BACKPORT: usb: gadget: add raw-gadget interface

==============

USB Raw Gadget

==============

USB Raw Gadget is a kernel module that provides a userspace interface for

the USB Gadget subsystem. Essentially it allows to emulate USB devices

from userspace. Enabled with CONFIG_USB_RAW_GADGET. Raw Gadget is

currently a strictly debugging feature and shouldn't be used in

production, use GadgetFS instead.

Comparison to GadgetFS

~~~~~~~~~~~~~~~~~~~~~~

Raw Gadget is similar to GadgetFS, but provides a more low-level and

direct access to the USB Gadget layer for the userspace. The key

differences are:

1. Every USB request is passed to the userspace to get a response, while

   GadgetFS responds to some USB requests internally based on the provided

   descriptors. However note, that the UDC driver might respond to some

   requests on its own and never forward them to the Gadget layer.

2. GadgetFS performs some sanity checks on the provided USB descriptors,

   while Raw Gadget allows you to provide arbitrary data as responses to

   USB requests.

3. Raw Gadget provides a way to select a UDC device/driver to bind to,

   while GadgetFS currently binds to the first available UDC.

4. Raw Gadget uses predictable endpoint names (handles) across different

   UDCs (as long as UDCs have enough endpoints of each required transfer

   type).

5. Raw Gadget has ioctl-based interface instead of a filesystem-based one.

Userspace interface

~~~~~~~~~~~~~~~~~~~

To create a Raw Gadget instance open /dev/raw-gadget. Multiple raw-gadget

instances (bound to different UDCs) can be used at the same time. The

interaction with the opened file happens through the ioctl() calls, see

comments in include/uapi/linux/usb/raw_gadget.h for details.

The typical usage of Raw Gadget looks like:

1. Open Raw Gadget instance via /dev/raw-gadget.

2. Initialize the instance via USB_RAW_IOCTL_INIT.

3. Launch the instance with USB_RAW_IOCTL_RUN.

4. In a loop issue USB_RAW_IOCTL_EVENT_FETCH calls to receive events from

   Raw Gadget and react to those depending on what kind of USB device

   needs to be emulated.

Potential future improvements

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

- Implement ioctl's for setting/clearing halt status on endpoints.

- Reporting more events (suspend, resume, etc.) through

  USB_RAW_IOCTL_EVENT_FETCH.

- Support O_NONBLOCK I/O.

	  Say "y" to link the driver statically, or "m" to build a

	  dynamically linked module called "g_webcam".

config USB_RAW_GADGET

	tristate "USB Raw Gadget"

	help

	  USB Raw Gadget is a kernel module that provides a userspace interface

	  for the USB Gadget subsystem. Essentially it allows to emulate USB

	  devices from userspace. See Documentation/usb/raw-gadget.rst for

	  details.

	  Say "y" to link the driver statically, or "m" to build a

	  dynamically linked module called "raw_gadget".

endchoice

obj-$(CONFIG_USB_G_NCM)		+= g_ncm.o

obj-$(CONFIG_USB_G_ACM_MS)	+= g_acm_ms.o

obj-$(CONFIG_USB_GADGET_TARGET)	+= tcm_usb_gadget.o

obj-$(CONFIG_USB_RAW_GADGET)	+= raw_gadget.o

/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */

/*

 * USB Raw Gadget driver.

 *

 * See Documentation/usb/raw-gadget.rst for more details.

 */

#ifndef _UAPI__LINUX_USB_RAW_GADGET_H

#define _UAPI__LINUX_USB_RAW_GADGET_H

#include <asm/ioctl.h>

#include <linux/types.h>

#include <linux/usb/ch9.h>

/* Maximum length of driver_name/device_name in the usb_raw_init struct. */

#define UDC_NAME_LENGTH_MAX 128

/*

 * struct usb_raw_init - argument for USB_RAW_IOCTL_INIT ioctl.

 * @speed: The speed of the emulated USB device, takes the same values as

 *     the usb_device_speed enum: USB_SPEED_FULL, USB_SPEED_HIGH, etc.

 * @driver_name: The name of the UDC driver.

 * @device_name: The name of a UDC instance.

 *

 * The last two fields identify a UDC the gadget driver should bind to.

 * For example, Dummy UDC has "dummy_udc" as its driver_name and "dummy_udc.N"

 * as its device_name, where N in the index of the Dummy UDC instance.

 * At the same time the dwc2 driver that is used on Raspberry Pi Zero, has

 * "20980000.usb" as both driver_name and device_name.

 */

struct usb_raw_init {

	__u8	driver_name[UDC_NAME_LENGTH_MAX];

	__u8	device_name[UDC_NAME_LENGTH_MAX];

	__u8	speed;

};

/* The type of event fetched with the USB_RAW_IOCTL_EVENT_FETCH ioctl. */

enum usb_raw_event_type {

	USB_RAW_EVENT_INVALID = 0,

	/* This event is queued when the driver has bound to a UDC. */

	USB_RAW_EVENT_CONNECT = 1,

	/* This event is queued when a new control request arrived to ep0. */

	USB_RAW_EVENT_CONTROL = 2,

	/* The list might grow in the future. */

};

/*

 * struct usb_raw_event - argument for USB_RAW_IOCTL_EVENT_FETCH ioctl.

 * @type: The type of the fetched event.

 * @length: Length of the data buffer. Updated by the driver and set to the

 *     actual length of the fetched event data.

 * @data: A buffer to store the fetched event data.

 *

 * Currently the fetched data buffer is empty for USB_RAW_EVENT_CONNECT,

 * and contains struct usb_ctrlrequest for USB_RAW_EVENT_CONTROL.

 */

struct usb_raw_event {

	__u32		type;

	__u32		length;

	__u8		data[0];

};

#define USB_RAW_IO_FLAGS_ZERO	0x0001

#define USB_RAW_IO_FLAGS_MASK	0x0001

static int usb_raw_io_flags_valid(__u16 flags)

{

	return (flags & ~USB_RAW_IO_FLAGS_MASK) == 0;

}

static int usb_raw_io_flags_zero(__u16 flags)

{

	return (flags & USB_RAW_IO_FLAGS_ZERO);

}

/*

 * struct usb_raw_ep_io - argument for USB_RAW_IOCTL_EP0/EP_WRITE/READ ioctls.

 * @ep: Endpoint handle as returned by USB_RAW_IOCTL_EP_ENABLE for

 *     USB_RAW_IOCTL_EP_WRITE/READ. Ignored for USB_RAW_IOCTL_EP0_WRITE/READ.

 * @flags: When USB_RAW_IO_FLAGS_ZERO is specified, the zero flag is set on

 *     the submitted USB request, see include/linux/usb/gadget.h for details.

 * @length: Length of data.

 * @data: Data to send for USB_RAW_IOCTL_EP0/EP_WRITE. Buffer to store received

 *     data for USB_RAW_IOCTL_EP0/EP_READ.

 */

struct usb_raw_ep_io {

	__u16		ep;

	__u16		flags;

	__u32		length;

	__u8		data[0];

};

/*

 * Initializes a Raw Gadget instance.

 * Accepts a pointer to the usb_raw_init struct as an argument.

 * Returns 0 on success or negative error code on failure.

 */

#define USB_RAW_IOCTL_INIT		_IOW('U', 0, struct usb_raw_init)

/*

 * Instructs Raw Gadget to bind to a UDC and start emulating a USB device.

 * Returns 0 on success or negative error code on failure.

 */

#define USB_RAW_IOCTL_RUN		_IO('U', 1)

/*

 * A blocking ioctl that waits for an event and returns fetched event data to

 * the user.

 * Accepts a pointer to the usb_raw_event struct.

 * Returns 0 on success or negative error code on failure.

 */

#define USB_RAW_IOCTL_EVENT_FETCH	_IOR('U', 2, struct usb_raw_event)

/*

 * Queues an IN (OUT for READ) urb as a response to the last control request

 * received on endpoint 0, provided that was an IN (OUT for READ) request and

 * waits until the urb is completed. Copies received data to user for READ.

 * Accepts a pointer to the usb_raw_ep_io struct as an argument.

 * Returns length of trasferred data on success or negative error code on

 * failure.

 */

#define USB_RAW_IOCTL_EP0_WRITE		_IOW('U', 3, struct usb_raw_ep_io)

#define USB_RAW_IOCTL_EP0_READ		_IOWR('U', 4, struct usb_raw_ep_io)

/*

 * Finds an endpoint that supports the transfer type specified in the

 * descriptor and enables it.

 * Accepts a pointer to the usb_endpoint_descriptor struct as an argument.

 * Returns enabled endpoint handle on success or negative error code on failure.

 */

#define USB_RAW_IOCTL_EP_ENABLE		_IOW('U', 5, struct usb_endpoint_descriptor)

/* Disables specified endpoint.

 * Accepts endpoint handle as an argument.

 * Returns 0 on success or negative error code on failure.

 */

#define USB_RAW_IOCTL_EP_DISABLE	_IOW('U', 6, __u32)

/*

 * Queues an IN (OUT for READ) urb as a response to the last control request

 * received on endpoint usb_raw_ep_io.ep, provided that was an IN (OUT for READ)

 * request and waits until the urb is completed. Copies received data to user

 * for READ.

 * Accepts a pointer to the usb_raw_ep_io struct as an argument.

 * Returns length of trasferred data on success or negative error code on

 * failure.

 */

#define USB_RAW_IOCTL_EP_WRITE		_IOW('U', 7, struct usb_raw_ep_io)

#define USB_RAW_IOCTL_EP_READ		_IOWR('U', 8, struct usb_raw_ep_io)

/*

 * Switches the gadget into the configured state.

 * Returns 0 on success or negative error code on failure.

 */

#define USB_RAW_IOCTL_CONFIGURE		_IO('U', 9)

/*

 * Constrains UDC VBUS power usage.

 * Accepts current limit in 2 mA units as an argument.

 * Returns 0 on success or negative error code on failure.

 */

#define USB_RAW_IOCTL_VBUS_DRAW		_IOW('U', 10, __u32)

#endif /* _UAPI__LINUX_USB_RAW_GADGET_H */