RK3399中提供了USB gadget设备的支持，程序在内核中目录“kernel/drivers/usb/gadget”中，支持的设备如U盘、USB串口、USB网卡、USB键盘鼠标等等，RK3399主板上有6个USB接口，其中的type-c接口是USB OTG接口，既支持USB HOST也支持USB DEVICE设备，要使RK3399配置成一个USB gadget设备（比如配置成一个hid 键盘），就得在type-c上实现，实际中这个功能有广泛的应用，比如pc主机和RK3399进行数据通信，用此就是一种很好的方式，RK3399的USB type-c接口初始时被配置成 Firefly-RK3399和ADB Interface设备，如下图：
现在我们重新构建内核，把RK3399模拟成一个USB的HID键盘设备。分如下几个步骤进行：
1、构建RK3399内核构建环境
构建编译环境,参见：http://wiki.t-firefly.com/zh_CN/Firefly-RK3399/prepare_compile_android.html
官方推荐 Ubuntu 14.04 操作系统，我安装的是 Ubuntu 16.04.1 ，完全可以
安装android sdk：参见http://wiki.t-firefly.com/zh_CN/Firefly-RK3399/compile_android7.1_firmware.html
编译环境的构建和android sdk的配置是一个比较复杂的过程，配置过程中会出现很多奇奇怪怪的问题，好在网上资料较多， 仔细分析，一般都能解决。
2、修改hid.c文件，此文件在kernel/drivers/usb/gadget/legacy/目录下，增加以下内容：
（1）增加hidg_func_descriptor结构变量my_hid_data
static struct hidg_func_descriptor my_hid_data = {
.subclass = 0, /* No subclass */
.protocol = 1, /* Keyboard */
.report_length = 8,
.report_desc_length = 63,
.report_desc = {
0x05, 0x01, /* USAGE_PAGE (Generic Desktop) */
0x09, 0x06, /* USAGE (Keyboard) */
0xa1, 0x01, /* COLLECTION (Application) */
0x05, 0x07, /* USAGE_PAGE (Keyboard) */
0x19, 0xe0, /* USAGE_MINIMUM (Keyboard LeftControl) */
0x29, 0xe7, /* USAGE_MAXIMUM (Keyboard Right GUI) */
0x15, 0x00, /* LOGICAL_MINIMUM (0) */
0x25, 0x01, /* LOGICAL_MAXIMUM (1) */
0x75, 0x01, /* REPORT_SIZE (1) */
0x95, 0x08, /* REPORT_COUNT (8) */
0x81, 0x02, /* INPUT (Data,Var,Abs) */
0x95, 0x01, /* REPORT_COUNT (1) */
0x75, 0x08, /* REPORT_SIZE (8) */
0x81, 0x03, /* INPUT (Cnst,Var,Abs) */
0x95, 0x05, /* REPORT_COUNT (5) */
0x75, 0x01, /* REPORT_SIZE (1) */
0x05, 0x08, /* USAGE_PAGE (LEDs) */
0x19, 0x01, /* USAGE_MINIMUM (Num Lock) */
0x29, 0x05, /* USAGE_MAXIMUM (Kana) */
0x91, 0x02, /* OUTPUT (Data,Var,Abs) */
0x95, 0x01, /* REPORT_COUNT (1) */
0x75, 0x03, /* REPORT_SIZE (3) */
0x91, 0x03, /* OUTPUT (Cnst,Var,Abs) */
0x95, 0x06, /* REPORT_COUNT (6) */
0x75, 0x08, /* REPORT_SIZE (8) */
0x15, 0x00, /* LOGICAL_MINIMUM (0) */
0x25, 0x65, /* LOGICAL_MAXIMUM (101) */
0x05, 0x07, /* USAGE_PAGE (Keyboard) */
0x19, 0x00, /* USAGE_MINIMUM (Reserved) */
0x29, 0x65, /* USAGE_MAXIMUM (Keyboard Application) */
0x81, 0x00, /* INPUT (Data,Ary,Abs) */
0xc0 /* END_COLLECTION */
}
};
（2） 增加platform_device结构变量my_hid
static struct platform_device my_hid = {
.name = "hidg",
.id = 0,
.num_resources = 0,
.resource = 0,
.dev.platform_data = &my_hid_data,
};
（3）在hidg_init(void)函数中增加如下语句
status = platform_device_register(&my_hid);
if (status < 0) {
return status;
}
（4）在hidg_cleanup(void)函数中增加如下语句
platform_device_unregister(&my_hid);
修改后完整的hid.c文件如下：
/*
* hid.c -- HID Composite driver
*
* Based on multi.c
*
* Copyright (C) 2010 Fabien Chouteau <[email protected]>
*
* 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/kernel.h>
#include <linux/platform_device.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/usb/composite.h>
#include <linux/usb/g_hid.h>
#define DRIVER_DESC "HID Gadget"
#define DRIVER_VERSION "2010/03/16"
#include "u_hid.h"
/*-------------------------------------------------------------------------*/
#define HIDG_VENDOR_NUM 0x0525 /* XXX NetChip */
#define HIDG_PRODUCT_NUM 0xa4ac /* Linux-USB HID gadget */
/*-------------------------------------------------------------------------*/
struct hidg_func_node {
struct usb_function_instance *fi;
struct usb_function *f;
struct list_head node;
struct hidg_func_descriptor *func;
};
static LIST_HEAD(hidg_func_list);
/*dhl********************************************************************/
static struct hidg_func_descriptor my_hid_data = {
.subclass = 0, /* No subclass */
.protocol = 1, /* Keyboard */
.report_length = 8,
.report_desc_length = 63,
.report_desc = {
0x05, 0x01, /* USAGE_PAGE (Generic Desktop) */
0x09, 0x06, /* USAGE (Keyboard) */
0xa1, 0x01, /* COLLECTION (Application) */
0x05, 0x07, /* USAGE_PAGE (Keyboard) */
0x19, 0xe0, /* USAGE_MINIMUM (Keyboard LeftControl) */
0x29, 0xe7, /* USAGE_MAXIMUM (Keyboard Right GUI) */
0x15, 0x00, /* LOGICAL_MINIMUM (0) */
0x25, 0x01, /* LOGICAL_MAXIMUM (1) */
0x75, 0x01, /* REPORT_SIZE (1) */
0x95, 0x08, /* REPORT_COUNT (8) */
0x81, 0x02, /* INPUT (Data,Var,Abs) */
0x95, 0x01, /* REPORT_COUNT (1) */
0x75, 0x08, /* REPORT_SIZE (8) */
0x81, 0x03, /* INPUT (Cnst,Var,Abs) */
0x95, 0x05, /* REPORT_COUNT (5) */
0x75, 0x01, /* REPORT_SIZE (1) */
0x05, 0x08, /* USAGE_PAGE (LEDs) */
0x19, 0x01, /* USAGE_MINIMUM (Num Lock) */
0x29, 0x05, /* USAGE_MAXIMUM (Kana) */
0x91, 0x02, /* OUTPUT (Data,Var,Abs) */
0x95, 0x01, /* REPORT_COUNT (1) */
0x75, 0x03, /* REPORT_SIZE (3) */
0x91, 0x03, /* OUTPUT (Cnst,Var,Abs) */
0x95, 0x06, /* REPORT_COUNT (6) */
0x75, 0x08, /* REPORT_SIZE (8) */
0x15, 0x00, /* LOGICAL_MINIMUM (0) */
0x25, 0x65, /* LOGICAL_MAXIMUM (101) */
0x05, 0x07, /* USAGE_PAGE (Keyboard) */
0x19, 0x00, /* USAGE_MINIMUM (Reserved) */
0x29, 0x65, /* USAGE_MAXIMUM (Keyboard Application) */
0x81, 0x00, /* INPUT (Data,Ary,Abs) */
0xc0 /* END_COLLECTION */
}
};
/*dhl********************************************************************/
/*-------------------------------------------------------------------------*/
USB_GADGET_COMPOSITE_OPTIONS();
static struct usb_device_descriptor device_desc = {
.bLength = sizeof device_desc,
.bDescriptorType = USB_DT_DEVICE,
.bcdUSB = cpu_to_le16(0x0200),
/* .bDeviceClass = USB_CLASS_COMM, */
/* .bDeviceSubClass = 0, */
/* .bDeviceProtocol = 0, */
.bDeviceClass = USB_CLASS_PER_INTERFACE,
.bDeviceSubClass = 0,
.bDeviceProtocol = 0,
/* .bMaxPacketSize0 = f(hardware) */
/* Vendor and product id can be overridden by module parameters. */
.idVendor = cpu_to_le16(HIDG_VENDOR_NUM),
.idProduct = cpu_to_le16(HIDG_PRODUCT_NUM),
/* .bcdDevice = f(hardware) */
/* .iManufacturer = DYNAMIC */
/* .iProduct = DYNAMIC */
/* NO SERIAL NUMBER */
.bNumConfigurations = 1,
};
static const struct usb_descriptor_header *otg_desc[2];
/* string IDs are assigned dynamically */
static struct usb_string strings_dev[] = {
[USB_GADGET_MANUFACTURER_IDX].s = "",
[USB_GADGET_PRODUCT_IDX].s = DRIVER_DESC,
[USB_GADGET_SERIAL_IDX].s = "",
{ } /* end of list */
};
static struct usb_gadget_strings stringtab_dev = {
.language = 0x0409, /* en-us */
.strings = strings_dev,
};
static struct usb_gadget_strings *dev_strings[] = {
&stringtab_dev,
NULL,
};
/****************************** Configurations ******************************/
static int do_config(struct usb_configuration *c)
{
struct hidg_func_node *e, *n;
int status = 0;
if (gadget_is_otg(c->cdev->gadget)) {
c->descriptors = otg_desc;
c->bmAttributes |= USB_CONFIG_ATT_WAKEUP;
}
list_for_each_entry(e, &hidg_func_list, node) {
e->f = usb_get_function(e->fi);
if (IS_ERR(e->f))
goto put;
status = usb_add_function(c, e->f);
if (status < 0) {
usb_put_function(e->f);
goto put;
}
}
return 0;
put:
list_for_each_entry(n, &hidg_func_list, node) {
if (n == e)
break;
usb_remove_function(c, n->f);
usb_put_function(n->f);
}
return status;
}
static struct usb_configuration config_driver = {
.label = "HID Gadget",
.bConfigurationValue = 1,
/* .iConfiguration = DYNAMIC */
.bmAttributes = USB_CONFIG_ATT_SELFPOWER,
};
/****************************** Gadget Bind ******************************/
static int hid_bind(struct usb_composite_dev *cdev)
{
struct usb_gadget *gadget = cdev->gadget;
struct list_head *tmp;
struct hidg_func_node *n, *m;
struct f_hid_opts *hid_opts;
int status, funcs = 0;
list_for_each(tmp, &hidg_func_list)
funcs++;
if (!funcs)
return -ENODEV;
list_for_each_entry(n, &hidg_func_list, node) {
n->fi = usb_get_function_instance("hid");
if (IS_ERR(n->fi)) {
status = PTR_ERR(n->fi);
goto put;
}
hid_opts = container_of(n->fi, struct f_hid_opts, func_inst);
hid_opts->subclass = n->func->subclass;
hid_opts->protocol = n->func->protocol;
hid_opts->report_length = n->func->report_length;
hid_opts->report_desc_length = n->func->report_desc_length;
hid_opts->report_desc = n->func->report_desc;
}
/* Allocate string descriptor numbers ... note that string
* contents can be overridden by the composite_dev glue.
*/
status = usb_string_ids_tab(cdev, strings_dev);
if (status < 0)
goto put;
device_desc.iManufacturer = strings_dev[USB_GADGET_MANUFACTURER_IDX].id;
device_desc.iProduct = strings_dev[USB_GADGET_PRODUCT_IDX].id;
if (gadget_is_otg(gadget) && !otg_desc[0]) {
struct usb_descriptor_header *usb_desc;
usb_desc = usb_otg_descriptor_alloc(gadget);
if (!usb_desc)
goto put;
usb_otg_descriptor_init(gadget, usb_desc);
otg_desc[0] = usb_desc;
otg_desc[1] = NULL;
}
/* register our configuration */
status = usb_add_config(cdev, &config_driver, do_config);
if (status < 0)
goto free_otg_desc;
usb_composite_overwrite_options(cdev, &coverwrite);
dev_info(&gadget->dev, DRIVER_DESC ", version: " DRIVER_VERSION "\n");
return 0;
free_otg_desc:
kfree(otg_desc[0]);
otg_desc[0] = NULL;
put:
list_for_each_entry(m, &hidg_func_list, node) {
if (m == n)
break;
usb_put_function_instance(m->fi);
}
return status;
}
static int hid_unbind(struct usb_composite_dev *cdev)
{
struct hidg_func_node *n;
list_for_each_entry(n, &hidg_func_list, node) {
usb_put_function(n->f);
usb_put_function_instance(n->fi);
}
kfree(otg_desc[0]);
otg_desc[0] = NULL;
return 0;
}
static int hidg_plat_driver_probe(struct platform_device *pdev)
{
struct hidg_func_descriptor *func = dev_get_platdata(&pdev->dev);
struct hidg_func_node *entry;
if (!func) {
dev_err(&pdev->dev, "Platform data missing\n");
return -ENODEV;
}
entry = kzalloc(sizeof(*entry), GFP_KERNEL);
if (!entry)
return -ENOMEM;
entry->func = func;
list_add_tail(&entry->node, &hidg_func_list);
return 0;
}
static int hidg_plat_driver_remove(struct platform_device *pdev)
{
struct hidg_func_node *e, *n;
list_for_each_entry_safe(e, n, &hidg_func_list, node) {
list_del(&e->node);
kfree(e);
}
return 0;
}
/****************************** Some noise ******************************/
static struct usb_composite_driver hidg_driver = {
.name = "g_hid",
.dev = &device_desc,
.strings = dev_strings,
.max_speed = USB_SPEED_HIGH,
.bind = hid_bind,
.unbind = hid_unbind,
};
static struct platform_driver hidg_plat_driver = {
.remove = hidg_plat_driver_remove,
.driver = {
.name = "hidg",
},
};
/*dhl********************************************************************/
static struct platform_device my_hid = {
.name = "hidg",
.id = 0,
.num_resources = 0,
.resource = 0,
.dev.platform_data = &my_hid_data,
};
/*dhl********************************************************************/
MODULE_DESCRIPTION(DRIVER_DESC);
MODULE_AUTHOR("Fabien Chouteau, Peter Korsgaard");
MODULE_LICENSE("GPL");
static int __init hidg_init(void)
{
int status;
/*dhl********************************************************************/
printk("donghailin enter hid\n");
status = platform_device_register(&my_hid);
if (status < 0) {
return status;
}
/*dhl********************************************************************/
status = platform_driver_probe(&hidg_plat_driver,
hidg_plat_driver_probe);
if (status < 0)
return status;
status = usb_composite_probe(&hidg_driver);
if (status < 0){
platform_driver_unregister(&hidg_plat_driver);
return status;
}
return status;
}
module_init(hidg_init);
static void __exit hidg_cleanup(void)
{
usb_composite_unregister(&hidg_driver);
platform_driver_unregister(&hidg_plat_driver);
/*dhl*********************************************************************/
platform_device_unregister(&my_hid);
/*dhl*********************************************************************/
}
module_exit(hidg_cleanup);
用以上的hid.c文件替换 “kernel/drivers/usb/gadget/legacy/”下的hid.c文件即可
3、重新构建内核
（1）修改内核配置
进入 kernel目录，首先执行make ARCH=arm64 firefly_defconfig生成默认配置文件
执行make menuconfig命令，按如配置下路径修改内核配置
Device Drivers->USB support->USB Gadget support->具体配置如下图：
选择保存，配置保存到.config文件中。
（2）kernel目录下执行make clean命令
（3）kernel目录下执行make -j8 ARCH=arm64 rk3399-firefly.img命令
（4）安装新内核，如下图
点击执行重新烧入新的内核,重新启动RK3399后，通过bus hound查看，没有发现usb设备，如下图：
（5）安装内核模块
将生成的内核模块libcomposite.ko、usb_f_hid.ko、g_hid.ko三个文件拷贝到RK3399的/sdcard/目录下，然后按如下顺序，执行命令
insmod libcomposite.ko
insmod usb_f_hid.ko
insmod g_hid.ko
当执行完最后一条命令后，正常情况下，你会听到你的pc会有发现新设备的提示声，到此你就成功了。在看一下bus hound如下图：
进入RK3399的/dev/目录，查看会发现新生成的hidg0设备，执行命令echo “123”>/dev/hidg0，在bus hound上查看，如下图：