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 "); 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 ", 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 ", 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 ", 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 ", 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 ", 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 ", 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 }
主要是gpio的中断，定时器，工作队列等设置。没什么大问题。具体函数不懂，碰到一个查一个。
代分析码相对简单困了回去睡觉了。
参考：
GPIO按键的应用参考：http://gofayao.blog.163.com/blog/static/147305254201491631157686/
驱动代码分析：http://www.linuxidc.com/Linux/2011-11/47650p3.htm
谢谢！