linux系统下标准GPIO按键驱动

浏览数：45 / 时间：2015年06月20日

前言：

　　linux下platform平台驱动是为了方便隔离bsp与driver，利于移植。体现好代码的高内聚，低耦合。Linux设备驱动模型中，关心总线，设备和驱动三个实体。总线将设备和驱动绑定。在系统每注册一个设备的时候，都会寻找与之相匹配的驱动，相反的，每加载一个驱动的时候，也会寻找与之匹配的设备。匹配由总线完成。linux发明了一种虚拟的总线，称之为platform总线，相应的设备称之为platform_device，驱动为platform_driver。

　　基于这个模型，又根据面向对象的思想，同一类的事物定义为一个基类。因此在驱动中，将同一基类的驱动，再抽象一个核心层。因此又分为了input设备，I2C设备，SPI设备等驱动。我们今天说的标准按键驱动，就是基于input输入设备。

正题：

　　在内核中，按键的驱动已经完成！！！不需要我们自己写。driver/input/keyboard/gpio_keys.c 就是驱动文件。刚才说了，有驱动，还要有设备啊~只有这两个匹配了，只有这样我们才能在应用层操作这个设备。这个设备我们在哪注册呢？一般的，在板级的初始化c文件里面。比如：board_max6q_sabresd.c。这里面我们怎么搞呢？看下面：：：：：：

 1 #if defined(CONFIG_KEYBOARD_GPIO) || defined(CONFIG_KEYBOARD_GPIO_MODULE)
 2 #define GPIO_BUTTON(gpio_num, ev_code, act_low, descr, wake, debounce)     3 {                                 4     .gpio        = gpio_num,                 5     .type        = EV_KEY,                 6     .code        = ev_code,                 7     .active_low    = act_low,                 8     .desc        = "btn " descr,                 9     .wakeup        = wake,                    10     .debounce_interval = debounce,                11 }
12 
13 static struct gpio_keys_button imx6q_buttons[] = {
14     GPIO_BUTTON(SABRESD_KEY_USER1, KEY_VOLUMEUP, 1, "user-key-1", 0, 1),
15     GPIO_BUTTON(SABRESD_KEY_USER2, KEY_VOLUMEDOWN, 1, "user-key-2", 0, 1),
16     GPIO_BUTTON(SABRESD_KEY_WHIBUSB, KEY_F1, 1, "whibusb", 0, 1),
17     GPIO_BUTTON(SABRESD_KEY_WHIBUSL, KEY_F2, 1, "whibusl", 0, 1),
18     GPIO_BUTTON(SABRESD_KEY_WHIBUSR, KEY_F3, 1, "whibusr", 0, 1),
19 };
20 
21 static struct gpio_keys_platform_data imx6q_button_data = {
22     .buttons    = imx6q_buttons,
23     .nbuttons    = ARRAY_SIZE(imx6q_buttons),
24 };
25 
26 static struct platform_device imx6q_button_device = {
27     .name        = "gpio-keys",
28     .id        = -1,
29     .num_resources  = 0,
30     .dev        = {
31         .platform_data = &imx6q_button_data,
32     }
33 };
34 
35 static void __init imx6q_add_device_buttons(void)
36 {
37     platform_device_register(&imx6q_button_device);
38 }
39 #else
40 static void __init imx6q_add_device_buttons(void) {}
41 #endif

上面注册了5个按键设备。然后在board_init()初始化函数里面，添加imx6q_add_device_buttons()。我们就可以通过应用层操作了。比如：按下某个按键的时候，在read()函数中获取哪个键被按下。下面的链接360无死角的gpio按键应用。注意的是/dev/input/eventX不太一样，操作的时候可以cat /proc/bus/input/devices查看一下咱们的按键是哪个event。

　　看看上面的代码，依葫芦画瓢就可以完成GPIO按键的设备添加。接下来我们分析下驱动，能用了，最好还是明白下原理。

　　跟网上其他的差不多，我们着重分析两个函数：

  1 static int __devinit gpio_keys_probe(struct platform_device *pdev)
  2 {
  3     struct gpio_keys_platform_data *pdata = pdev->dev.platform_data;　　　　//相关的结构体以及宏定义在本c文件和include/linux/input.h include/linux/gpio_keys.h里面找。
  4     struct gpio_keys_drvdata *ddata;
  5     struct device *dev = &pdev->dev;
  6     struct input_dev *input;
  7     int i, error;
  8     int wakeup = 0;
  9 　　
 10     ddata = kzalloc(sizeof(struct gpio_keys_drvdata) +　　　　//分配且清空数据空间
 11             pdata->nbuttons * sizeof(struct gpio_button_data),
 12             GFP_KERNEL);
 13     input = input_allocate_device();　　　　//分配一个input设备
 14     if (!ddata || !input) {
 15         dev_err(dev, "failed to allocate state\n");
 16         error = -ENOMEM;
 17         goto fail1;
 18     }
 19 　　　　//设置input设备属性
 20     ddata->input = input;　　　　
 21     ddata->n_buttons = pdata->nbuttons;
 22     ddata->enable = pdata->enable;
 23     ddata->disable = pdata->disable;
 24     mutex_init(&ddata->disable_lock);
 25 
 26     platform_set_drvdata(pdev, ddata);
 27     input_set_drvdata(input, ddata);
 28 
 29     input->name = pdata->name ? : pdev->name;
 30     input->phys = "gpio-keys/input0";
 31     input->dev.parent = &pdev->dev;
 32     input->open = gpio_keys_open;
 33     input->close = gpio_keys_close;
 34 
 35     input->id.bustype = BUS_HOST;
 36     input->id.vendor = 0x0001;
 37     input->id.product = 0x0001;
 38     input->id.version = 0x0100;
 39 
 40     /* Enable auto repeat feature of Linux input subsystem */
 41     if (pdata->rep)
 42         __set_bit(EV_REP, input->evbit);
 43 
 44     for (i = 0; i < pdata->nbuttons; i++) {　　　　//对注册的每个gpio进行设置
 45         struct gpio_keys_button *button = &pdata->buttons[i];
 46         struct gpio_button_data *bdata = &ddata->data[i];
 47         unsigned int type = button->type ?: EV_KEY;
 48 
 49         bdata->input = input;
 50         bdata->button = button;
 51 
 52         error = gpio_keys_setup_key(pdev, bdata, button);　　　　//这个是具体实现，下面分析
 53         if (error)
 54             goto fail2;
 55 
 56         if (button->wakeup)
 57             wakeup = 1;
 58　　　　　　/*设置设备对事件的支持，比如设置对键1和键2的支持*/ 
 59         input_set_capability(input, type, button->code);
 60     }
 61 　　//创建文件系统的节点，可以网上搜搜看，好像我之前的博文也有写到这块
 62     error = sysfs_create_group(&pdev->dev.kobj, &gpio_keys_attr_group);
 63     if (error) {
 64         dev_err(dev, "Unable to export keys/switches, error: %d\n",
 65             error);
 66         goto fail2;
 67     }
 68 　　//注册一个input设备
 69     error = input_register_device(input);
 70     if (error) {
 71         dev_err(dev, "Unable to register input device, error: %d\n",
 72             error);
 73         goto fail3;
 74     }
 75 
 76     /* get current state of buttons */
 77     for (i = 0; i < pdata->nbuttons; i++)
 78         gpio_keys_report_event(&ddata->data[i]);
 79     input_sync(input);
 80 
 81     device_init_wakeup(&pdev->dev, wakeup);
 82 
 83     return 0;
 84 
 85  fail3:
 86     sysfs_remove_group(&pdev->dev.kobj, &gpio_keys_attr_group);
 87  fail2:
 88     while (--i >= 0) {
 89         free_irq(gpio_to_irq(pdata->buttons[i].gpio), &ddata->data[i]);
 90         if (ddata->data[i].timer_debounce)
 91             del_timer_sync(&ddata->data[i].timer);
 92         cancel_work_sync(&ddata->data[i].work);
 93         gpio_free(pdata->buttons[i].gpio);
 94     }
 95 
 96     platform_set_drvdata(pdev, NULL);
 97  fail1:
 98     input_free_device(input);
 99     kfree(ddata);
100 
101     return error;
102 }

上面是probe函数的一些简要说明，probe顾名思义，就是探测到设备注册时，驱动完成的工作。

下面的函数是probe里面重要的gpio_keys_setup_key（）函数

 1 static int __devinit gpio_keys_setup_key(struct platform_device *pdev,
 2                      struct gpio_button_data *bdata,
 3                      struct gpio_keys_button *button)
 4 {
 5     const char *desc = button->desc ? button->desc : "gpio_keys";
 6     struct device *dev = &pdev->dev;
 7     unsigned long irqflags;
 8     int irq, error;
 9 
10     setup_timer(&bdata->timer, gpio_keys_timer, (unsigned long)bdata);
11     INIT_WORK(&bdata->work, gpio_keys_work_func);
12 
13     error = gpio_request(button->gpio, desc);
14     if (error < 0) {
15         dev_err(dev, "failed to request GPIO %d, error %d\n",
16             button->gpio, error);
17         goto fail2;
18     }
19 
20     error = gpio_direction_input(button->gpio);
21     if (error < 0) {
22         dev_err(dev, "failed to configure"
23             " direction for GPIO %d, error %d\n",
24             button->gpio, error);
25         goto fail3;
26     }
27 
28     if (button->debounce_interval) {
29         error = gpio_set_debounce(button->gpio,
30                       button->debounce_interval * 1000);
31         /* use timer if gpiolib doesn‘t provide debounce */
32         if (error < 0)
33             bdata->timer_debounce = button->debounce_interval;
34     }
35 
36     irq = gpio_to_irq(button->gpio);
37     if (irq < 0) {
38         error = irq;
39         dev_err(dev, "Unable to get irq number for GPIO %d, error %d\n",
40             button->gpio, error);
41         goto fail3;
42     }
43 
44     irqflags = IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING;
45     /*
46      * If platform has specified that the button can be disabled,
47      * we don‘t want it to share the interrupt line.
48      */
49     if (!button->can_disable)
50         irqflags |= IRQF_SHARED;
51     /*
52      * If platform has specified that the button can wake up the system,
53      * for example, the power key which usually use to wake up the system
54      * from suspend, we add the IRQF_EARLY_RESUME flag to this irq, so
55      * that the power key press can be handled and reported as early as
56      * possible. Some platform like Android need to get the power key
57      * event early to reume some devcies like framebuffer and etc.
58      */
59     if (button->wakeup)
60         irqflags |= IRQF_EARLY_RESUME;
61 
62     error = request_any_context_irq(irq, gpio_keys_isr, irqflags, desc, bdata);
63     if (error < 0) {
64         dev_err(dev, "Unable to claim irq %d; error %d\n",
65             irq, error);
66         goto fail3;
67     }
68 
69     return 0;
70 
71 fail3:
72     gpio_free(button->gpio);
73 fail2:
74     return error;
75 }