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 */