->dnl_bytes_remaining;
+
+		if (datalen > 64)
+			datalen = 64;
+
+		memcpy(&data[1], (void *)sdp_func->dnl_address, datalen);
+		sdp_func->in_req->length = 65;
+
+		sdp_func->dnl_bytes_remaining -= datalen;
+		sdp_func->dnl_address += datalen;
+
+		usb_ep_queue(sdp_func->in_ep, sdp_func->in_req, 0);
+		sdp_func->state = SDP_STATE_TX_REGISTER_BUSY;
+		break;
+	case SDP_STATE_JUMP:
+		printf("Checking imxheader at 0x%08x\n", f_sdp->jmp_address);
+		status = sdp_jump_imxheader((void *)f_sdp->jmp_address);
+
+		sdp_func->next_state = SDP_STATE_IDLE;
+		sdp_func->error_status = status;
+
+		/* Only send Report 4 if there was an error */
+		if (status)
+			sdp_func->state = SDP_STATE_TX_STATUS;
+		else
+			sdp_func->state = SDP_STATE_IDLE;
+		break;
+	default:
+		break;
+	};
+}
+
+void sdp_handle(int controller_index)
+{
+	printf("SDP: handle requests...\n");
+	while (1) {
+		if (ctrlc()) {
+			puts("\rCTRL+C - Operation aborted.\n");
+			return;
+		}
+
+		usb_gadget_handle_interrupts(controller_index);
+
+		sdp_handle_in_ep();
+	}
+}
+
+int sdp_add(struct usb_configuration *c)
+{
+	int id;
+
+	id = usb_string_id(c->cdev);
+	if (id < 0)
+		return id;
+	strings_sdp_generic[0].id = id;
+	sdp_intf_runtime.iInterface = id;
+
+	debug("%s: cdev: %p gadget: %p gadget->ep0: %p\n", __func__,
+	      c->cdev, c->cdev->gadget, c->cdev->gadget->ep0);
+
+	return sdp_bind_config(c);
+}
+
+DECLARE_GADGET_BIND_CALLBACK(usb_dnl_sdp, sdp_add);
diff --git a/include/sdp.h b/include/sdp.h
new file mode 100644
index 0000000000..f476bab8f1
--- /dev/null
+++ b/include/sdp.h
@@ -0,0 +1,16 @@
+/*
+ * sdp.h - Serial Download Protocol
+ *
+ * Copyright (C) 2017 Toradex
+ * Author: Stefan Agner <stefan.agner@toradex.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef __SDP_H_
+#define __SDP_H_
+
+int sdp_init(int controller_index);
+void sdp_handle(int controller_index);
+
+#endif /* __SDP_H_ */