https://www.linuxidc.com/Linux/2016-10/136247.htm
设备模型(device-model)之平台总线（bus），驱动（driver），设备（device）
| [日期：2016-10-23] | 来源：Linux社区 作者：hackfun | [字体：[大](javascript:ContentSize(16)) [中](javascript:ContentSize(0)) [小](javascript:ContentSize(12))] |
关于关于驱动设备模型相关概念请参考《Linux Device Drivers》等相关书籍，和内核源码目录...\Documentation\driver-model
Linux Device Drivers [PDF] 下载见 http://www.linuxidc.com/Linux/2011-06/37778.htm
简单来说总线（bus），驱动（driver），设备（device）这三者之间的关系就是：驱动开发者可以通过总线（bus）来将驱动（driver）和设备（device）进行隔离，这样的好处就是开发者可以将相对稳定不变的驱动（driver）独立起来，可以通过总线（bus）来桥接与之匹配的设备（device）。设备（device）只需要提供与硬件相关的底层硬件的配置，如io,中断等。
platform.c 提供了一个平台总线（platform_bus）,和注册平台设备（platform_device）和平台驱动（platform_driver）的相关接口，其中平台总线（platform_bus）已经编进内核，开发者只需要提供平台设备（platform_device）和平台驱动（platform_driver）的相关代码就行了。
在linux源码目录\drivers\input\keyboard下，提供了一个gpio_keys.c的平台驱动（platform_driver）,这个就是一个简单地按键驱动，检测到按键状态，上报给输入子系统。
因此，开发者需要做的就是提供一个平台设备（platform_device），以向平台驱动（platform_driver）提供相关的硬件配置，如按键IO，中断号，按键码等等。
gpio_keys.c （不用任何改动）
/*
- Driver for keys on GPIO lines capable of generating interrupts.
- Copyright 2005 Phil Blundell
- This program is free software; you can redistribute it and/or modify
- it under the terms of the GNU General Public License version 2 as
- published by the Free Software Foundation.
*/
include
include
include
include
include
include
include
include
include
include
include
include
include
include
include
include
static irqreturn_t gpio_keys_isr(int irq, void dev_id)
{
int i;
/ [cgw]: 在gpio_keys_probe()中调用了request_irq(..., pdev),
* 因此dev_id指向了platform_device *pdev，通过dev_id间接传递
* platform_device *指针
*/
struct platform_device pdev = dev_id;
/ [cgw]: 当platform_device 和 platform_driver匹配时，会通过
* probe()传递platform_device进来。在注册platform_device时，
* platform_device.dev.platform_data必须指向gpio_keys_platform_data *
*/
struct gpio_keys_platform_data pdata = pdev->dev.platform_data;
/ [cgw]: probe()中已分配了一个struct input_dev，并通过platform_set_drvdata()
* 设置platform_device->dev->driver_data = input;
*/
struct input_dev *input = platform_get_drvdata(pdev);
/* [cgw]: 轮询pdata->nbuttons个按键 */
for (i = 0; i < pdata->nbuttons; i++) {
struct gpio_keys_button *button = &pdata->buttons[i];
int gpio = button->gpio;
/* [cgw]: 某个gpio发生了中断 */
if (irq == gpio_to_irq(gpio)) {
/* [cgw]: 获得按键类型 */
unsigned int type = button->type ?: EV_KEY;
/* [cgw]: 获取按键状态 */
int state = (gpio_get_value(gpio) ? 1 : 0) ^ button->active_low;
/* [cgw]: 发送按键事件 */
input_event(input, type, button->code, !!state);
/* [cgw]: 发送同步事件 */
input_sync(input);
}
}
return IRQ_HANDLED;
}
static int __devinit gpio_keys_probe(struct platform_device pdev)
{
/ [cgw]: 在gpio_keys_probe()中调用了request_irq(..., pdev),
* 因此dev_id指向了platform_device *pdev，通过dev_id间接传递
* platform_device *指针
*/
struct gpio_keys_platform_data *pdata = pdev->dev.platform_data;
struct input_dev *input;
int i, error;
/* [cgw]: 分配一个输入设备 */
input = input_allocate_device();
/* [cgw]: 分配失败 */
if (!input)
return -ENOMEM;
/* [cgw]: 设置platform_device->dev->driver_data = input */
platform_set_drvdata(pdev, input);
/* [cgw]: 设置evdev.c支持的事件类型 */
input->evbit[0] = BIT(EV_KEY);
/* [cgw]: 设置输入设备名，同platform_device的名字 */
input->name = pdev->name;
/* [cgw]: */
input->phys = "gpio-keys/input0";
/* [cgw]: 设置输入设备dev的父节点为platform_device->dev */
input->dev.parent = &pdev->dev;
/* [cgw]: 设置输入设备总线类型，供应商，产品，版本 */
input->id.bustype = BUS_HOST;
input->id.vendor = 0x0001;
input->id.product = 0x0001;
input->id.version = 0x0100;
/* [cgw]: 为pdata->nbuttons个按键申请中断 */
for (i = 0; i < pdata->nbuttons; i++) {
struct gpio_keys_button *button = &pdata->buttons[i];
/* [cgw]: 获得gpio对应的中断号 */
int irq = gpio_to_irq(button->gpio);
/* [cgw]: 获得按键类型 */
unsigned int type = button->type ?: EV_KEY;
/* [cgw]: 设置中断类型为边沿中断 */
set_irq_type(irq, IRQ_TYPE_EDGE_BOTH);
/* [cgw]: 申请中断，设置中断服务程序 */
error = request_irq(irq, gpio_keys_isr, IRQF_SAMPLE_RANDOM,
button->desc ? button->desc : "gpio_keys",
pdev);
if (error) {
printk(KERN_ERR "gpio-keys: unable to claim irq %d; error %d\n",
irq, error);
goto fail;
}
/* [cgw]: 设置evdev.c支持的按键码 */
input_set_capability(input, type, button->code);
}
/* [cgw]: 注册一个输入设备 */
error = input_register_device(input);
/* [cgw]: 注册失败 */
if (error) {
printk(KERN_ERR "Unable to register gpio-keys input device\n");
goto fail;
}
return 0;
fail:
/* [cgw]: 释放中断 /
for (i = i - 1; i >= 0; i--)
free_irq(gpio_to_irq(pdata->buttons[i].gpio), pdev);
/ [cgw]: 释放输入设备占用的内存 */
input_free_device(input);
return error;
}
static int __devexit gpio_keys_remove(struct platform_device pdev)
{
/ [cgw]: 在gpio_keys_probe()中调用了request_irq(..., pdev),
* 因此dev_id指向了platform_device *pdev，通过dev_id间接传递
* platform_device *指针
*/
struct gpio_keys_platform_data pdata = pdev->dev.platform_data;
/ [cgw]: probe()中已分配了一个struct input_dev，并通过platform_set_drvdata()
* 设置platform_device->dev->driver_data = input;
*/
struct input_dev *input = platform_get_drvdata(pdev);
int i;
/* [cgw]: 释放中断 */
for (i = 0; i < pdata->nbuttons; i++) {
int irq = gpio_to_irq(pdata->buttons[i].gpio);
free_irq(irq, pdev);
}
/* [cgw]: 注销输入设备 */
input_unregister_device(input);
return 0;
}
struct platform_driver gpio_keys_device_driver = {
.probe = gpio_keys_probe,
.remove = __devexit_p(gpio_keys_remove),
.driver = {
.name = "gpio-keys",
}
};
static int __init gpio_keys_init(void)
{
/* [cgw]: 注册gpio_keys_device_driver平台驱动 */
return platform_driver_register(&gpio_keys_device_driver);
}
static void __exit gpio_keys_exit(void)
{
/* [cgw]: 注销gpio_keys_device_driver平台驱动 */
platform_driver_unregister(&gpio_keys_device_driver);
}
module_init(gpio_keys_init);
module_exit(gpio_keys_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Phil Blundell [email protected]");
MODULE_DESCRIPTION("Keyboard driver for CPU GPIOs");
平台设备（platform_device）：
keys_dev.c
include
include
include
include
include
include
include
include
include
include
include
include
include
include
include
include
include
/* [cgw]: 设置四个按键的键码，按键io，激活状态，按键名，按键类型 */
static struct gpio_keys_button keys_buff[4] = {
{
KEY_A,
S3C2410_GPF0,
1,
"A",
EV_KEY
},
{
KEY_B,
S3C2410_GPF2,
1,
"B",
EV_KEY
},
{
KEY_C,
S3C2410_GPG3,
1,
"C",
EV_KEY
},
{
KEY_D,
S3C2410_GPG11,
1,
"D",
EV_KEY
},
};
static struct gpio_keys_platform_data keys_dev = {
.buttons = &keys_buff[0],
.nbuttons = ARRAY_SIZE(keys_buff)
};
static void keys_dev_release(struct device * dev)
{
printk("keys_dev_release! \n");
}
/* [cgw]: 分配一个平台设备 */
static struct platform_device keys_platform_dev = {
.name = "gpio-keys",
.id = -1,
.dev = {
.release = keys_dev_release,
.platform_data = (void *)&keys_dev,
},
};
static int keys_dev_init(void)
{
/* [cgw]: 注册keys_platform_dev平台设备 */
platform_device_register(&keys_platform_dev);
return 0;
}
static void keys_dev_exit(void)
{
/* [cgw]: 注销keys_platform_dev平台设备 */
platform_device_unregister(&keys_platform_dev);
}
module_init(keys_dev_init);
module_exit(keys_dev_exit);
MODULE_LICENSE("GPL");
应用测试程序:
platform_test.c
include
include
include
include
include
include
include
include
include
include
int fd;
void my_signal_fun(int signum)
{
struct input_event buttons_event;
/* [cgw]: 异步通知产生时返回的数据 */
read(fd, &buttons_event, sizeof(struct input_event));
/* [cgw]: 打印事件类型，事件码，事件值 */
printf("type: 0x%x code: 0x%x value: 0x%x\n",
buttons_event.type,
buttons_event.code,
buttons_event.value);
}
int main(int argc, char **argv)
{
int ret, arg;
struct pollfd fds[1];
unsigned long ver = 0;
fd = open("/dev/event1", O_RDWR | O_NONBLOCK);
if (fd < 0)
{
printf("can't open!\n");
}
ioctl(fd, EVIOCGVERSION, &ver);
printf("Ver:0x%x \n", ver);
/* [cgw]: 设置文件标识符 */
fds[0].fd = fd;
/* [cgw]: 设置应用程序要响应的事件 */
fds[0].events = POLLIN;
while (1)
{
/* [cgw]: 休眠5S */
ret = poll(fds, 1, 5000);
/* [cgw]: 唤醒或超时 */
//printf("wake up!\n");
if (ret == 0)
{
printf("time out\n");
}
else
{
my_signal_fun(arg);
}
}
close(fd);
return 0;
}
平台设备（platform_device） keys_platform_dev 是怎样找到与之匹配的平台驱动（platform_driver） gpio_keys_device_driver的呢？
因为他们都注册到了平台总线（platform_bus）上。平台驱动（platform_driver）和平台设备（platform_device）会相互查找彼此是否匹配，匹配的条件就是，
1 static int platform_match(struct device * dev, struct device_driver * drv) 2 { 3 struct platform_device *pdev = container_of(dev, struct platform_device, dev); 4
5 return (strncmp(pdev->name, drv->name, BUS_ID_SIZE) == 0); 6 }
platform_device->name == platform_driver->driver->name 即他们的名字就是：“gpio-keys”
一旦匹配，就会调用
static int platform_drv_probe(struct device *_dev)
{
struct platform_driver *drv = to_platform_driver(_dev->driver);
struct platform_device *dev = to_platform_device(_dev);
return drv->probe(dev);
}
drv->probe() = platform_driver->probe() = gpio_keys_probe()
这样平台驱动（platform_driver）就可以获得平台设备（platform_device）的 struct platform_device结构的数据了，即keys_platform_dev，从这个结构就可以获得相关配置，以使能平台驱动（platform_driver） gpio_keys.c中相应的IO和中断。
实验现象：
# insmod gpio_keys.ko //安装平台驱动（platform_driver）insmod keys_dev.ko //安装平台设备（platform_device）
input: gpio-keys as /class/input/input1
./platform_test //运行应用测试程序
Ver:0x10000 //用ioctl获取输入子系统的版本号
type: 0x1 code: 0x2e value: 0x1 //按下"C"键 type: 0x0 code: 0x0 value: 0x0 //因为调用了input_sync（） type: 0x1 code: 0x2e value: 0x0 //松开（弹起）"C"键 type: 0x0 code: 0x0 value: 0x0 //因为调用了input_sync（） type: 0x1 code: 0x30 value: 0x1 //... ... type: 0x0 code: 0x0 value: 0x0 type: 0x1 code: 0x30 value: 0x0 type: 0x0 code: 0x0 value: 0x0 type: 0x1 code: 0x1e value: 0x1 type: 0x0 code: 0x0 value: 0x0 type: 0x1 code: 0x1e value: 0x0 type: 0x0 code: 0x0 value: 0x0 type: 0x1 code: 0x20 value: 0x1 type: 0x0 code: 0x0 value: 0x0 type: 0x1 code: 0x20 value: 0x0 type: 0x0 code: 0x0 value: 0x0 time out time out time out
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