switch_gpio

创建玩一个switch类之后，最普通的用法就是把一个GPIO端口，用作一个switch信号，所以switch_gpio.c就这么诞生了，这是我的理解，不一定正确。

1.两个相关的数据结构：

struct gpio_switch_platform_data {
        const char *name;
        unsigned     gpio;
        /* if NULL, switch_dev.name will be printed */
        const char *name_on;
        const char *name_off;
        /* if NULL, "0" or "1" will be printed */
        const char *state_on;
        const char *state_off;
    };

    struct gpio_switch_data {
        struct switch_dev sdev;
        unsigned gpio;
        const char *name_on;
        const char *name_off;
        const char *state_on;
        const char *state_off;
        int irq;
        struct work_struct work;
    };

static struct platform_driver gpio_switch_driver = {
        .probe        = gpio_switch_probe,
        .remove        = __devexit_p(gpio_switch_remove),
        .driver        = {
            .name    = "switch-gpio",
            .owner    = THIS_MODULE,
        },
    };
    static int __init gpio_switch_init(void)
    {
        return platform_driver_register(&gpio_switch_driver);   //把gpio_switch注册成一个platform驱动。
    }
    static void __exit gpio_switch_exit(void)
    {
        platform_driver_unregister(&gpio_switch_driver);
    }
    module_init(gpio_switch_init);
    module_exit(gpio_switch_exit);

3. probe/remove

static int gpio_switch_probe(struct platform_device *pdev)
    {
        struct gpio_switch_platform_data *pdata = pdev->dev.platform_data;  //pdev包含的设备的platform专有数据,这种platform_data会在boar_i2c_info结构体中声明。
        struct gpio_switch_data *switch_data;
        int ret = 0;
        if (!pdata)
            return -EBUSY;
        switch_data = kzalloc(sizeof(struct gpio_switch_data), GFP_KERNEL);
        if (!switch_data)
            return -ENOMEM;
        switch_data->sdev.name = pdata->name;          //把外面声明的pdata内容，赋给switch_data
        switch_data->gpio = pdata->gpio;
        switch_data->name_on = pdata->name_on;
        switch_data->name_off = pdata->name_off;
        switch_data->state_on = pdata->state_on;
        switch_data->state_off = pdata->state_off;
        switch_data->sdev.print_state = switch_gpio_print_state;
        ret = switch_dev_register(&switch_data->sdev);   //向switch class中注册一个switch设备。
        if (ret < 0)
            goto err_switch_dev_register;
        ret = gpio_request(switch_data->gpio, pdev->name);   //获得gpio
        if (ret < 0)
            goto err_request_gpio;
        ret = gpio_direction_input(switch_data->gpio);   //定义gpio输入为输入信号
        if (ret < 0)
            goto err_set_gpio_input;
        INIT_WORK(&switch_data->work, gpio_switch_work);   //初始化一个工作队列gpio_switch_work()
        switch_data->irq = gpio_to_irq(switch_data->gpio);  //获得中断gpio
        if (switch_data->irq < 0) {
            ret = switch_data->irq;
            goto err_detect_irq_num_failed;
        }
        ret = request_irq(switch_data->irq, gpio_irq_handler,
                 IRQF_TRIGGER_LOW, pdev->name, switch_data);   //注册一个中断，
                                                               //中断号为switch_data->irq，
                                                               //中断处理程序为gpio_irq_handler(),
                                                               //中断类型为IRQF_TRIGGER_LOW
                                                               //中断设备名pdev->name
                                                               //中断设备地址switch_data
        if (ret < 0)
            goto err_request_irq;
        /* Perform initial detection */
        gpio_switch_work(&switch_data->work);
        return 0;
    err_request_irq:
    err_detect_irq_num_failed:
    err_set_gpio_input:
        gpio_free(switch_data->gpio);
    err_request_gpio:
        switch_dev_unregister(&switch_data->sdev);
    err_switch_dev_register:
        kfree(switch_data);
        return ret;
    }
    static int __devexit gpio_switch_remove(struct platform_device *pdev)
    {
        struct gpio_switch_data *switch_data = platform_get_drvdata(pdev);
        cancel_work_sync(&switch_data->work);
        gpio_free(switch_data->gpio);
        switch_dev_unregister(&switch_data->sdev);
        kfree(switch_data);
        return 0;
    }

static void gpio_switch_work(struct work_struct *work)
    {
        int state;
        struct gpio_switch_data    *data =
            container_of(work, struct gpio_switch_data, work);  //通过work，来获得gpio_switch_data的地址
        state = gpio_get_value(data->gpio);
        switch_set_state(&data->sdev, state);                   //设置state
    }
    static irqreturn_t gpio_irq_handler(int irq, void *dev_id)
    {
        struct gpio_switch_data *switch_data =
         (struct gpio_switch_data *)dev_id;
        schedule_work(&switch_data->work);                     //通过 工作队列 来处理
        return IRQ_HANDLED;
    }
    static ssize_t switch_gpio_print_state(struct switch_dev *sdev, char *buf)
    {
        struct gpio_switch_data    *switch_data =
            container_of(sdev, struct gpio_switch_data, sdev);
        const char *state;
        if (switch_get_state(sdev))
            state = switch_data->state_on;
        else
            state = switch_data->state_off;
        if (state)
            return sprintf(buf, "%s\n", state);              //输出state
        return -1;
    }