drivers/usb/gadget/f_subset.c - arm/linux-arm-legacy - Git at Google

 /*
  * f_subset.c -- "CDC Subset" Ethernet link function driver
  *
  * Copyright (C) 2003-2005,2008 David Brownell
  * Copyright (C) 2008 Nokia Corporation
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or
  * (at your option) any later version.
  */

 #include <linux/slab.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/device.h>
 #include <linux/etherdevice.h>

 #include "u_ether.h"
 #include "u_ether_configfs.h"
 #include "u_gether.h"

 /*
  * This function packages a simple "CDC Subset" Ethernet port with no real
  * control mechanisms; just raw data transfer over two bulk endpoints.
  * The data transfer model is exactly that of CDC Ethernet, which is
  * why we call it the "CDC Subset".
  *
  * Because it's not standardized, this has some interoperability issues.
  * They mostly relate to driver binding, since the data transfer model is
  * so simple (CDC Ethernet).  The original versions of this protocol used
  * specific product/vendor IDs:  byteswapped IDs for Digital Equipment's
  * SA-1100 "Itsy" board, which could run Linux 2.4 kernels and supported
  * daughtercards with USB peripheral connectors.  (It was used more often
  * with other boards, using the Itsy identifiers.)  Linux hosts recognized
  * this with CONFIG_USB_ARMLINUX; these devices have only one configuration
  * and one interface.
  *
  * At some point, MCCI defined a (nonconformant) CDC MDLM variant called
  * "SAFE", which happens to have a mode which is identical to the "CDC
  * Subset" in terms of data transfer and lack of control model.  This was
  * adopted by later Sharp Zaurus models, and by some other software which
  * Linux hosts recognize with CONFIG_USB_NET_ZAURUS.
  *
  * Because Microsoft's RNDIS drivers are far from robust, we added a few
  * descriptors to the CDC Subset code, making this code look like a SAFE
  * implementation.  This lets you use MCCI's host side MS-Windows drivers
  * if you get fed up with RNDIS.  It also makes it easier for composite
  * drivers to work, since they can use class based binding instead of
  * caring about specific product and vendor IDs.
  */

 struct f_gether {
 	struct gether			port;

 	char				ethaddr[14];
 };

 static inline struct f_gether *func_to_geth(struct usb_function *f)
 {
 	return container_of(f, struct f_gether, port.func);
 }

 /*-------------------------------------------------------------------------*/

 /*
  * "Simple" CDC-subset option is a simple vendor-neutral model that most
  * full speed controllers can handle:  one interface, two bulk endpoints.
  * To assist host side drivers, we fancy it up a bit, and add descriptors so
  * some host side drivers will understand it as a "SAFE" variant.
  *
  * "SAFE" loosely follows CDC WMC MDLM, violating the spec in various ways.
  * Data endpoints live in the control interface, there's no data interface.
  * And it's not used to talk to a cell phone radio.
  */

 /* interface descriptor: */

 static struct usb_interface_descriptor subset_data_intf = {
 	.bLength =		sizeof subset_data_intf,
 	.bDescriptorType =	USB_DT_INTERFACE,

 	/* .bInterfaceNumber = DYNAMIC */
 	.bAlternateSetting =	0,
 	.bNumEndpoints =	2,
 	.bInterfaceClass =      USB_CLASS_COMM,
 	.bInterfaceSubClass =	USB_CDC_SUBCLASS_MDLM,
 	.bInterfaceProtocol =	0,
 	/* .iInterface = DYNAMIC */
 };

 static struct usb_cdc_header_desc mdlm_header_desc = {
 	.bLength =		sizeof mdlm_header_desc,
 	.bDescriptorType =	USB_DT_CS_INTERFACE,
 	.bDescriptorSubType =	USB_CDC_HEADER_TYPE,

 	.bcdCDC =		cpu_to_le16(0x0110),
 };

 static struct usb_cdc_mdlm_desc mdlm_desc = {
 	.bLength =		sizeof mdlm_desc,
 	.bDescriptorType =	USB_DT_CS_INTERFACE,
 	.bDescriptorSubType =	USB_CDC_MDLM_TYPE,

 	.bcdVersion =		cpu_to_le16(0x0100),
 	.bGUID = {
 		0x5d, 0x34, 0xcf, 0x66, 0x11, 0x18, 0x11, 0xd6,
 		0xa2, 0x1a, 0x00, 0x01, 0x02, 0xca, 0x9a, 0x7f,
 	},
 };

 /* since "usb_cdc_mdlm_detail_desc" is a variable length structure, we
  * can't really use its struct.  All we do here is say that we're using
  * the submode of "SAFE" which directly matches the CDC Subset.
  */
 static u8 mdlm_detail_desc[] = {
 	6,
 	USB_DT_CS_INTERFACE,
 	USB_CDC_MDLM_DETAIL_TYPE,

 	0,	/* "SAFE" */
 	0,	/* network control capabilities (none) */
 	0,	/* network data capabilities ("raw" encapsulation) */
 };

 static struct usb_cdc_ether_desc ether_desc = {
 	.bLength =		sizeof ether_desc,
 	.bDescriptorType =	USB_DT_CS_INTERFACE,
 	.bDescriptorSubType =	USB_CDC_ETHERNET_TYPE,

 	/* this descriptor actually adds value, surprise! */
 	/* .iMACAddress = DYNAMIC */
 	.bmEthernetStatistics =	cpu_to_le32(0), /* no statistics */
 	.wMaxSegmentSize =	cpu_to_le16(ETH_FRAME_LEN),
 	.wNumberMCFilters =	cpu_to_le16(0),
 	.bNumberPowerFilters =	0,
 };

 /* full speed support: */

 static struct usb_endpoint_descriptor fs_subset_in_desc = {
 	.bLength =		USB_DT_ENDPOINT_SIZE,
 	.bDescriptorType =	USB_DT_ENDPOINT,

 	.bEndpointAddress =	USB_DIR_IN,
 	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
 };

 static struct usb_endpoint_descriptor fs_subset_out_desc = {
 	.bLength =		USB_DT_ENDPOINT_SIZE,
 	.bDescriptorType =	USB_DT_ENDPOINT,

 	.bEndpointAddress =	USB_DIR_OUT,
 	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
 };

 static struct usb_descriptor_header *fs_eth_function[] = {
 	(struct usb_descriptor_header *) &subset_data_intf,
 	(struct usb_descriptor_header *) &mdlm_header_desc,
 	(struct usb_descriptor_header *) &mdlm_desc,
 	(struct usb_descriptor_header *) &mdlm_detail_desc,
 	(struct usb_descriptor_header *) &ether_desc,
 	(struct usb_descriptor_header *) &fs_subset_in_desc,
 	(struct usb_descriptor_header *) &fs_subset_out_desc,
 	NULL,
 };

 /* high speed support: */

 static struct usb_endpoint_descriptor hs_subset_in_desc = {
 	.bLength =		USB_DT_ENDPOINT_SIZE,
 	.bDescriptorType =	USB_DT_ENDPOINT,

 	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
 	.wMaxPacketSize =	cpu_to_le16(512),
 };

 static struct usb_endpoint_descriptor hs_subset_out_desc = {
 	.bLength =		USB_DT_ENDPOINT_SIZE,
 	.bDescriptorType =	USB_DT_ENDPOINT,

 	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
 	.wMaxPacketSize =	cpu_to_le16(512),
 };

 static struct usb_descriptor_header *hs_eth_function[] = {
 	(struct usb_descriptor_header *) &subset_data_intf,
 	(struct usb_descriptor_header *) &mdlm_header_desc,
 	(struct usb_descriptor_header *) &mdlm_desc,
 	(struct usb_descriptor_header *) &mdlm_detail_desc,
 	(struct usb_descriptor_header *) &ether_desc,
 	(struct usb_descriptor_header *) &hs_subset_in_desc,
 	(struct usb_descriptor_header *) &hs_subset_out_desc,
 	NULL,
 };

 /* super speed support: */

 static struct usb_endpoint_descriptor ss_subset_in_desc = {
 	.bLength =		USB_DT_ENDPOINT_SIZE,
 	.bDescriptorType =	USB_DT_ENDPOINT,

 	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
 	.wMaxPacketSize =	cpu_to_le16(1024),
 };

 static struct usb_endpoint_descriptor ss_subset_out_desc = {
 	.bLength =		USB_DT_ENDPOINT_SIZE,
 	.bDescriptorType =	USB_DT_ENDPOINT,

 	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
 	.wMaxPacketSize =	cpu_to_le16(1024),
 };

 static struct usb_ss_ep_comp_descriptor ss_subset_bulk_comp_desc = {
 	.bLength =		sizeof ss_subset_bulk_comp_desc,
 	.bDescriptorType =	USB_DT_SS_ENDPOINT_COMP,

 	/* the following 2 values can be tweaked if necessary */
 	/* .bMaxBurst =		0, */
 	/* .bmAttributes =	0, */
 };

 static struct usb_descriptor_header *ss_eth_function[] = {
 	(struct usb_descriptor_header *) &subset_data_intf,
 	(struct usb_descriptor_header *) &mdlm_header_desc,
 	(struct usb_descriptor_header *) &mdlm_desc,
 	(struct usb_descriptor_header *) &mdlm_detail_desc,
 	(struct usb_descriptor_header *) &ether_desc,
 	(struct usb_descriptor_header *) &ss_subset_in_desc,
 	(struct usb_descriptor_header *) &ss_subset_bulk_comp_desc,
 	(struct usb_descriptor_header *) &ss_subset_out_desc,
 	(struct usb_descriptor_header *) &ss_subset_bulk_comp_desc,
 	NULL,
 };

 /* string descriptors: */

 static struct usb_string geth_string_defs[] = {
 	[0].s = "CDC Ethernet Subset/SAFE",
 	[1].s = "",
 	{  } /* end of list */
 };

 static struct usb_gadget_strings geth_string_table = {
 	.language =		0x0409,	/* en-us */
 	.strings =		geth_string_defs,
 };

 static struct usb_gadget_strings *geth_strings[] = {
 	&geth_string_table,
 	NULL,
 };

 /*-------------------------------------------------------------------------*/

 static int geth_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
 {
 	struct f_gether		*geth = func_to_geth(f);
 	struct usb_composite_dev *cdev = f->config->cdev;
 	struct net_device	*net;

 	/* we know alt == 0, so this is an activation or a reset */

 	if (geth->port.in_ep->driver_data) {
 		DBG(cdev, "reset cdc subset\n");
 		gether_disconnect(&geth->port);
 	}

 	DBG(cdev, "init + activate cdc subset\n");
 	if (config_ep_by_speed(cdev->gadget, f, geth->port.in_ep) ||
 	    config_ep_by_speed(cdev->gadget, f, geth->port.out_ep)) {
 		geth->port.in_ep->desc = NULL;
 		geth->port.out_ep->desc = NULL;
 		return -EINVAL;
 	}

 	net = gether_connect(&geth->port);
 	return IS_ERR(net) ? PTR_ERR(net) : 0;
 }

 static void geth_disable(struct usb_function *f)
 {
 	struct f_gether	*geth = func_to_geth(f);
 	struct usb_composite_dev *cdev = f->config->cdev;

 	DBG(cdev, "net deactivated\n");
 	gether_disconnect(&geth->port);
 }

 /*-------------------------------------------------------------------------*/

 /* serial function driver setup/binding */

 static int
 geth_bind(struct usb_configuration *c, struct usb_function *f)
 {
 	struct usb_composite_dev *cdev = c->cdev;
 	struct f_gether		*geth = func_to_geth(f);
 	struct usb_string	*us;
 	int			status;
 	struct usb_ep		*ep;

 	struct f_gether_opts	*gether_opts;

 	gether_opts = container_of(f->fi, struct f_gether_opts, func_inst);

 	/*
 	 * in drivers/usb/gadget/configfs.c:configfs_composite_bind()
 	 * configurations are bound in sequence with list_for_each_entry,
 	 * in each configuration its functions are bound in sequence
 	 * with list_for_each_entry, so we assume no race condition
 	 * with regard to gether_opts->bound access
 	 */
 	if (!gether_opts->bound) {
 		mutex_lock(&gether_opts->lock);
 		gether_set_gadget(gether_opts->net, cdev->gadget);
 		status = gether_register_netdev(gether_opts->net);
 		mutex_unlock(&gether_opts->lock);
 		if (status)
 			return status;
 		gether_opts->bound = true;
 	}

 	us = usb_gstrings_attach(cdev, geth_strings,
 				 ARRAY_SIZE(geth_string_defs));
 	if (IS_ERR(us))
 		return PTR_ERR(us);

 	subset_data_intf.iInterface = us[0].id;
 	ether_desc.iMACAddress = us[1].id;

 	/* allocate instance-specific interface IDs */
 	status = usb_interface_id(c, f);
 	if (status < 0)
 		goto fail;
 	subset_data_intf.bInterfaceNumber = status;

 	status = -ENODEV;

 	/* allocate instance-specific endpoints */
 	ep = usb_ep_autoconfig(cdev->gadget, &fs_subset_in_desc);
 	if (!ep)
 		goto fail;
 	geth->port.in_ep = ep;
 	ep->driver_data = cdev;	/* claim */

 	ep = usb_ep_autoconfig(cdev->gadget, &fs_subset_out_desc);
 	if (!ep)
 		goto fail;
 	geth->port.out_ep = ep;
 	ep->driver_data = cdev;	/* claim */

 	/* support all relevant hardware speeds... we expect that when
 	 * hardware is dual speed, all bulk-capable endpoints work at
 	 * both speeds
 	 */
 	hs_subset_in_desc.bEndpointAddress = fs_subset_in_desc.bEndpointAddress;
 	hs_subset_out_desc.bEndpointAddress =
 		fs_subset_out_desc.bEndpointAddress;

 	ss_subset_in_desc.bEndpointAddress = fs_subset_in_desc.bEndpointAddress;
 	ss_subset_out_desc.bEndpointAddress =
 		fs_subset_out_desc.bEndpointAddress;

 	status = usb_assign_descriptors(f, fs_eth_function, hs_eth_function,
 			ss_eth_function);
 	if (status)
 		goto fail;

 	/* NOTE:  all that is done without knowing or caring about
 	 * the network link ... which is unavailable to this code
 	 * until we're activated via set_alt().
 	 */

 	DBG(cdev, "CDC Subset: %s speed IN/%s OUT/%s\n",
 			gadget_is_superspeed(c->cdev->gadget) ? "super" :
 			gadget_is_dualspeed(c->cdev->gadget) ? "dual" : "full",
 			geth->port.in_ep->name, geth->port.out_ep->name);
 	return 0;

 fail:
 	usb_free_all_descriptors(f);
 	/* we might as well release our claims on endpoints */
 	if (geth->port.out_ep)
 		geth->port.out_ep->driver_data = NULL;
 	if (geth->port.in_ep)
 		geth->port.in_ep->driver_data = NULL;

 	ERROR(cdev, "%s: can't bind, err %d\n", f->name, status);

 	return status;
 }

 static inline struct f_gether_opts *to_f_gether_opts(struct config_item *item)
 {
 	return container_of(to_config_group(item), struct f_gether_opts,
 			    func_inst.group);
 }

 /* f_gether_item_ops */
 USB_ETHERNET_CONFIGFS_ITEM(gether);

 /* f_gether_opts_dev_addr */
 USB_ETHERNET_CONFIGFS_ITEM_ATTR_DEV_ADDR(gether);

 /* f_gether_opts_host_addr */
 USB_ETHERNET_CONFIGFS_ITEM_ATTR_HOST_ADDR(gether);

 /* f_gether_opts_qmult */
 USB_ETHERNET_CONFIGFS_ITEM_ATTR_QMULT(gether);

 /* f_gether_opts_ifname */
 USB_ETHERNET_CONFIGFS_ITEM_ATTR_IFNAME(gether);

 static struct configfs_attribute *gether_attrs[] = {
 	&f_gether_opts_dev_addr.attr,
 	&f_gether_opts_host_addr.attr,
 	&f_gether_opts_qmult.attr,
 	&f_gether_opts_ifname.attr,
 	NULL,
 };

 static struct config_item_type gether_func_type = {
 	.ct_item_ops	= &gether_item_ops,
 	.ct_attrs	= gether_attrs,
 	.ct_owner	= THIS_MODULE,
 };

 static void geth_free_inst(struct usb_function_instance *f)
 {
 	struct f_gether_opts *opts;

 	opts = container_of(f, struct f_gether_opts, func_inst);
 	if (opts->bound)
 		gether_cleanup(netdev_priv(opts->net));
 	else
 		free_netdev(opts->net);
 	kfree(opts);
 }

 static struct usb_function_instance *geth_alloc_inst(void)
 {
 	struct f_gether_opts *opts;

 	opts = kzalloc(sizeof(*opts), GFP_KERNEL);
 	if (!opts)
 		return ERR_PTR(-ENOMEM);
 	mutex_init(&opts->lock);
 	opts->func_inst.free_func_inst = geth_free_inst;
 	opts->net = gether_setup_default();
 	if (IS_ERR(opts->net)) {
 		struct net_device *net = opts->net;
 		kfree(opts);
 		return ERR_CAST(net);
 	}

 	config_group_init_type_name(&opts->func_inst.group, "",
 				    &gether_func_type);

 	return &opts->func_inst;
 }

 static void geth_free(struct usb_function *f)
 {
 	struct f_gether *eth;

 	eth = func_to_geth(f);
 	kfree(eth);
 }

 static void geth_unbind(struct usb_configuration *c, struct usb_function *f)
 {
 	geth_string_defs[0].id = 0;
 	usb_free_all_descriptors(f);
 }

 static struct usb_function *geth_alloc(struct usb_function_instance *fi)
 {
 	struct f_gether	*geth;
 	struct f_gether_opts *opts;
 	int status;

 	/* allocate and initialize one new instance */
 	geth = kzalloc(sizeof(*geth), GFP_KERNEL);
 	if (!geth)
 		return ERR_PTR(-ENOMEM);

 	opts = container_of(fi, struct f_gether_opts, func_inst);

 	mutex_lock(&opts->lock);
 	opts->refcnt++;
 	/* export host's Ethernet address in CDC format */
 	status = gether_get_host_addr_cdc(opts->net, geth->ethaddr,
 					  sizeof(geth->ethaddr));
 	if (status < 12) {
 		kfree(geth);
 		mutex_unlock(&opts->lock);
 		return ERR_PTR(-EINVAL);
 	}
 	geth_string_defs[1].s = geth->ethaddr;

 	geth->port.ioport = netdev_priv(opts->net);
 	mutex_unlock(&opts->lock);
 	geth->port.cdc_filter = DEFAULT_FILTER;

 	geth->port.func.name = "cdc_subset";
 	geth->port.func.bind = geth_bind;
 	geth->port.func.unbind = geth_unbind;
 	geth->port.func.set_alt = geth_set_alt;
 	geth->port.func.disable = geth_disable;
 	geth->port.func.free_func = geth_free;

 	return &geth->port.func;
 }

 DECLARE_USB_FUNCTION_INIT(geth, geth_alloc_inst, geth_alloc);
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("David Brownell");
	/*
	* f_subset.c -- "CDC Subset" Ethernet link function driver
	*
	* Copyright (C) 2003-2005,2008 David Brownell
	* Copyright (C) 2008 Nokia Corporation
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2 of the License, or
	* (at your option) any later version.
	*/

	#include <linux/slab.h>
	#include <linux/kernel.h>
	#include <linux/module.h>
	#include <linux/device.h>
	#include <linux/etherdevice.h>

	#include "u_ether.h"
	#include "u_ether_configfs.h"
	#include "u_gether.h"

	/*
	* This function packages a simple "CDC Subset" Ethernet port with no real
	* control mechanisms; just raw data transfer over two bulk endpoints.
	* The data transfer model is exactly that of CDC Ethernet, which is
	* why we call it the "CDC Subset".
	*
	* Because it's not standardized, this has some interoperability issues.
	* They mostly relate to driver binding, since the data transfer model is
	* so simple (CDC Ethernet). The original versions of this protocol used
	* specific product/vendor IDs: byteswapped IDs for Digital Equipment's
	* SA-1100 "Itsy" board, which could run Linux 2.4 kernels and supported
	* daughtercards with USB peripheral connectors. (It was used more often
	* with other boards, using the Itsy identifiers.) Linux hosts recognized
	* this with CONFIG_USB_ARMLINUX; these devices have only one configuration
	* and one interface.
	*
	* At some point, MCCI defined a (nonconformant) CDC MDLM variant called
	* "SAFE", which happens to have a mode which is identical to the "CDC
	* Subset" in terms of data transfer and lack of control model. This was
	* adopted by later Sharp Zaurus models, and by some other software which
	* Linux hosts recognize with CONFIG_USB_NET_ZAURUS.
	*
	* Because Microsoft's RNDIS drivers are far from robust, we added a few
	* descriptors to the CDC Subset code, making this code look like a SAFE
	* implementation. This lets you use MCCI's host side MS-Windows drivers
	* if you get fed up with RNDIS. It also makes it easier for composite
	* drivers to work, since they can use class based binding instead of
	* caring about specific product and vendor IDs.
	*/

	struct f_gether {
	struct gether port;

	char ethaddr[14];
	};

	static inline struct f_gether func_to_geth(struct usb_function f)
	{
	return container_of(f, struct f_gether, port.func);
	}

	/-------------------------------------------------------------------------/

	/*
	* "Simple" CDC-subset option is a simple vendor-neutral model that most
	* full speed controllers can handle: one interface, two bulk endpoints.
	* To assist host side drivers, we fancy it up a bit, and add descriptors so
	* some host side drivers will understand it as a "SAFE" variant.
	*
	* "SAFE" loosely follows CDC WMC MDLM, violating the spec in various ways.
	* Data endpoints live in the control interface, there's no data interface.
	* And it's not used to talk to a cell phone radio.
	*/

	/* interface descriptor: */

	static struct usb_interface_descriptor subset_data_intf = {
	.bLength = sizeof subset_data_intf,
	.bDescriptorType = USB_DT_INTERFACE,

	/* .bInterfaceNumber = DYNAMIC */
	.bAlternateSetting = 0,
	.bNumEndpoints = 2,
	.bInterfaceClass = USB_CLASS_COMM,
	.bInterfaceSubClass = USB_CDC_SUBCLASS_MDLM,
	.bInterfaceProtocol = 0,
	/* .iInterface = DYNAMIC */
	};

	static struct usb_cdc_header_desc mdlm_header_desc = {
	.bLength = sizeof mdlm_header_desc,
	.bDescriptorType = USB_DT_CS_INTERFACE,
	.bDescriptorSubType = USB_CDC_HEADER_TYPE,

	.bcdCDC = cpu_to_le16(0x0110),
	};

	static struct usb_cdc_mdlm_desc mdlm_desc = {
	.bLength = sizeof mdlm_desc,
	.bDescriptorType = USB_DT_CS_INTERFACE,
	.bDescriptorSubType = USB_CDC_MDLM_TYPE,

	.bcdVersion = cpu_to_le16(0x0100),
	.bGUID = {
	0x5d, 0x34, 0xcf, 0x66, 0x11, 0x18, 0x11, 0xd6,
	0xa2, 0x1a, 0x00, 0x01, 0x02, 0xca, 0x9a, 0x7f,
	},
	};

	/* since "usb_cdc_mdlm_detail_desc" is a variable length structure, we
	* can't really use its struct. All we do here is say that we're using
	* the submode of "SAFE" which directly matches the CDC Subset.
	*/
	static u8 mdlm_detail_desc[] = {
	6,
	USB_DT_CS_INTERFACE,
	USB_CDC_MDLM_DETAIL_TYPE,

	0, /* "SAFE" */
	0, /* network control capabilities (none) */
	0, /* network data capabilities ("raw" encapsulation) */
	};

	static struct usb_cdc_ether_desc ether_desc = {
	.bLength = sizeof ether_desc,
	.bDescriptorType = USB_DT_CS_INTERFACE,
	.bDescriptorSubType = USB_CDC_ETHERNET_TYPE,

	/* this descriptor actually adds value, surprise! */
	/* .iMACAddress = DYNAMIC */
	.bmEthernetStatistics = cpu_to_le32(0), /* no statistics */
	.wMaxSegmentSize = cpu_to_le16(ETH_FRAME_LEN),
	.wNumberMCFilters = cpu_to_le16(0),
	.bNumberPowerFilters = 0,
	};

	/* full speed support: */

	static struct usb_endpoint_descriptor fs_subset_in_desc = {
	.bLength = USB_DT_ENDPOINT_SIZE,
	.bDescriptorType = USB_DT_ENDPOINT,

	.bEndpointAddress = USB_DIR_IN,
	.bmAttributes = USB_ENDPOINT_XFER_BULK,
	};

	static struct usb_endpoint_descriptor fs_subset_out_desc = {
	.bLength = USB_DT_ENDPOINT_SIZE,
	.bDescriptorType = USB_DT_ENDPOINT,

	.bEndpointAddress = USB_DIR_OUT,
	.bmAttributes = USB_ENDPOINT_XFER_BULK,
	};

	static struct usb_descriptor_header *fs_eth_function[] = {
	(struct usb_descriptor_header *) &subset_data_intf,
	(struct usb_descriptor_header *) &mdlm_header_desc,
	(struct usb_descriptor_header *) &mdlm_desc,
	(struct usb_descriptor_header *) &mdlm_detail_desc,
	(struct usb_descriptor_header *) &ether_desc,
	(struct usb_descriptor_header *) &fs_subset_in_desc,
	(struct usb_descriptor_header *) &fs_subset_out_desc,
	NULL,
	};

	/* high speed support: */

	static struct usb_endpoint_descriptor hs_subset_in_desc = {
	.bLength = USB_DT_ENDPOINT_SIZE,
	.bDescriptorType = USB_DT_ENDPOINT,

	.bmAttributes = USB_ENDPOINT_XFER_BULK,
	.wMaxPacketSize = cpu_to_le16(512),
	};

	static struct usb_endpoint_descriptor hs_subset_out_desc = {
	.bLength = USB_DT_ENDPOINT_SIZE,
	.bDescriptorType = USB_DT_ENDPOINT,

	.bmAttributes = USB_ENDPOINT_XFER_BULK,
	.wMaxPacketSize = cpu_to_le16(512),
	};

	static struct usb_descriptor_header *hs_eth_function[] = {
	(struct usb_descriptor_header *) &subset_data_intf,
	(struct usb_descriptor_header *) &mdlm_header_desc,
	(struct usb_descriptor_header *) &mdlm_desc,
	(struct usb_descriptor_header *) &mdlm_detail_desc,
	(struct usb_descriptor_header *) &ether_desc,
	(struct usb_descriptor_header *) &hs_subset_in_desc,
	(struct usb_descriptor_header *) &hs_subset_out_desc,
	NULL,
	};

	/* super speed support: */

	static struct usb_endpoint_descriptor ss_subset_in_desc = {
	.bLength = USB_DT_ENDPOINT_SIZE,
	.bDescriptorType = USB_DT_ENDPOINT,

	.bmAttributes = USB_ENDPOINT_XFER_BULK,
	.wMaxPacketSize = cpu_to_le16(1024),
	};

	static struct usb_endpoint_descriptor ss_subset_out_desc = {
	.bLength = USB_DT_ENDPOINT_SIZE,
	.bDescriptorType = USB_DT_ENDPOINT,

	.bmAttributes = USB_ENDPOINT_XFER_BULK,
	.wMaxPacketSize = cpu_to_le16(1024),
	};

	static struct usb_ss_ep_comp_descriptor ss_subset_bulk_comp_desc = {
	.bLength = sizeof ss_subset_bulk_comp_desc,
	.bDescriptorType = USB_DT_SS_ENDPOINT_COMP,

	/* the following 2 values can be tweaked if necessary */
	/* .bMaxBurst = 0, */
	/* .bmAttributes = 0, */
	};

	static struct usb_descriptor_header *ss_eth_function[] = {
	(struct usb_descriptor_header *) &subset_data_intf,
	(struct usb_descriptor_header *) &mdlm_header_desc,
	(struct usb_descriptor_header *) &mdlm_desc,
	(struct usb_descriptor_header *) &mdlm_detail_desc,
	(struct usb_descriptor_header *) &ether_desc,
	(struct usb_descriptor_header *) &ss_subset_in_desc,
	(struct usb_descriptor_header *) &ss_subset_bulk_comp_desc,
	(struct usb_descriptor_header *) &ss_subset_out_desc,
	(struct usb_descriptor_header *) &ss_subset_bulk_comp_desc,
	NULL,
	};

	/* string descriptors: */

	static struct usb_string geth_string_defs[] = {
	[0].s = "CDC Ethernet Subset/SAFE",
	[1].s = "",
	{ } /* end of list */
	};

	static struct usb_gadget_strings geth_string_table = {
	.language = 0x0409, /* en-us */
	.strings = geth_string_defs,
	};

	static struct usb_gadget_strings *geth_strings[] = {
	&geth_string_table,
	NULL,
	};

	/-------------------------------------------------------------------------/

	static int geth_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
	{
	struct f_gether *geth = func_to_geth(f);
	struct usb_composite_dev *cdev = f->config->cdev;
	struct net_device *net;

	/* we know alt == 0, so this is an activation or a reset */

	if (geth->port.in_ep->driver_data) {
	DBG(cdev, "reset cdc subset\n");
	gether_disconnect(&geth->port);
	}

	DBG(cdev, "init + activate cdc subset\n");
	if (config_ep_by_speed(cdev->gadget, f, geth->port.in_ep) \|\|
	config_ep_by_speed(cdev->gadget, f, geth->port.out_ep)) {
	geth->port.in_ep->desc = NULL;
	geth->port.out_ep->desc = NULL;
	return -EINVAL;
	}

	net = gether_connect(&geth->port);
	return IS_ERR(net) ? PTR_ERR(net) : 0;
	}

	static void geth_disable(struct usb_function *f)
	{
	struct f_gether *geth = func_to_geth(f);
	struct usb_composite_dev *cdev = f->config->cdev;

	DBG(cdev, "net deactivated\n");
	gether_disconnect(&geth->port);
	}

	/-------------------------------------------------------------------------/

	/* serial function driver setup/binding */

	static int
	geth_bind(struct usb_configuration c, struct usb_function f)
	{
	struct usb_composite_dev *cdev = c->cdev;
	struct f_gether *geth = func_to_geth(f);
	struct usb_string *us;
	int status;
	struct usb_ep *ep;

	struct f_gether_opts *gether_opts;

	gether_opts = container_of(f->fi, struct f_gether_opts, func_inst);

	/*
	* in drivers/usb/gadget/configfs.c:configfs_composite_bind()
	* configurations are bound in sequence with list_for_each_entry,
	* in each configuration its functions are bound in sequence
	* with list_for_each_entry, so we assume no race condition
	* with regard to gether_opts->bound access
	*/
	if (!gether_opts->bound) {
	mutex_lock(&gether_opts->lock);
	gether_set_gadget(gether_opts->net, cdev->gadget);
	status = gether_register_netdev(gether_opts->net);
	mutex_unlock(&gether_opts->lock);
	if (status)
	return status;
	gether_opts->bound = true;
	}

	us = usb_gstrings_attach(cdev, geth_strings,
	ARRAY_SIZE(geth_string_defs));
	if (IS_ERR(us))
	return PTR_ERR(us);

	subset_data_intf.iInterface = us[0].id;
	ether_desc.iMACAddress = us[1].id;

	/* allocate instance-specific interface IDs */
	status = usb_interface_id(c, f);
	if (status < 0)
	goto fail;
	subset_data_intf.bInterfaceNumber = status;

	status = -ENODEV;

	/* allocate instance-specific endpoints */
	ep = usb_ep_autoconfig(cdev->gadget, &fs_subset_in_desc);
	if (!ep)
	goto fail;
	geth->port.in_ep = ep;
	ep->driver_data = cdev; /* claim */

	ep = usb_ep_autoconfig(cdev->gadget, &fs_subset_out_desc);
	if (!ep)
	goto fail;
	geth->port.out_ep = ep;
	ep->driver_data = cdev; /* claim */

	/* support all relevant hardware speeds... we expect that when
	* hardware is dual speed, all bulk-capable endpoints work at
	* both speeds
	*/
	hs_subset_in_desc.bEndpointAddress = fs_subset_in_desc.bEndpointAddress;
	hs_subset_out_desc.bEndpointAddress =
	fs_subset_out_desc.bEndpointAddress;

	ss_subset_in_desc.bEndpointAddress = fs_subset_in_desc.bEndpointAddress;
	ss_subset_out_desc.bEndpointAddress =
	fs_subset_out_desc.bEndpointAddress;

	status = usb_assign_descriptors(f, fs_eth_function, hs_eth_function,
	ss_eth_function);
	if (status)
	goto fail;

	/* NOTE: all that is done without knowing or caring about
	* the network link ... which is unavailable to this code
	* until we're activated via set_alt().
	*/

	DBG(cdev, "CDC Subset: %s speed IN/%s OUT/%s\n",
	gadget_is_superspeed(c->cdev->gadget) ? "super" :
	gadget_is_dualspeed(c->cdev->gadget) ? "dual" : "full",
	geth->port.in_ep->name, geth->port.out_ep->name);
	return 0;

	fail:
	usb_free_all_descriptors(f);
	/* we might as well release our claims on endpoints */
	if (geth->port.out_ep)
	geth->port.out_ep->driver_data = NULL;
	if (geth->port.in_ep)
	geth->port.in_ep->driver_data = NULL;

	ERROR(cdev, "%s: can't bind, err %d\n", f->name, status);

	return status;
	}

	static inline struct f_gether_opts to_f_gether_opts(struct config_item item)
	{
	return container_of(to_config_group(item), struct f_gether_opts,
	func_inst.group);
	}

	/* f_gether_item_ops */
	USB_ETHERNET_CONFIGFS_ITEM(gether);

	/* f_gether_opts_dev_addr */
	USB_ETHERNET_CONFIGFS_ITEM_ATTR_DEV_ADDR(gether);

	/* f_gether_opts_host_addr */
	USB_ETHERNET_CONFIGFS_ITEM_ATTR_HOST_ADDR(gether);

	/* f_gether_opts_qmult */
	USB_ETHERNET_CONFIGFS_ITEM_ATTR_QMULT(gether);

	/* f_gether_opts_ifname */
	USB_ETHERNET_CONFIGFS_ITEM_ATTR_IFNAME(gether);

	static struct configfs_attribute *gether_attrs[] = {
	&f_gether_opts_dev_addr.attr,
	&f_gether_opts_host_addr.attr,
	&f_gether_opts_qmult.attr,
	&f_gether_opts_ifname.attr,
	NULL,
	};

	static struct config_item_type gether_func_type = {
	.ct_item_ops = &gether_item_ops,
	.ct_attrs = gether_attrs,
	.ct_owner = THIS_MODULE,
	};

	static void geth_free_inst(struct usb_function_instance *f)
	{
	struct f_gether_opts *opts;

	opts = container_of(f, struct f_gether_opts, func_inst);
	if (opts->bound)
	gether_cleanup(netdev_priv(opts->net));
	else
	free_netdev(opts->net);
	kfree(opts);
	}

	static struct usb_function_instance *geth_alloc_inst(void)
	{
	struct f_gether_opts *opts;

	opts = kzalloc(sizeof(*opts), GFP_KERNEL);
	if (!opts)
	return ERR_PTR(-ENOMEM);
	mutex_init(&opts->lock);
	opts->func_inst.free_func_inst = geth_free_inst;
	opts->net = gether_setup_default();
	if (IS_ERR(opts->net)) {
	struct net_device *net = opts->net;
	kfree(opts);
	return ERR_CAST(net);
	}

	config_group_init_type_name(&opts->func_inst.group, "",
	&gether_func_type);

	return &opts->func_inst;
	}

	static void geth_free(struct usb_function *f)
	{
	struct f_gether *eth;

	eth = func_to_geth(f);
	kfree(eth);
	}

	static void geth_unbind(struct usb_configuration c, struct usb_function f)
	{
	geth_string_defs[0].id = 0;
	usb_free_all_descriptors(f);
	}

	static struct usb_function geth_alloc(struct usb_function_instance fi)
	{
	struct f_gether *geth;
	struct f_gether_opts *opts;
	int status;

	/* allocate and initialize one new instance */
	geth = kzalloc(sizeof(*geth), GFP_KERNEL);
	if (!geth)
	return ERR_PTR(-ENOMEM);

	opts = container_of(fi, struct f_gether_opts, func_inst);

	mutex_lock(&opts->lock);
	opts->refcnt++;
	/* export host's Ethernet address in CDC format */
	status = gether_get_host_addr_cdc(opts->net, geth->ethaddr,
	sizeof(geth->ethaddr));
	if (status < 12) {
	kfree(geth);
	mutex_unlock(&opts->lock);
	return ERR_PTR(-EINVAL);
	}
	geth_string_defs[1].s = geth->ethaddr;

	geth->port.ioport = netdev_priv(opts->net);
	mutex_unlock(&opts->lock);
	geth->port.cdc_filter = DEFAULT_FILTER;

	geth->port.func.name = "cdc_subset";
	geth->port.func.bind = geth_bind;
	geth->port.func.unbind = geth_unbind;
	geth->port.func.set_alt = geth_set_alt;
	geth->port.func.disable = geth_disable;
	geth->port.func.free_func = geth_free;

	return &geth->port.func;
	}

	DECLARE_USB_FUNCTION_INIT(geth, geth_alloc_inst, geth_alloc);
	MODULE_LICENSE("GPL");
	MODULE_AUTHOR("David Brownell");