usb gadget serial: split out CDC ACM function

Split out CDC ACM parts of "gadget serial" to a "function driver".
Some key structural differences from the previous ACM support, shared
with with the generic serial function (next patch):

 - As a function driver, it can be combined with other functions.
   One gadget configuration could offer both serial and network
   links, as an example.

 - One serial port can be exposed in multiple configurations;
   the /dev/ttyGS0 node could be exposed regardless of which
   config the host selected.

 - One configuration can expose multiple serial ports, such as
   ttyGS0, ttyGS1, ttyGS2, and ttyGS3.

This code should be a lot easier to understand than the previous
all-in-one-big-file version of the driver.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

4 files changed, 597 insertions, 6 deletions

diff --git a/Documentation/DocBook/gadget.tmpl b/Documentation/DocBook/gadget.tmpl
index 478bfe16a19d..b7e266c48ac8 100644
--- a/Documentation/DocBook/gadget.tmpl
+++ b/Documentation/DocBook/gadget.tmpl
@@ -556,6 +556,8 @@ been converted to this framework.
 Near-term plans include converting all of them, except for "gadgetfs".
 </para>
 
+!Edrivers/usb/gadget/f_acm.c
+
 </sect1>
 
 
diff --git a/drivers/usb/gadget/Makefile b/drivers/usb/gadget/Makefile
index fe60cca704d9..e438a018ad67 100644
--- a/drivers/usb/gadget/Makefile
+++ b/drivers/usb/gadget/Makefile
@@ -26,7 +26,7 @@ C_UTILS =	composite.o usbstring.o config.o epautoconf.o
 
 g_zero-objs			:= zero.o f_sourcesink.o f_loopback.o $(C_UTILS)
 g_ether-objs			:= ether.o usbstring.o config.o epautoconf.o
-g_serial-objs			:= serial.o u_serial.o usbstring.o config.o epautoconf.o
+g_serial-objs			:= serial.o u_serial.o f_acm.o $(C_UTILS)
 g_midi-objs			:= gmidi.o usbstring.o config.o epautoconf.o
 gadgetfs-objs			:= inode.o
 g_file_storage-objs		:= file_storage.o usbstring.o config.o \
diff --git a/drivers/usb/gadget/f_acm.c b/drivers/usb/gadget/f_acm.c
new file mode 100644
index 000000000000..d8faccf27895
--- /dev/null
+++ b/drivers/usb/gadget/f_acm.c
@@ -0,0 +1,589 @@
+/*
+ * f_acm.c -- USB CDC serial (ACM) function driver
+ *
+ * Copyright (C) 2003 Al Borchers (alborchers@steinerpoint.com)
+ * Copyright (C) 2008 by David Brownell
+ * Copyright (C) 2008 by Nokia Corporation
+ *
+ * This software is distributed under the terms of the GNU General
+ * Public License ("GPL") as published by the Free Software Foundation,
+ * either version 2 of that License or (at your option) any later version.
+ */
+
+/* #define VERBOSE_DEBUG */
+
+#include <linux/kernel.h>
+#include <linux/device.h>
+
+#include "u_serial.h"
+#include "gadget_chips.h"
+
+
+/*
+ * This CDC ACM function support just wraps control functions and
+ * notifications around the generic serial-over-usb code.
+ *
+ * Because CDC ACM is standardized by the USB-IF, many host operating
+ * systems have drivers for it.  Accordingly, ACM is the preferred
+ * interop solution for serial-port type connections.  The control
+ * models are often not necessary, and in any case don't do much in
+ * this bare-bones implementation.
+ *
+ * Note that even MS-Windows has some support for ACM.  However, that
+ * support is somewhat broken because when you use ACM in a composite
+ * device, having multiple interfaces confuses the poor OS.  It doesn't
+ * seem to understand CDC Union descriptors.  The new "association"
+ * descriptors (roughly equivalent to CDC Unions) may sometimes help.
+ */
+
+struct acm_ep_descs {
+	struct usb_endpoint_descriptor	*in;
+	struct usb_endpoint_descriptor	*out;
+	struct usb_endpoint_descriptor	*notify;
+};
+
+struct f_acm {
+	struct gserial			port;
+	u8				ctrl_id, data_id;
+	u8				port_num;
+
+	struct usb_descriptor_header	**fs_function;
+	struct acm_ep_descs		fs;
+	struct usb_descriptor_header	**hs_function;
+	struct acm_ep_descs		hs;
+
+	struct usb_ep			*notify;
+	struct usb_endpoint_descriptor	*notify_desc;
+
+	struct usb_cdc_line_coding	port_line_coding;	/* 8-N-1 etc */
+	u16				port_handshake_bits;
+#define RS232_RTS	(1 << 1)	/* unused with full duplex */
+#define RS232_DTR	(1 << 0)	/* host is ready for data r/w */
+};
+
+static inline struct f_acm *func_to_acm(struct usb_function *f)
+{
+	return container_of(f, struct f_acm, port.func);
+}
+
+/*-------------------------------------------------------------------------*/
+
+/* notification endpoint uses smallish and infrequent fixed-size messages */
+
+#define GS_LOG2_NOTIFY_INTERVAL		5	/* 1 << 5 == 32 msec */
+#define GS_NOTIFY_MAXPACKET		8
+
+/* interface and class descriptors: */
+
+static struct usb_interface_descriptor acm_control_interface_desc __initdata = {
+	.bLength =		USB_DT_INTERFACE_SIZE,
+	.bDescriptorType =	USB_DT_INTERFACE,
+	/* .bInterfaceNumber = DYNAMIC */
+	.bNumEndpoints =	1,
+	.bInterfaceClass =	USB_CLASS_COMM,
+	.bInterfaceSubClass =	USB_CDC_SUBCLASS_ACM,
+	.bInterfaceProtocol =	USB_CDC_ACM_PROTO_AT_V25TER,
+	/* .iInterface = DYNAMIC */
+};
+
+static struct usb_interface_descriptor acm_data_interface_desc __initdata = {
+	.bLength =		USB_DT_INTERFACE_SIZE,
+	.bDescriptorType =	USB_DT_INTERFACE,
+	/* .bInterfaceNumber = DYNAMIC */
+	.bNumEndpoints =	2,
+	.bInterfaceClass =	USB_CLASS_CDC_DATA,
+	.bInterfaceSubClass =	0,
+	.bInterfaceProtocol =	0,
+	/* .iInterface = DYNAMIC */
+};
+
+static struct usb_cdc_header_desc acm_header_desc __initdata = {
+	.bLength =		sizeof(acm_header_desc),
+	.bDescriptorType =	USB_DT_CS_INTERFACE,
+	.bDescriptorSubType =	USB_CDC_HEADER_TYPE,
+	.bcdCDC =		__constant_cpu_to_le16(0x0110),
+};
+
+static struct usb_cdc_call_mgmt_descriptor
+acm_call_mgmt_descriptor __initdata = {
+	.bLength =		sizeof(acm_call_mgmt_descriptor),
+	.bDescriptorType =	USB_DT_CS_INTERFACE,
+	.bDescriptorSubType =	USB_CDC_CALL_MANAGEMENT_TYPE,
+	.bmCapabilities =	0,
+	/* .bDataInterface = DYNAMIC */
+};
+
+static struct usb_cdc_acm_descriptor acm_descriptor __initdata = {
+	.bLength =		sizeof(acm_descriptor),
+	.bDescriptorType =	USB_DT_CS_INTERFACE,
+	.bDescriptorSubType =	USB_CDC_ACM_TYPE,
+	.bmCapabilities =	(1 << 1),
+};
+
+static struct usb_cdc_union_desc acm_union_desc __initdata = {
+	.bLength =		sizeof(acm_union_desc),
+	.bDescriptorType =	USB_DT_CS_INTERFACE,
+	.bDescriptorSubType =	USB_CDC_UNION_TYPE,
+	/* .bMasterInterface0 =	DYNAMIC */
+	/* .bSlaveInterface0 =	DYNAMIC */
+};
+
+/* full speed support: */
+
+static struct usb_endpoint_descriptor acm_fs_notify_desc __initdata = {
+	.bLength =		USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType =	USB_DT_ENDPOINT,
+	.bEndpointAddress =	USB_DIR_IN,
+	.bmAttributes =		USB_ENDPOINT_XFER_INT,
+	.wMaxPacketSize =	__constant_cpu_to_le16(GS_NOTIFY_MAXPACKET),
+	.bInterval =		1 << GS_LOG2_NOTIFY_INTERVAL,
+};
+
+static struct usb_endpoint_descriptor acm_fs_in_desc __initdata = {
+	.bLength =		USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType =	USB_DT_ENDPOINT,
+	.bEndpointAddress =	USB_DIR_IN,
+	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
+};
+
+static struct usb_endpoint_descriptor acm_fs_out_desc __initdata = {
+	.bLength =		USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType =	USB_DT_ENDPOINT,
+	.bEndpointAddress =	USB_DIR_OUT,
+	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
+};
+
+static struct usb_descriptor_header *acm_fs_function[] __initdata = {
+	(struct usb_descriptor_header *) &acm_control_interface_desc,
+	(struct usb_descriptor_header *) &acm_header_desc,
+	(struct usb_descriptor_header *) &acm_call_mgmt_descriptor,
+	(struct usb_descriptor_header *) &acm_descriptor,
+	(struct usb_descriptor_header *) &acm_union_desc,
+	(struct usb_descriptor_header *) &acm_fs_notify_desc,
+	(struct usb_descriptor_header *) &acm_data_interface_desc,
+	(struct usb_descriptor_header *) &acm_fs_in_desc,
+	(struct usb_descriptor_header *) &acm_fs_out_desc,
+	NULL,
+};
+
+/* high speed support: */
+
+static struct usb_endpoint_descriptor acm_hs_notify_desc __initdata = {
+	.bLength =		USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType =	USB_DT_ENDPOINT,
+	.bEndpointAddress =	USB_DIR_IN,
+	.bmAttributes =		USB_ENDPOINT_XFER_INT,
+	.wMaxPacketSize =	__constant_cpu_to_le16(GS_NOTIFY_MAXPACKET),
+	.bInterval =		GS_LOG2_NOTIFY_INTERVAL+4,
+};
+
+static struct usb_endpoint_descriptor acm_hs_in_desc __initdata = {
+	.bLength =		USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType =	USB_DT_ENDPOINT,
+	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
+	.wMaxPacketSize =	__constant_cpu_to_le16(512),
+};
+
+static struct usb_endpoint_descriptor acm_hs_out_desc __initdata = {
+	.bLength =		USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType =	USB_DT_ENDPOINT,
+	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
+	.wMaxPacketSize =	__constant_cpu_to_le16(512),
+};
+
+static struct usb_descriptor_header *acm_hs_function[] __initdata = {
+	(struct usb_descriptor_header *) &acm_control_interface_desc,
+	(struct usb_descriptor_header *) &acm_header_desc,
+	(struct usb_descriptor_header *) &acm_call_mgmt_descriptor,
+	(struct usb_descriptor_header *) &acm_descriptor,
+	(struct usb_descriptor_header *) &acm_union_desc,
+	(struct usb_descriptor_header *) &acm_hs_notify_desc,
+	(struct usb_descriptor_header *) &acm_data_interface_desc,
+	(struct usb_descriptor_header *) &acm_hs_in_desc,
+	(struct usb_descriptor_header *) &acm_hs_out_desc,
+	NULL,
+};
+
+/* string descriptors: */
+
+#define ACM_CTRL_IDX	0
+#define ACM_DATA_IDX	1
+
+/* static strings, in UTF-8 */
+static struct usb_string acm_string_defs[] = {
+	[ACM_CTRL_IDX].s = "CDC Abstract Control Model (ACM)",
+	[ACM_DATA_IDX].s = "CDC ACM Data",
+	{  /* ZEROES END LIST */ },
+};
+
+static struct usb_gadget_strings acm_string_table = {
+	.language =		0x0409,	/* en-us */
+	.strings =		acm_string_defs,
+};
+
+static struct usb_gadget_strings *acm_strings[] = {
+	&acm_string_table,
+	NULL,
+};
+
+/*-------------------------------------------------------------------------*/
+
+/* ACM control ... data handling is delegated to tty library code.
+ * The main task of this function is to activate and deactivate
+ * that code based on device state; track parameters like line
+ * speed, handshake state, and so on; and issue notifications.
+ */
+
+static void acm_complete_set_line_coding(struct usb_ep *ep,
+		struct usb_request *req)
+{
+	struct f_acm	*acm = ep->driver_data;
+	struct usb_composite_dev *cdev = acm->port.func.config->cdev;
+
+	if (req->status != 0) {
+		DBG(cdev, "acm ttyGS%d completion, err %d\n",
+				acm->port_num, req->status);
+		return;
+	}
+
+	/* normal completion */
+	if (req->actual != sizeof(acm->port_line_coding)) {
+		DBG(cdev, "acm ttyGS%d short resp, len %d\n",
+				acm->port_num, req->actual);
+		usb_ep_set_halt(ep);
+	} else {
+		struct usb_cdc_line_coding	*value = req->buf;
+
+		/* REVISIT:  we currently just remember this data.
+		 * If we change that, (a) validate it first, then
+		 * (b) update whatever hardware needs updating,
+		 * (c) worry about locking.  This is information on
+		 * the order of 9600-8-N-1 ... most of which means
+		 * nothing unless we control a real RS232 line.
+		 */
+		acm->port_line_coding = *value;
+	}
+}
+
+static int acm_setup(struct usb_function *f, const struct usb_ctrlrequest *ctrl)
+{
+	struct f_acm		*acm = func_to_acm(f);
+	struct usb_composite_dev *cdev = f->config->cdev;
+	struct usb_request	*req = cdev->req;
+	int			value = -EOPNOTSUPP;
+	u16			w_index = le16_to_cpu(ctrl->wIndex);
+	u16			w_value = le16_to_cpu(ctrl->wValue);
+	u16			w_length = le16_to_cpu(ctrl->wLength);
+
+	/* composite driver infrastructure handles everything except
+	 * CDC class messages; interface activation uses set_alt().
+	 */
+	switch ((ctrl->bRequestType << 8) | ctrl->bRequest) {
+
+	/* SET_LINE_CODING ... just read and save what the host sends */
+	case ((USB_DIR_OUT | USB_TYPE_CLASS | USB_RECIP_INTERFACE) << 8)
+			| USB_CDC_REQ_SET_LINE_CODING:
+		if (w_length != sizeof(struct usb_cdc_line_coding)
+				|| w_index != acm->ctrl_id)
+			goto invalid;
+
+		value = w_length;
+		cdev->gadget->ep0->driver_data = acm;
+		req->complete = acm_complete_set_line_coding;
+		break;
+
+	/* GET_LINE_CODING ... return what host sent, or initial value */
+	case ((USB_DIR_IN | USB_TYPE_CLASS | USB_RECIP_INTERFACE) << 8)
+			| USB_CDC_REQ_GET_LINE_CODING:
+		if (w_index != acm->ctrl_id)
+			goto invalid;
+
+		value = min_t(unsigned, w_length,
+				sizeof(struct usb_cdc_line_coding));
+		memcpy(req->buf, &acm->port_line_coding, value);
+		break;
+
+	/* SET_CONTROL_LINE_STATE ... save what the host sent */
+	case ((USB_DIR_OUT | USB_TYPE_CLASS | USB_RECIP_INTERFACE) << 8)
+			| USB_CDC_REQ_SET_CONTROL_LINE_STATE:
+		if (w_index != acm->ctrl_id)
+			goto invalid;
+
+		value = 0;
+
+		/* FIXME we should not allow data to flow until the
+		 * host sets the RS232_DTR bit; and when it clears
+		 * that bit, we should return to that no-flow state.
+		 */
+		acm->port_handshake_bits = w_value;
+		break;
+
+	default:
+invalid:
+		VDBG(cdev, "invalid control req%02x.%02x v%04x i%04x l%d\n",
+			ctrl->bRequestType, ctrl->bRequest,
+			w_value, w_index, w_length);
+	}
+
+	/* respond with data transfer or status phase? */
+	if (value >= 0) {
+		DBG(cdev, "acm ttyGS%d req%02x.%02x v%04x i%04x l%d\n",
+			acm->port_num, ctrl->bRequestType, ctrl->bRequest,
+			w_value, w_index, w_length);
+		req->zero = 0;
+		req->length = value;
+		value = usb_ep_queue(cdev->gadget->ep0, req, GFP_ATOMIC);
+		if (value < 0)
+			ERROR(cdev, "acm response on ttyGS%d, err %d\n",
+					acm->port_num, value);
+	}
+
+	/* device either stalls (value < 0) or reports success */
+	return value;
+}
+
+static int acm_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
+{
+	struct f_acm		*acm = func_to_acm(f);
+	struct usb_composite_dev *cdev = f->config->cdev;
+
+	/* we know alt == 0, so this is an activation or a reset */
+
+	if (intf == acm->ctrl_id) {
+		/* REVISIT this may need more work when we start to
+		 * send notifications ...
+		 */
+		if (acm->notify->driver_data) {
+			VDBG(cdev, "reset acm control interface %d\n", intf);
+			usb_ep_disable(acm->notify);
+		} else {
+			VDBG(cdev, "init acm ctrl interface %d\n", intf);
+			acm->notify_desc = ep_choose(cdev->gadget,
+					acm->hs.notify,
+					acm->fs.notify);
+		}
+		usb_ep_enable(acm->notify, acm->notify_desc);
+		acm->notify->driver_data = acm;
+
+	} else if (intf == acm->data_id) {
+		if (acm->port.in->driver_data) {
+			DBG(cdev, "reset acm ttyGS%d\n", acm->port_num);
+			gserial_disconnect(&acm->port);
+		} else {
+			DBG(cdev, "activate acm ttyGS%d\n", acm->port_num);
+			acm->port.in_desc = ep_choose(cdev->gadget,
+					acm->hs.in, acm->fs.in);
+			acm->port.out_desc = ep_choose(cdev->gadget,
+					acm->hs.out, acm->fs.out);
+		}
+		gserial_connect(&acm->port, acm->port_num);
+
+	} else
+		return -EINVAL;
+
+	return 0;
+}
+
+static void acm_disable(struct usb_function *f)
+{
+	struct f_acm	*acm = func_to_acm(f);
+	struct usb_composite_dev *cdev = f->config->cdev;
+
+	DBG(cdev, "acm ttyGS%d deactivated\n", acm->port_num);
+	gserial_disconnect(&acm->port);
+	usb_ep_disable(acm->notify);
+	acm->notify->driver_data = NULL;
+}
+
+/*-------------------------------------------------------------------------*/
+
+/* ACM function driver setup/binding */
+static int __init
+acm_bind(struct usb_configuration *c, struct usb_function *f)
+{
+	struct usb_composite_dev *cdev = c->cdev;
+	struct f_acm		*acm = func_to_acm(f);
+	int			status;
+	struct usb_ep		*ep;
+
+	/* allocate instance-specific interface IDs, and patch descriptors */
+	status = usb_interface_id(c, f);
+	if (status < 0)
+		goto fail;
+	acm->ctrl_id = status;
+
+	acm_control_interface_desc.bInterfaceNumber = status;
+	acm_union_desc .bMasterInterface0 = status;
+
+	status = usb_interface_id(c, f);
+	if (status < 0)
+		goto fail;
+	acm->data_id = status;
+
+	acm_data_interface_desc.bInterfaceNumber = status;
+	acm_union_desc.bSlaveInterface0 = status;
+	acm_call_mgmt_descriptor.bDataInterface = status;
+
+	status = -ENODEV;
+
+	/* allocate instance-specific endpoints */
+	ep = usb_ep_autoconfig(cdev->gadget, &acm_fs_in_desc);
+	if (!ep)
+		goto fail;
+	acm->port.in = ep;
+	ep->driver_data = cdev;	/* claim */
+
+	ep = usb_ep_autoconfig(cdev->gadget, &acm_fs_out_desc);
+	if (!ep)
+		goto fail;
+	acm->port.out = ep;
+	ep->driver_data = cdev;	/* claim */
+
+	ep = usb_ep_autoconfig(cdev->gadget, &acm_fs_notify_desc);
+	if (!ep)
+		goto fail;
+	acm->notify = ep;
+	ep->driver_data = cdev;	/* claim */
+
+	/* copy descriptors, and track endpoint copies */
+	f->descriptors = usb_copy_descriptors(acm_fs_function);
+
+	acm->fs.in = usb_find_endpoint(acm_fs_function,
+			f->descriptors, &acm_fs_in_desc);
+	acm->fs.out = usb_find_endpoint(acm_fs_function,
+			f->descriptors, &acm_fs_out_desc);
+	acm->fs.notify = usb_find_endpoint(acm_fs_function,
+			f->descriptors, &acm_fs_notify_desc);
+
+	/* support all relevant hardware speeds... we expect that when
+	 * hardware is dual speed, all bulk-capable endpoints work at
+	 * both speeds
+	 */
+	if (gadget_is_dualspeed(c->cdev->gadget)) {
+		acm_hs_in_desc.bEndpointAddress =
+				acm_fs_in_desc.bEndpointAddress;
+		acm_hs_out_desc.bEndpointAddress =
+				acm_fs_out_desc.bEndpointAddress;
+		acm_hs_notify_desc.bEndpointAddress =
+				acm_fs_notify_desc.bEndpointAddress;
+
+		/* copy descriptors, and track endpoint copies */
+		f->hs_descriptors = usb_copy_descriptors(acm_hs_function);
+
+		acm->hs.in = usb_find_endpoint(acm_hs_function,
+				f->hs_descriptors, &acm_hs_in_desc);
+		acm->hs.out = usb_find_endpoint(acm_hs_function,
+				f->hs_descriptors, &acm_hs_out_desc);
+		acm->hs.notify = usb_find_endpoint(acm_hs_function,
+				f->hs_descriptors, &acm_hs_notify_desc);
+	}
+
+	/* FIXME provide a callback for triggering notifications */
+
+	DBG(cdev, "acm ttyGS%d: %s speed IN/%s OUT/%s NOTIFY/%s\n",
+			acm->port_num,
+			gadget_is_dualspeed(c->cdev->gadget) ? "dual" : "full",
+			acm->port.in->name, acm->port.out->name,
+			acm->notify->name);
+	return 0;
+
+fail:
+	/* we might as well release our claims on endpoints */
+	if (acm->notify)
+		acm->notify->driver_data = NULL;
+	if (acm->port.out)
+		acm->port.out->driver_data = NULL;
+	if (acm->port.in)
+		acm->port.in->driver_data = NULL;
+
+	ERROR(cdev, "%s/%p: can't bind, err %d\n", f->name, f, status);
+
+	return status;
+}
+
+static void
+acm_unbind(struct usb_configuration *c, struct usb_function *f)
+{
+	if (gadget_is_dualspeed(c->cdev->gadget))
+		usb_free_descriptors(f->hs_descriptors);
+	usb_free_descriptors(f->descriptors);
+	kfree(func_to_acm(f));
+}
+
+/* Some controllers can't support CDC ACM ... */
+static inline bool can_support_cdc(struct usb_configuration *c)
+{
+	/* SH3 doesn't support multiple interfaces */
+	if (gadget_is_sh(c->cdev->gadget))
+		return false;
+
+	/* sa1100 doesn't have a third interrupt endpoint */
+	if (gadget_is_sa1100(c->cdev->gadget))
+		return false;
+
+	/* everything else is *probably* fine ... */
+	return true;
+}
+
+/**
+ * acm_bind_config - add a CDC ACM function to a configuration
+ * @c: the configuration to support the CDC ACM instance
+ * @port_num: /dev/ttyGS* port this interface will use
+ * Context: single threaded during gadget setup
+ *
+ * Returns zero on success, else negative errno.
+ *
+ * Caller must have called @gserial_setup() with enough ports to
+ * handle all the ones it binds.  Caller is also responsible
+ * for calling @gserial_cleanup() before module unload.
+ */
+int __init acm_bind_config(struct usb_configuration *c, u8 port_num)
+{
+	struct f_acm	*acm;
+	int		status;
+
+	if (!can_support_cdc(c))
+		return -EINVAL;
+
+	/* REVISIT might want instance-specific strings to help
+	 * distinguish instances ...
+	 */
+
+	/* maybe allocate device-global string IDs, and patch descriptors */
+	if (acm_string_defs[ACM_CTRL_IDX].id == 0) {
+		status = usb_string_id(c->cdev);
+		if (status < 0)
+			return status;
+		acm_string_defs[ACM_CTRL_IDX].id = status;
+
+		acm_control_interface_desc.iInterface = status;
+
+		status = usb_string_id(c->cdev);
+		if (status < 0)
+			return status;
+		acm_string_defs[ACM_DATA_IDX].id = status;
+
+		acm_data_interface_desc.iInterface = status;
+	}
+
+	/* allocate and initialize one new instance */
+	acm = kzalloc(sizeof *acm, GFP_KERNEL);
+	if (!acm)
+		return -ENOMEM;
+
+	acm->port_num = port_num;
+
+	acm->port.func.name = "acm";
+	acm->port.func.strings = acm_strings;
+	/* descriptors are per-instance copies */
+	acm->port.func.bind = acm_bind;
+	acm->port.func.unbind = acm_unbind;
+	acm->port.func.set_alt = acm_set_alt;
+	acm->port.func.setup = acm_setup;
+	acm->port.func.disable = acm_disable;
+
+	status = usb_add_function(c, &acm->port.func);
+	if (status)
+		kfree(acm);
+	return status;
+}
diff --git a/drivers/usb/gadget/u_serial.h b/drivers/usb/gadget/u_serial.h
index bc38e68d0f26..83b45a3801ff 100644
--- a/drivers/usb/gadget/u_serial.h
+++ b/drivers/usb/gadget/u_serial.h
@@ -12,10 +12,7 @@
 #ifndef __U_SERIAL_H
 #define __U_SERIAL_H
 
-/* #include <linux/usb/composite.h> */
-#include <linux/usb/ch9.h>
-#include <linux/usb/gadget.h>
-
+#include <linux/usb/composite.h>
 #include <linux/usb/cdc.h>
 
 /*
@@ -32,7 +29,7 @@
  * REVISIT someday, allow multiplexing several TTYs over these endpoints.
  */
 struct gserial {
-	/* struct usb_function		func; */
+	struct usb_function		func;
 
 	/* port is managed by gserial_{connect,disconnect} */
 	struct gs_port			*ioport;
@@ -59,4 +56,7 @@ void gserial_cleanup(void);
 int gserial_connect(struct gserial *, u8 port_num);
 void gserial_disconnect(struct gserial *);
 
+/* functions are bound to configurations by a config or gadget driver */
+int acm_bind_config(struct usb_configuration *c, u8 port_num);
+
 #endif /* __U_SERIAL_H */