usb: gadget: make sure each gadget is using same index for Product, Serial,…

The index in usb_string array is defined by the gadget. The gadget can
choose which index entry it assigns for the serial number and which the
product name. The gadget has just to ensure that the descriptor contains
the proper string id which is assigned by composite.
If the composite layer knows the index of the "default" information
which will be overwritten by module parameters, it can be used later to
overwrite it.

Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/acm_ms.c

@@ -90,14 +90,12 @@ static const struct usb_descriptor_header *otg_desc[] = {
 
 /* string IDs are assigned dynamically */
 
-#define STRING_MANUFACTURER_IDX		0
-#define STRING_PRODUCT_IDX		1
-
 static char manufacturer[50];
 
 static struct usb_string strings_dev[] = {
-	[STRING_MANUFACTURER_IDX].s = manufacturer,
-	[STRING_PRODUCT_IDX].s = DRIVER_DESC,
+	[USB_GADGET_MANUFACTURER_IDX].s = manufacturer,
+	[USB_GADGET_PRODUCT_IDX].s = DRIVER_DESC,
+	[USB_GADGET_SERIAL_IDX].s = "",
 	{  } /* end of list */
 };
 
@@ -196,8 +194,8 @@ static int __init acm_ms_bind(struct usb_composite_dev *cdev)
 	status = usb_string_ids_tab(cdev, strings_dev);
 	if (status < 0)
 		goto fail1;
-	device_desc.iManufacturer = strings_dev[STRING_MANUFACTURER_IDX].id;
-	device_desc.iProduct = strings_dev[STRING_PRODUCT_IDX].id;
+	device_desc.iManufacturer = strings_dev[USB_GADGET_MANUFACTURER_IDX].id;
+	device_desc.iProduct = strings_dev[USB_GADGET_PRODUCT_IDX].id;
 
 	/* register our configuration */
 	status = usb_add_config(cdev, &acm_ms_config_driver, acm_ms_do_config);

drivers/usb/gadget/audio.c

@@ -33,14 +33,12 @@ USB_GADGET_COMPOSITE_OPTIONS();
 
 /* string IDs are assigned dynamically */
 
-#define STRING_MANUFACTURER_IDX		0
-#define STRING_PRODUCT_IDX		1
-
 static char manufacturer[50];
 
 static struct usb_string strings_dev[] = {
-	[STRING_MANUFACTURER_IDX].s = manufacturer,
-	[STRING_PRODUCT_IDX].s = DRIVER_DESC,
+	[USB_GADGET_MANUFACTURER_IDX].s = manufacturer,
+	[USB_GADGET_PRODUCT_IDX].s = DRIVER_DESC,
+	[USB_GADGET_SERIAL_IDX].s = "",
 	{  } /* end of list */
 };
 
@@ -170,8 +168,8 @@ static int __init audio_bind(struct usb_composite_dev *cdev)
 	status = usb_string_ids_tab(cdev, strings_dev);
 	if (status < 0)
 		goto fail;
-	device_desc.iManufacturer = strings_dev[STRING_MANUFACTURER_IDX].id;
-	device_desc.iProduct = strings_dev[STRING_PRODUCT_IDX].id;
+	device_desc.iManufacturer = strings_dev[USB_GADGET_MANUFACTURER_IDX].id;
+	device_desc.iProduct = strings_dev[USB_GADGET_PRODUCT_IDX].id;
 
 	status = usb_add_config(cdev, &audio_config_driver, audio_do_config);
 	if (status < 0)

drivers/usb/gadget/cdc2.c

@@ -90,15 +90,12 @@ static const struct usb_descriptor_header *otg_desc[] = {
 
 
 /* string IDs are assigned dynamically */
-
-#define STRING_MANUFACTURER_IDX		0
-#define STRING_PRODUCT_IDX		1
-
 static char manufacturer[50];
 
 static struct usb_string strings_dev[] = {
-	[STRING_MANUFACTURER_IDX].s = manufacturer,
-	[STRING_PRODUCT_IDX].s = DRIVER_DESC,
+	[USB_GADGET_MANUFACTURER_IDX].s = manufacturer,
+	[USB_GADGET_PRODUCT_IDX].s = DRIVER_DESC,
+	[USB_GADGET_SERIAL_IDX].s = "",
 	{  } /* end of list */
 };
 
@@ -197,8 +194,8 @@ static int __init cdc_bind(struct usb_composite_dev *cdev)
 	status = usb_string_ids_tab(cdev, strings_dev);
 	if (status < 0)
 		goto fail1;
-	device_desc.iManufacturer = strings_dev[STRING_MANUFACTURER_IDX].id;
-	device_desc.iProduct = strings_dev[STRING_PRODUCT_IDX].id;
+	device_desc.iManufacturer = strings_dev[USB_GADGET_MANUFACTURER_IDX].id;
+	device_desc.iProduct = strings_dev[USB_GADGET_PRODUCT_IDX].id;
 
 	/* register our configuration */
 	status = usb_add_config(cdev, &cdc_config_driver, cdc_do_config);

drivers/usb/gadget/ether.c

@@ -193,17 +193,13 @@ static const struct usb_descriptor_header *otg_desc[] = {
 	NULL,
 };
 
-
 /* string IDs are assigned dynamically */
-
-#define STRING_MANUFACTURER_IDX		0
-#define STRING_PRODUCT_IDX		1
-
 static char manufacturer[50];
 
 static struct usb_string strings_dev[] = {
-	[STRING_MANUFACTURER_IDX].s = manufacturer,
-	[STRING_PRODUCT_IDX].s = PREFIX DRIVER_DESC,
+	[USB_GADGET_MANUFACTURER_IDX].s = manufacturer,
+	[USB_GADGET_PRODUCT_IDX].s = PREFIX DRIVER_DESC,
+	[USB_GADGET_SERIAL_IDX].s = "",
 	{  } /* end of list */
 };
 
@@ -349,8 +345,8 @@ static int __init eth_bind(struct usb_composite_dev *cdev)
 	status = usb_string_ids_tab(cdev, strings_dev);
 	if (status < 0)
 		goto fail;
-	device_desc.iManufacturer = strings_dev[STRING_MANUFACTURER_IDX].id;
-	device_desc.iProduct = strings_dev[STRING_PRODUCT_IDX].id;
+	device_desc.iManufacturer = strings_dev[USB_GADGET_MANUFACTURER_IDX].id;
+	device_desc.iProduct = strings_dev[USB_GADGET_PRODUCT_IDX].id;
 
 	/* register our configuration(s); RNDIS first, if it's used */
 	if (has_rndis()) {

drivers/usb/gadget/g_ffs.c

@@ -116,6 +116,9 @@ static const struct usb_descriptor_header *gfs_otg_desc[] = {
 
 /* String IDs are assigned dynamically */
 static struct usb_string gfs_strings[] = {
+	[USB_GADGET_MANUFACTURER_IDX].s = "",
+	[USB_GADGET_PRODUCT_IDX].s = "",
+	[USB_GADGET_SERIAL_IDX].s = "",
 #ifdef CONFIG_USB_FUNCTIONFS_RNDIS
 	{ .s = "FunctionFS + RNDIS" },
 #endif
@@ -369,9 +372,10 @@ static int gfs_bind(struct usb_composite_dev *cdev)
 
 	for (i = 0; i < ARRAY_SIZE(gfs_configurations); ++i) {
 		struct gfs_configuration *c = gfs_configurations + i;
+		int sid = USB_GADGET_FIRST_AVAIL_IDX + i;
 
-		c->c.label			= gfs_strings[i].s;
-		c->c.iConfiguration		= gfs_strings[i].id;
+		c->c.label			= gfs_strings[sid].s;
+		c->c.iConfiguration		= gfs_strings[sid].id;
 		c->c.bConfigurationValue	= 1 + i;
 		c->c.bmAttributes		= USB_CONFIG_ATT_SELFPOWER;
 

drivers/usb/gadget/gmidi.c

@@ -84,9 +84,7 @@ MODULE_PARM_DESC(out_ports, "Number of MIDI output ports");
 
 /* string IDs are assigned dynamically */
 
-#define STRING_MANUFACTURER_IDX		0
-#define STRING_PRODUCT_IDX		1
-#define STRING_DESCRIPTION_IDX		2
+#define STRING_DESCRIPTION_IDX		USB_GADGET_FIRST_AVAIL_IDX
 
 static struct usb_device_descriptor device_desc = {
 	.bLength =		USB_DT_DEVICE_SIZE,
@@ -101,8 +99,9 @@ static struct usb_device_descriptor device_desc = {
 };
 
 static struct usb_string strings_dev[] = {
-	[STRING_MANUFACTURER_IDX].s	= "Grey Innovation",
-	[STRING_PRODUCT_IDX].s		= "MIDI Gadget",
+	[USB_GADGET_MANUFACTURER_IDX].s	= "Grey Innovation",
+	[USB_GADGET_PRODUCT_IDX].s	= "MIDI Gadget",
+	[USB_GADGET_SERIAL_IDX].s	= "",
 	[STRING_DESCRIPTION_IDX].s	= "MIDI",
 	{  } /* end of list */
 };
@@ -145,8 +144,8 @@ static int __init midi_bind(struct usb_composite_dev *cdev)
 	status = usb_string_ids_tab(cdev, strings_dev);
 	if (status < 0)
 		return status;
-	device_desc.iManufacturer = strings_dev[STRING_MANUFACTURER_IDX].id;
-	device_desc.iProduct = strings_dev[STRING_PRODUCT_IDX].id;
+	device_desc.iManufacturer = strings_dev[USB_GADGET_MANUFACTURER_IDX].id;
+	device_desc.iProduct = strings_dev[USB_GADGET_PRODUCT_IDX].id;
 	midi_config.iConfiguration = strings_dev[STRING_DESCRIPTION_IDX].id;
 
 	gcnum = usb_gadget_controller_number(gadget);

drivers/usb/gadget/hid.c

@@ -91,15 +91,12 @@ static const struct usb_descriptor_header *otg_desc[] = {
 
 
 /* string IDs are assigned dynamically */
-
-#define STRING_MANUFACTURER_IDX		0
-#define STRING_PRODUCT_IDX		1
-
 static char manufacturer[50];
 
 static struct usb_string strings_dev[] = {
-	[STRING_MANUFACTURER_IDX].s = manufacturer,
-	[STRING_PRODUCT_IDX].s = DRIVER_DESC,
+	[USB_GADGET_MANUFACTURER_IDX].s = manufacturer,
+	[USB_GADGET_PRODUCT_IDX].s = DRIVER_DESC,
+	[USB_GADGET_SERIAL_IDX].s = "",
 	{  } /* end of list */
 };
 
@@ -181,8 +178,8 @@ static int __init hid_bind(struct usb_composite_dev *cdev)
 	status = usb_string_ids_tab(cdev, strings_dev);
 	if (status < 0)
 		return status;
-	device_desc.iManufacturer = strings_dev[STRING_MANUFACTURER_IDX].id;
-	device_desc.iProduct = strings_dev[STRING_PRODUCT_IDX].id;
+	device_desc.iManufacturer = strings_dev[USB_GADGET_MANUFACTURER_IDX].id;
+	device_desc.iProduct = strings_dev[USB_GADGET_PRODUCT_IDX].id;
 
 	/* register our configuration */
 	status = usb_add_config(cdev, &config_driver, do_config);

drivers/usb/gadget/multi.c

@@ -109,21 +109,16 @@ static const struct usb_descriptor_header *otg_desc[] = {
 
 
 enum {
-#ifdef CONFIG_USB_G_MULTI_RNDIS
-	MULTI_STRING_RNDIS_CONFIG_IDX,
-#endif
-#ifdef CONFIG_USB_G_MULTI_CDC
+	MULTI_STRING_RNDIS_CONFIG_IDX = USB_GADGET_FIRST_AVAIL_IDX,
 	MULTI_STRING_CDC_CONFIG_IDX,
-#endif
 };
 
 static struct usb_string strings_dev[] = {
-#ifdef CONFIG_USB_G_MULTI_RNDIS
+	[USB_GADGET_MANUFACTURER_IDX].s = "",
+	[USB_GADGET_PRODUCT_IDX].s = "",
+	[USB_GADGET_SERIAL_IDX].s = "",
 	[MULTI_STRING_RNDIS_CONFIG_IDX].s = "Multifunction with RNDIS",
-#endif
-#ifdef CONFIG_USB_G_MULTI_CDC
 	[MULTI_STRING_CDC_CONFIG_IDX].s   = "Multifunction with CDC ECM",
-#endif
 	{  } /* end of list */
 };
 

drivers/usb/gadget/ncm.c

@@ -97,15 +97,12 @@ static const struct usb_descriptor_header *otg_desc[] = {
 
 
 /* string IDs are assigned dynamically */
-
-#define STRING_MANUFACTURER_IDX		0
-#define STRING_PRODUCT_IDX		1
-
 static char manufacturer[50];
 
 static struct usb_string strings_dev[] = {
-	[STRING_MANUFACTURER_IDX].s = manufacturer,
-	[STRING_PRODUCT_IDX].s = DRIVER_DESC,
+	[USB_GADGET_MANUFACTURER_IDX].s = manufacturer,
+	[USB_GADGET_PRODUCT_IDX].s = DRIVER_DESC,
+	[USB_GADGET_SERIAL_IDX].s = "",
 	{  } /* end of list */
 };
 
@@ -184,8 +181,8 @@ static int __init gncm_bind(struct usb_composite_dev *cdev)
 	status = usb_string_ids_tab(cdev, strings_dev);
 	if (status < 0)
 		goto fail;
-	device_desc.iManufacturer = strings_dev[STRING_MANUFACTURER_IDX].id;
-	device_desc.iProduct = strings_dev[STRING_PRODUCT_IDX].id;
+	device_desc.iManufacturer = strings_dev[USB_GADGET_MANUFACTURER_IDX].id;
+	device_desc.iProduct = strings_dev[USB_GADGET_PRODUCT_IDX].id;
 
 	status = usb_add_config(cdev, &ncm_config_driver,
 				ncm_do_config);

drivers/usb/gadget/nokia.c

@@ -56,17 +56,16 @@ USB_GADGET_COMPOSITE_OPTIONS();
 
 /* string IDs are assigned dynamically */
 
-#define STRING_MANUFACTURER_IDX		0
-#define STRING_PRODUCT_IDX		1
-#define STRING_DESCRIPTION_IDX		2
+#define STRING_DESCRIPTION_IDX		USB_GADGET_FIRST_AVAIL_IDX
 
 static char manufacturer_nokia[] = "Nokia";
 static const char product_nokia[] = NOKIA_LONG_NAME;
 static const char description_nokia[] = "PC-Suite Configuration";
 
 static struct usb_string strings_dev[] = {
-	[STRING_MANUFACTURER_IDX].s = manufacturer_nokia,
-	[STRING_PRODUCT_IDX].s = NOKIA_LONG_NAME,
+	[USB_GADGET_MANUFACTURER_IDX].s = manufacturer_nokia,
+	[USB_GADGET_PRODUCT_IDX].s = NOKIA_LONG_NAME,
+	[USB_GADGET_SERIAL_IDX].s = "",
 	[STRING_DESCRIPTION_IDX].s = description_nokia,
 	{  } /* end of list */
 };
@@ -168,8 +167,8 @@ static int __init nokia_bind(struct usb_composite_dev *cdev)
 	status = usb_string_ids_tab(cdev, strings_dev);
 	if (status < 0)
 		goto err_usb;
-	device_desc.iManufacturer = strings_dev[STRING_MANUFACTURER_IDX].id;
-	device_desc.iProduct = strings_dev[STRING_PRODUCT_IDX].id;
+	device_desc.iManufacturer = strings_dev[USB_GADGET_MANUFACTURER_IDX].id;
+	device_desc.iProduct = strings_dev[USB_GADGET_PRODUCT_IDX].id;
 	status = strings_dev[STRING_DESCRIPTION_IDX].id;
 	nokia_config_500ma_driver.iConfiguration = status;
 	nokia_config_100ma_driver.iConfiguration = status;

drivers/usb/gadget/printer.c

@@ -139,10 +139,6 @@ module_param(qlen, uint, S_IRUGO|S_IWUSR);
  * descriptors are built on demand.
  */
 
-#define STRING_MANUFACTURER		0
-#define STRING_PRODUCT			1
-#define STRING_SERIALNUM		2
-
 /* holds our biggest descriptor */
 #define USB_DESC_BUFSIZE		256
 #define USB_BUFSIZE			8192
@@ -250,9 +246,9 @@ static char				pnp_string [1024] =
 
 /* static strings, in UTF-8 */
 static struct usb_string		strings [] = {
-	[STRING_MANUFACTURER].s = manufacturer,
-	[STRING_PRODUCT].s = product_desc,
-	[STRING_SERIALNUM].s =	serial_num,
+	[USB_GADGET_MANUFACTURER_IDX].s = manufacturer,
+	[USB_GADGET_PRODUCT_IDX].s = product_desc,
+	[USB_GADGET_SERIAL_IDX].s =	serial_num,
 	{  }		/* end of list */
 };
 
@@ -1261,9 +1257,9 @@ static int __init printer_bind(struct usb_composite_dev *cdev)
 	ret = usb_string_ids_tab(cdev, strings);
 	if (ret < 0)
 		return ret;
-	device_desc.iManufacturer = strings[STRING_MANUFACTURER].id;
-	device_desc.iProduct = strings[STRING_PRODUCT].id;
-	device_desc.iSerialNumber = strings[STRING_SERIALNUM].id;
+	device_desc.iManufacturer = strings[USB_GADGET_MANUFACTURER_IDX].id;
+	device_desc.iProduct = strings[USB_GADGET_PRODUCT_IDX].id;
+	device_desc.iSerialNumber = strings[USB_GADGET_SERIAL_IDX].id;
 
 	ret = usb_add_config(cdev, &printer_cfg_driver, printer_bind_config);
 	if (ret)

drivers/usb/gadget/serial.c

@@ -59,15 +59,14 @@ USB_GADGET_COMPOSITE_OPTIONS();
 
 /* string IDs are assigned dynamically */
 
-#define STRING_MANUFACTURER_IDX		0
-#define STRING_PRODUCT_IDX		1
-#define STRING_DESCRIPTION_IDX		2
+#define STRING_DESCRIPTION_IDX		USB_GADGET_FIRST_AVAIL_IDX
 
 static char manufacturer[50];
 
 static struct usb_string strings_dev[] = {
-	[STRING_MANUFACTURER_IDX].s = manufacturer,
-	[STRING_PRODUCT_IDX].s = GS_VERSION_NAME,
+	[USB_GADGET_MANUFACTURER_IDX].s = manufacturer,
+	[USB_GADGET_PRODUCT_IDX].s = GS_VERSION_NAME,
+	[USB_GADGET_SERIAL_IDX].s = "",
 	[STRING_DESCRIPTION_IDX].s = NULL /* updated; f(use_acm) */,
 	{  } /* end of list */
 };
@@ -179,8 +178,8 @@ static int __init gs_bind(struct usb_composite_dev *cdev)
 	status = usb_string_ids_tab(cdev, strings_dev);
 	if (status < 0)
 		goto fail;
-	device_desc.iManufacturer = strings_dev[STRING_MANUFACTURER_IDX].id;
-	device_desc.iProduct = strings_dev[STRING_PRODUCT_IDX].id;
+	device_desc.iManufacturer = strings_dev[USB_GADGET_MANUFACTURER_IDX].id;
+	device_desc.iProduct = strings_dev[USB_GADGET_PRODUCT_IDX].id;
 	status = strings_dev[STRING_DESCRIPTION_IDX].id;
 	serial_config_driver.iConfiguration = status;
 

drivers/usb/gadget/tcm_usb_gadget.c

@@ -2210,9 +2210,9 @@ static struct usb_device_descriptor usbg_device_desc = {
 };
 
 static struct usb_string	usbg_us_strings[] = {
-	[USB_G_STR_MANUFACTOR].s	= "Target Manufactor",
-	[USB_G_STR_PRODUCT].s		= "Target Product",
-	[USB_G_STR_SERIAL].s		= "000000000001",
+	[USB_GADGET_MANUFACTURER_IDX].s	= "Target Manufactor",
+	[USB_GADGET_PRODUCT_IDX].s	= "Target Product",
+	[USB_GADGET_SERIAL_IDX].s	= "000000000001",
 	[USB_G_STR_CONFIG].s		= "default config",
 	[USB_G_STR_INT_UAS].s		= "USB Attached SCSI",
 	[USB_G_STR_INT_BBB].s		= "Bulk Only Transport",
@@ -2431,9 +2431,10 @@ static int usb_target_bind(struct usb_composite_dev *cdev)
 		return ret;
 
 	usbg_device_desc.iManufacturer =
-		usbg_us_strings[USB_G_STR_MANUFACTOR].id;
-	usbg_device_desc.iProduct = usbg_us_strings[USB_G_STR_PRODUCT].id;
-	usbg_device_desc.iSerialNumber = usbg_us_strings[USB_G_STR_SERIAL].id;
+		usbg_us_strings[USB_GADGET_MANUFACTURER_IDX].id;
+	usbg_device_desc.iProduct = usbg_us_strings[USB_GADGET_PRODUCT_IDX].id;
+	usbg_device_desc.iSerialNumber =
+		usbg_us_strings[USB_GADGET_SERIAL_IDX].id;
 	usbg_config_driver.iConfiguration =
 		usbg_us_strings[USB_G_STR_CONFIG].id;
 

drivers/usb/gadget/tcm_usb_gadget.h

@@ -17,10 +17,7 @@
 #define UASP_SS_EP_COMP_NUM_STREAMS (1 << UASP_SS_EP_COMP_LOG_STREAMS)
 
 enum {
-	USB_G_STR_MANUFACTOR,
-	USB_G_STR_PRODUCT,
-	USB_G_STR_SERIAL,
-	USB_G_STR_CONFIG,
+	USB_G_STR_CONFIG = USB_GADGET_FIRST_AVAIL_IDX,
 	USB_G_STR_INT_UAS,
 	USB_G_STR_INT_BBB,
 };

drivers/usb/gadget/webcam.c

@@ -45,13 +45,12 @@ static char webcam_config_label[] = "Video";
 
 /* string IDs are assigned dynamically */
 
-#define STRING_MANUFACTURER_IDX		0
-#define STRING_PRODUCT_IDX		1
-#define STRING_DESCRIPTION_IDX		2
+#define STRING_DESCRIPTION_IDX		USB_GADGET_FIRST_AVAIL_IDX
 
 static struct usb_string webcam_strings[] = {
-	[STRING_MANUFACTURER_IDX].s = webcam_vendor_label,
-	[STRING_PRODUCT_IDX].s = webcam_product_label,
+	[USB_GADGET_MANUFACTURER_IDX].s = webcam_vendor_label,
+	[USB_GADGET_PRODUCT_IDX].s = webcam_product_label,
+	[USB_GADGET_SERIAL_IDX].s = "",
 	[STRING_DESCRIPTION_IDX].s = webcam_config_label,
 	{  }
 };
@@ -360,9 +359,9 @@ webcam_bind(struct usb_composite_dev *cdev)
 	if (ret < 0)
 		goto error;
 	webcam_device_descriptor.iManufacturer =
-		webcam_strings[STRING_MANUFACTURER_IDX].id;
+		webcam_strings[USB_GADGET_MANUFACTURER_IDX].id;
 	webcam_device_descriptor.iProduct =
-		webcam_strings[STRING_PRODUCT_IDX].id;
+		webcam_strings[USB_GADGET_PRODUCT_IDX].id;
 	webcam_config_driver.iConfiguration =
 		webcam_strings[STRING_DESCRIPTION_IDX].id;
 

drivers/usb/gadget/zero.c

@@ -139,20 +139,15 @@ const struct usb_descriptor_header *otg_desc[] = {
 #endif
 
 /* string IDs are assigned dynamically */
-
-#define STRING_MANUFACTURER_IDX		0
-#define STRING_PRODUCT_IDX		1
-#define STRING_SERIAL_IDX		2
-
 static char manufacturer[50];
 
 /* default serial number takes at least two packets */
 static char serial[] = "0123456789.0123456789.0123456789";
 
 static struct usb_string strings_dev[] = {
-	[STRING_MANUFACTURER_IDX].s = manufacturer,
-	[STRING_PRODUCT_IDX].s = longname,
-	[STRING_SERIAL_IDX].s = serial,
+	[USB_GADGET_MANUFACTURER_IDX].s = manufacturer,
+	[USB_GADGET_PRODUCT_IDX].s = longname,
+	[USB_GADGET_SERIAL_IDX].s = serial,
 	{  }			/* end of list */
 };
 
@@ -274,9 +269,9 @@ static int __init zero_bind(struct usb_composite_dev *cdev)
 	if (status < 0)
 		return status;
 
-	device_desc.iManufacturer = strings_dev[STRING_MANUFACTURER_IDX].id;
-	device_desc.iProduct = strings_dev[STRING_PRODUCT_IDX].id;
-	device_desc.iSerialNumber = strings_dev[STRING_SERIAL_IDX].id;
+	device_desc.iManufacturer = strings_dev[USB_GADGET_MANUFACTURER_IDX].id;
+	device_desc.iProduct = strings_dev[USB_GADGET_PRODUCT_IDX].id;
+	device_desc.iSerialNumber = strings_dev[USB_GADGET_SERIAL_IDX].id;
 
 	setup_timer(&autoresume_timer, zero_autoresume, (unsigned long) cdev);
 

include/linux/usb/composite.h

@@ -248,6 +248,14 @@ int usb_add_config(struct usb_composite_dev *,
 void usb_remove_config(struct usb_composite_dev *,
 		struct usb_configuration *);
 
+/* predefined index for usb_composite_driver */
+enum {
+	USB_GADGET_MANUFACTURER_IDX	= 0,
+	USB_GADGET_PRODUCT_IDX,
+	USB_GADGET_SERIAL_IDX,
+	USB_GADGET_FIRST_AVAIL_IDX,
+};
+
 /**
  * struct usb_composite_driver - groups configurations into a gadget
  * @name: For diagnostics, identifies the driver.
@@ -261,7 +269,9 @@ void usb_remove_config(struct usb_composite_dev *,
  * @dev: Template descriptor for the device, including default device
  *	identifiers.
  * @strings: tables of strings, keyed by identifiers assigned during @bind
- *	and language IDs provided in control requests
+ *	and language IDs provided in control requests. Note: The first entries
+ *	are predefined. The first entry that may be used is
+ *	USB_GADGET_FIRST_AVAIL_IDX
  * @max_speed: Highest speed the driver supports.
  * @needs_serial: set to 1 if the gadget needs userspace to provide
  * 	a serial number.  If one is not provided, warning will be printed.