drivers/usb/gadget/config.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * usb/gadget/config.c -- simplify building config descriptors
 *
 * Copyright (C) 2003 David Brownell
 *
 * Ported to U-Boot by: Thomas Smits <ts.smits@gmail.com> and
 *                      Remy Bohmer <linux@bohmer.net>
 */

#include <asm/unaligned.h>
#include <linux/errno.h>
#include <linux/list.h>
#include <linux/string.h>

#include <linux/usb/ch9.h>
#include <linux/usb/gadget.h>

/**
 * usb_descriptor_fillbuf - fill buffer with descriptors
 * @buf: Buffer to be filled
 * @buflen: Size of buf
 * @src: Array of descriptor pointers, terminated by null pointer.
 *
 * Copies descriptors into the buffer, returning the length or a
 * negative error code if they can't all be copied.  Useful when
 * assembling descriptors for an associated set of interfaces used
 * as part of configuring a composite device; or in other cases where
 * sets of descriptors need to be marshaled.
 */
int
usb_descriptor_fillbuf(void *buf, unsigned buflen,
		const struct usb_descriptor_header **src)
{
	u8	*dest = buf;

	if (!src)
		return -EINVAL;

	/* fill buffer from src[] until null descriptor ptr */
	for (; NULL != *src; src++) {
		unsigned		len = (*src)->bLength;

		if (len > buflen)
			return -EINVAL;
		memcpy(dest, *src, len);
		buflen -= len;
		dest += len;
	}
	return dest - (u8 *)buf;
}

/**
 * usb_gadget_config_buf - builts a complete configuration descriptor
 * @config: Header for the descriptor, including characteristics such
 *	as power requirements and number of interfaces.
 * @desc: Null-terminated vector of pointers to the descriptors (interface,
 *	endpoint, etc) defining all functions in this device configuration.
 * @buf: Buffer for the resulting configuration descriptor.
 * @length: Length of buffer.  If this is not big enough to hold the
 *	entire configuration descriptor, an error code will be returned.
 *
 * This copies descriptors into the response buffer, building a descriptor
 * for that configuration.  It returns the buffer length or a negative
 * status code.  The config.wTotalLength field is set to match the length
 * of the result, but other descriptor fields (including power usage and
 * interface count) must be set by the caller.
 *
 * Gadget drivers could use this when constructing a config descriptor
 * in response to USB_REQ_GET_DESCRIPTOR.  They will need to patch the
 * resulting bDescriptorType value if USB_DT_OTHER_SPEED_CONFIG is needed.
 */
int usb_gadget_config_buf(
	const struct usb_config_descriptor	*config,
	void					*buf,
	unsigned				length,
	const struct usb_descriptor_header	**desc
)
{
	struct usb_config_descriptor		*cp = buf;
	int					len;

	/* config descriptor first */
	if (length < USB_DT_CONFIG_SIZE || !desc)
		return -EINVAL;
	/* config need not be aligned */
	memcpy(cp, config, sizeof(*cp));

	/* then interface/endpoint/class/vendor/... */
	len = usb_descriptor_fillbuf(USB_DT_CONFIG_SIZE + (u8 *)buf,
			length - USB_DT_CONFIG_SIZE, desc);
	if (len < 0)
		return len;
	len += USB_DT_CONFIG_SIZE;
	if (len > 0xffff)
		return -EINVAL;

	/* patch up the config descriptor */
	cp->bLength = USB_DT_CONFIG_SIZE;
	cp->bDescriptorType = USB_DT_CONFIG;
	put_unaligned_le16(len, &cp->wTotalLength);
	cp->bmAttributes |= USB_CONFIG_ATT_ONE;
	return len;
}