GPIO的驱动模型

一、概述
GPIO是嵌入式系统最简单、最常用的资源了，比如点亮LED，控制蜂鸣器，输出高低电平，检测按键，等等。GPIO分输入和输出，在davinci linux中，有关GPIO的最底层的寄存器驱动，\arch\arm\mach-davinci目录下的gpio.c，这个是寄存器级的驱动，搞过单片机MCU的朋友应该比较熟悉寄存器级的驱动。

GPIO的驱动主要就是读取GPIO口的状态，或者设置GPIO口的状态。就是这么简单，但是为了能够写好的这个驱动，在LINUX上作了一些软件上的分层。为了让其它驱动可以方便的操作到GPIO，在LINUX里实现了对GPIO操作的统一接口，这个接口实则上就是GPIO驱动的框架，具体的实现文件为gpiolib.c在配置内核的时候，我们必须使用CONFIG_GENERIC_GPIO这个宏来支持GPIO驱动。

GPIO是与硬件体系密切相关的，linux提供一个模型来让驱动统一处理GPIO，即各个板卡都有实现自己的gpio_chip控制模块：request, free, input,output, get,set,irq...然后把控制模块注册到内核中，这时会改变全局gpio数组：gpio_desc[]. 当用户请求gpio时，就会到这个数组中找到，并调用这个GPIO对应的gpio_chip的处理函数。gpio实现为一组可用的 gpio_chip, 由驱动传入对应 gpio的全局序号去 request, dataout ,datain, free. 这时会调用gpio_chip中具体的实现。
gpio是一组可控件的脚，由多个寄存器同时控制。通过设置对应的寄存器可以达到设置GPIO口对应状态与功能。数据状态，输入输出方向，清零，中断（那个边沿触发）， 一般是一组（bank）一组的。
寄存器读写函数: __raw_writel() __raw_writeb() __raw_readl() __raw_readb()

二、linux 中GPIO模型的结构
//表示一个gpio口，含对应的gpio_chip.
//对于每一个gpio，都有一个gpio描述符，这个描述符包含了这个gpio所属的控制器即chip和一些标志，label等
struct gpio_desc {
    struct gpio_chip    *chip;
    unsigned long    flags;
    /* flag symbols are bit numbers */
    #define FLAG_REQUESTED  0
    #define FLAG_IS_OUT     1
    #define FLAG_RESERVED   2
    #define FLAG_EXPORT     3 /* protected by sysfs_lock */
    #define FLAG_SYSFS      4 /* exported via /sys/class/gpio/control */
    #define FLAG_TRIG_FALL  5 /* trigger on falling edge */
    #define FLAG_TRIG_RISE  6 /* trigger on rising edge */
    #define FLAG_ACTIVE_LOW 7 /* sysfs value has active low */
    #define FLAG_OPEN_DRAIN 8 /* Gpio is open drain type */
    #define FLAG_OPEN_SOURCE 9 /* Gpio is open source type */

    #define ID_SHIFT        16 /* add new flags before this one */
    #define GPIO_FLAGS_MASK ((1 << ID_SHIFT) - 1)
    #define GPIO_TRIGGER_MASK (BIT(FLAG_TRIG_FALL) | BIT(FLAG_TRIG_RISE))

#ifdef CONFIG_DEBUG_FS
    const char    *label;
#endif
};
//采用了一个具有ARCH_NR_GPIOS大小的gpio描述符数组。这个描述符数组便代表了系统所有的gpio。
static struct gpio_desc gpio_desc[ARCH_NR_GPIOS];//ARCH_NR_GPIOS=144,即系统现在有144个GPIO口

//static struct davinci_gpio_controller chips[DIV_ROUND_UP(DAVINCI_N_GPIO, 32)];//将144个GPIO分成每32个一组
//一组GPIO控制器结构，例如GPIO0和GPIO1是一组(共32个GPIO口)，共用一组寄存器，所以GPIO0和GPIO1荷载一起用chips[0]来控制
///共有144个GPIO，分为4组（GPIO0~GPIO8），每组有2个banks(即GPIO0和GPIO1为1组)，每组最多可以有32个GPIO，每组的控制寄存器空间有10个。
struct davinci_gpio_controller {
    struct gpio_chip    chip;//每组对应的gpio_chip
    int            irq_base;//每组对应的中断
    spinlock_t        lock;//自旋锁
    void __iomem        *regs;//每组的寄存器地址
    void __iomem        *set_data;//设置数据寄存器地址
    void __iomem        *clr_data;//清除数据寄存器地址
    void __iomem        *in_data;//输入数据寄存器地址
};

//每一个davinci_gpio_controller结构都对应于一个gpio_chip结构，gpio_chip既可看成是davinci_gpio_controller结构的补充
//表示一个gpio controller.通过这个结构抽象化所有的GPIO源，而让板上其它的模块可以用相同的接口调用使用这些GPIO。
struct gpio_chip {
    const char    *label;
    struct device    *dev;
    struct module    *owner;
    int    (*request)(struct gpio_chip *chip,unsigned offset);//请求gpio
    void    *free)(struct gpio_chip *chip,unsigned offset);//释放gpio
    int    (*get_direction)(struct gpio_chip *chip,unsigned offset);
    int    (*direction_input)(struct gpio_chip *chip,unsigned offset);//配置gpio为输入，返回当前gpio状态
    int    (*get)(struct gpio_chip *chip,unsigned offset);//获取gpio的状态
    int    (*direction_output)(struct gpio_chip *chip,unsigned offset, int value);//配置gpio为输出，并设置为value
    int    (*set_debounce)(struct gpio_chip *chip,unsigned offset, unsigned debounce);//设置消抖动时间，尤其是gpio按键时有用
    void    (*set)(struct gpio_chip *chip,unsigned offset, int value);//设置gpio为value值
    int    (*to_irq)(struct gpio_chip *chip,unsigned offset);//把gpio号转换为中断号
    void    (*dbg_show)(struct seq_file *s,struct gpio_chip *chip);
    int    base;// 这个gpio控制器的gpio开始编号
    u16    ngpio;//这个gpio控制器说控制的gpio数
    const char    *const *names;
    unsigned    can_sleep:1;
    unsigned    exported:1;

#if defined(CONFIG_OF_GPIO)
    struct device_node *of_node;
    int of_gpio_n_cells;
    int (*of_xlate)(struct gpio_chip *gc,const struct of_phandle_args *gpiospec, u32 *flags);
#endif
#ifdef CONFIG_PINCTRL
    struct list_head pin_ranges;
#endif
};

//GPIO寄存器结构
struct davinci_gpio_regs {
    u32 dir; // gpio方向设置寄存器
    u32    out_data; // gpio设置为输出时，表示输出状态(0或1)
    u32    set_data; // gpio设置为输出时，用于输出高电平
    u32    clr_data; // gpio设置为输出时，用于输出低电平
    u32    in_data; // gpio设置为输入时，用于读取输入值
    u32    set_rising; // gpio中断上升沿触发设置
    u32    clr_rising; // gpio中断上升沿触发清除
    u32    set_falling; // gpio中断下降沿触发设置
    u32    clr_falling; // gpio中断下降沿触发清除
    u32    intstat; // gpio中断状态位，由硬件设置，可读取，写1时清除。
};

struct gpio {
    unsigned        gpio;//gpio号
    unsigned long   flags;//gpio标志
    const char *label;//gpio名
};

三、GPIO的初始化
1.首先设置GPIO的管脚复用寄存器
static __init void da850_evm_init(void)
{
    //.......
    ret = davinci_cfg_reg_list(da850_gpio_test_pins);
    if (ret)
        pr_warning("da850_evm_init: gpio test ping mux setup failed: %d\n", ret);
    //.......
}

2.根据板级结构的资源初始化chips数组，此函数在系统初始化时自动调用
static struct davinci_gpio_controller chips[DIV_ROUND_UP(DAVINCI_N_GPIO, 32)];//将144个GPIO分成每32个一组
static int __init davinci_gpio_setup(void)
{
    int i, base;
    unsigned ngpio;
    struct davinci_soc_info *soc_info = &davinci_soc_info;//板级资源结构
    struct davinci_gpio_regs *regs;

    if (soc_info->gpio_type != GPIO_TYPE_DAVINCI)//判断GPIO类型
        return 0;

    ngpio = soc_info->gpio_num;//GPIO数量144
    if (ngpio == 0) {
        pr_err("GPIO setup:  how many GPIOs?\n");
        return -EINVAL;
    }

    if (WARN_ON(DAVINCI_N_GPIO < ngpio))//DAVINCI_N_GPIO=144
        ngpio = DAVINCI_N_GPIO;

    gpio_base = ioremap(soc_info->gpio_base, SZ_4K);//将GPIO的寄存器物理基地址（#define DA8XX_GPIO_BASE        0x01e26000）映射到内存中
    if (WARN_ON(!gpio_base))
        return -ENOMEM;

    //共有144个GPIO，分为4组（GPIO0~GPIO8），每组有2个banks(即GPIO0和GPIO1为1组)，每组最多可以有32个GPIO，每组的控制寄存器空间有10个。
    //chips[0]--chips[4],base值为0,32,64,96,128,ngpio分别为：32,32,32,32,16
    for (i = 0, base = 0; base < ngpio; i++, base += 32) {
        chips[i].chip.label = "DaVinci";
        //设置操作函数
        chips[i].chip.direction_input = davinci_direction_in;
        chips[i].chip.get = davinci_gpio_get;
        chips[i].chip.direction_output = davinci_direction_out;
        chips[i].chip.set = davinci_gpio_set;

        chips[i].chip.base = base;//每一组开始的GPIO号
        //每组控制的GPIO个数，一般为32个
        chips[i].chip.ngpio = ngpio - base;
        if (chips[i].chip.ngpio > 32)
            chips[i].chip.ngpio = 32;

        spin_lock_init(&chips[i].lock);
        //找到这组GPIO的寄存器地址，初始化chips结构
        regs = gpio2regs(base);
        chips[i].regs = regs;//设置每组的寄存器
        chips[i].set_data = ?s->set_data;
        chips[i].clr_data = ?s->clr_data;
        chips[i].in_data = ?s->in_data;

        gpiochip_add(&chips[i].chip);//注册gpio_chip
    }
    //chips数组添加到板级资源中
    soc_info->gpio_ctlrs = chips;
    soc_info->gpio_ctlrs_num = DIV_ROUND_UP(ngpio, 32);

    davinci_gpio_irq_setup();//设置GPIO中断
    return 0;
}
pure_initcall(davinci_gpio_setup);//linux初始化时会自动调用

static struct davinci_gpio_regs __iomem __init *gpio2regs(unsigned gpio)
{
    void __iomem *ptr;

    //根据GPIO的基地址累加，其中基地址(gpio_base+0)是REVID(Revision ID Register)寄存器
    //(gpio_base+8)是BINTEN (GPIO Interrupt Per-Bank Enable Register)寄存器
    //所以第一组寄存器从基地址+0x10开始
    if (gpio < 32 * 1)
        ptr = gpio_base + 0x10;
    else if (gpio < 32 * 2)
        ptr = gpio_base + 0x38;
    else if (gpio < 32 * 3)
        ptr = gpio_base + 0x60;
    else if (gpio < 32 * 4)
        ptr = gpio_base + 0x88;
    else if (gpio < 32 * 5)
        ptr = gpio_base + 0xb0;
    else
        ptr = NULL;
    return ptr;
}

int gpiochip_add(struct gpio_chip *chip)
{
    unsigned long    flags;
    int        status = 0;
    unsigned    id;
    int        base = chip->base;

    //检测gpio的有效性，判断这组GPIO的起始号是否在有效范围内
    if ((!gpio_is_valid(base) || !gpio_is_valid(base + chip->ngpio - 1))&& base >= 0) {
        status = -EINVAL;
        goto fail;
    }

    spin_lock_irqsave(&gpio_lock, flags);

    //如果这组GPIO的起始号小于0，则动态的分配gpio的开始索引。
    if (base < 0) {
        base = gpiochip_find_base(chip->ngpio);//这个函数在gpiolib.c中，在gpio_desc[]中分配chip->ngpio个空间(从最后往前分配)，返回第一个index
        if (base < 0) {
            status = base;
            goto unlock;
        }
        chip->base = base;
    }

    //确保这些分配的gpio号没有被其他chip占用
    for (id = base; id < base + chip->ngpio; id++) {
        if (gpio_desc[id].chip != NULL) {
            status = -EBUSY;
            break;
        }
    }
    //填充gpio_desc，将该组内的每个GPIO口的gpio_desc结构和该组的控制结构chip联系起来
    if (status == 0) {
        for (id = base; id < base + chip->ngpio; id++) {
            gpio_desc[id].chip = chip;
            gpio_desc[id].flags = !chip->direction_input? (1 << FLAG_IS_OUT): 0;//设置GPIO口标志
        }
    }
    of_gpiochip_add(chip);

unlock:
    spin_unlock_irqrestore(&gpio_lock, flags);

    if (status)
        goto fail;

    status = gpiochip_export(chip);//与sysfs文件系统有关，这里不关心
    if (status)
        goto fail;

    return 0;
fail:
    /* failures here can mean systems won't boot... */
    pr_err("gpiochip_add: gpios %d..%d (%s) failed to register\n",chip->base, chip->base + chip->ngpio - 1,chip->label ? : "generic");
    return status;
}

四.gpio的申请
//所谓申请就是检测GPIO描述符desc->flags的FLAG_REQUESTED标志，已申请的话该标志是1，否则是0
//往往多个gpio作为一个数组来进行申请
int gpio_request_array(struct gpio *array, size_t num)
{
    int i, err;

    for (i = 0; i < num; i++, array++) {//遍历数组中的每一个GPIO，gpio是GPIO号，flags是输入输出标志等，label是其取一个名字
        err = gpio_request_one(array->gpio, array->flags, array->label);
        if (err)
            goto err_free;
    }
    return 0;

err_free:
    while (i--)
        gpio_free((--array)->gpio);
    return err;
}

int gpio_request_one(unsigned gpio, unsigned long flags, const char *label)
{
    int err;

    //gpio则为你要申请的哪一个管脚，label则是为其取一个名字。
    err = gpio_request(gpio, label);
    if (err)
        return err;

    if (flags & GPIOF_DIR_IN)//GPIO标志是输入
        err = gpio_direction_input(gpio);//设置管脚为输入
    else//GPIO标志是输出
        err = gpio_direction_output(gpio,(flags & GPIOF_INIT_HIGH) ? 1 : 0);//根据标志确定输出1还是0

    if (err)
        gpio_free(gpio);

    return err;
}

int gpio_request(unsigned gpio, const char *label)
{
    struct gpio_desc    *desc;
    struct gpio_chip    *chip;
    int            status = -EINVAL;
    unsigned long        flags;
    //屏蔽中断
    spin_lock_irqsave(&gpio_lock, flags);

    if (!gpio_is_valid(gpio))//判断是否有效，也就是参数的取值范围判断
        goto done;

    //根据GPIO号找到对应的GPIO描述符结构
    desc = &gpio_desc[gpio];
    chip = desc->chip;//找到该GPIO所在的组控制器
    if (chip == NULL)
        goto done;

    //计数加1
    if (!try_module_get(chip->owner))
        goto done;

    //这里测试并设置flags的第FLAG_REQUESTED位，如果没有被申请就返回该位的原值0
    if (test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0) {
        desc_set_label(desc, label ? : "?");//设置GPIO描述符结构desc的label字段
        status = 0;
    } else {
        status = -EBUSY;
        module_put(chip->owner);
        goto done;
    }

    if (chip->request) {/* chip->request may sleep */
        spin_unlock_irqrestore(&gpio_lock, flags);
        status = chip->request(chip, gpio - chip->base);
        spin_lock_irqsave(&gpio_lock, flags);

        if (status < 0) {
            desc_set_label(desc, NULL);
            module_put(chip->owner);
            clear_bit(FLAG_REQUESTED, &desc->flags);
        }
    }

done:
    if (status)
        pr_debug("gpio_request: gpio-%d (%s) status %d\n",gpio, label ? : "?", status);
    spin_unlock_irqrestore(&gpio_lock, flags);
    return status;
}

五.GPIO的操作
1.设置GPIO为输出或输入
int gpio_direction_input(unsigned gpio)
{
    unsigned long        flags;
    struct gpio_chip    *chip;
    struct gpio_desc    *desc = &gpio_desc[gpio];
    int            status = -EINVAL;

    spin_lock_irqsave(&gpio_lock, flags);

    //判断GPIO号是否有效
    if (!gpio_is_valid(gpio))
        goto fail;
    //找到GPIO对应的gpio_chip结构
    chip = desc->chip;
    if (!chip || !chip->get || !chip->direction_input)
        goto fail;

    //确保此GPIO是在此组内，chip->base是此组GPIO的起始号，chip->ngpio是此组GPIO的个数
    gpio -= chip->base;
    if (gpio >= chip->ngpio)
        goto fail;

    //确保GPIO已申请
    status = gpio_ensure_requested(desc, gpio);
    if (status < 0)
        goto fail;

    //到这里可以确保GPIO是有效的
    spin_unlock_irqrestore(&gpio_lock, flags);

    might_sleep_if(chip->can_sleep);
    //status=0
    if (status) {
        status = chip->request(chip, gpio);
        if (status < 0) {
            pr_debug("GPIO-%d: chip request fail, %d\n",chip->base + gpio, status);
            goto lose;
        }
    }
    //调用底层的已经设置过的操作，这里即davinci_direction_in
    status = chip->direction_input(chip, gpio);
    if (status == 0)//返回成功
        clear_bit(FLAG_IS_OUT, &desc->flags);//清除输出标志
lose:
    return status;
fail:
    spin_unlock_irqrestore(&gpio_lock, flags);
    if (status)
        pr_debug("%s: gpio-%d status %d\n",__func__, gpio, status);
    return status;
}

int gpio_direction_output(unsigned gpio, int value)
{
    //.........GPIO的检查，同上函数

    //调用底层的已经设置过的操作，这里即davinci_direction_out
    status = chip->direction_output(chip, gpio, value);
    if (status == 0)//返回成功
        set_bit(FLAG_IS_OUT, &desc->flags);//设置输出标志
lose:
    return status;
fail:
    spin_unlock_irqrestore(&gpio_lock, flags);
    if (status)
        pr_debug("%s: gpio-%d status %d\n",__func__, gpio, status);
    return status;
}

//根据前边对gpio_chip结构的初始化，会调用\arch\arm\mach-davinci\gpio.c里的函数
static int davinci_direction_in(struct gpio_chip *chip, unsigned offset)
{
    return __davinci_direction(chip, offset, false, 0);
}

static int davinci_direction_out(struct gpio_chip *chip, unsigned offset, int value)
{
    return __davinci_direction(chip, offset, true, value);
}

static inline int __davinci_direction(struct gpio_chip *chip,unsigned offset, bool out, int value)
{
    struct davinci_gpio_controller *d = chip2controller(chip);
    struct davinci_gpio_regs __iomem *g = d->regs;//找到此组GPIO的控制寄存器地址
    unsigned long flags;
    u32 temp;
    u32 mask = 1 << offset;

    spin_lock_irqsave(&d->lock, flags);
    temp = __raw_readl(&g->dir);//读出当前寄存器的输入输出方向

    if (out) {//为1设置输出
        temp &= ~mask;
        __raw_writel(mask, value ? &g->set_data : &g->clr_data);//确定是用于输出高电平还是输出低电平
    }
    else {//为0设置为输入
        temp |= mask;
    }
    __raw_writel(temp, &g->dir);//写入方向寄存器
    spin_unlock_irqrestore(&d->lock, flags);

    return 0;
}

2.获取gpio的状态
int __gpio_get_value(unsigned gpio)
{
    struct gpio_chip    *chip;

    chip = gpio_to_chip(gpio);
    WARN_ON(chip->can_sleep);
    return chip->get ? chip->get(chip, gpio - chip->base) : 0;//调用davinci_gpio_get
}

static int davinci_gpio_get(struct gpio_chip *chip, unsigned offset)
{
    struct davinci_gpio_controller *d = chip2controller(chip);
    struct davinci_gpio_regs __iomem *g = d->regs;

    return (1 << offset) & __raw_readl(&g->in_data);
}

3.设置GPIO的值
void __gpio_set_value(unsigned gpio, int value)
{
    struct gpio_chip    *chip;

    chip = gpio_to_chip(gpio);
    WARN_ON(chip->can_sleep);
    chip->set(chip, gpio - chip->base, value);//调用davinci_gpio_set
}

static void davinci_gpio_set(struct gpio_chip *chip, unsigned offset, int value)
{
    struct davinci_gpio_controller *d = chip2controller(chip);
    struct davinci_gpio_regs __iomem *g = d->regs;

    __raw_writel((1 << offset), value ? &g->set_data : &g->clr_data);
}

六、GPIO驱动编写
1.首先要申请GPIO口
2.注册设备
3.创建GPIO的sysfs相关文件
#define  GPIO_MAJOR    199           // major device NO.
#define  GPIO_MINOR    0             // minor device NO.
#define  DEVICE_NAME "omapl138_gpios" /*定义设备驱动的名字，或设备节点名称*/

#define SET_OUTPUT_LOW 0
#define SET_OUTPUT_HIGH 1
#define GET_VALUE 2
#define SET_INPUT 3

static struct class *gpio_class;
static struct gpio gpio_array[] =
{
    /*{ GPIO_TO_PIN(0, 0), GPIOF_OUT_INIT_LOW,     "RTU_WDI_SIGNAL" },will request fail*/
    { GPIO_TO_PIN(0, 1), GPIOF_OUT_INIT_HIGH, "RTU_PLC_BAK_IO1"},
    { GPIO_TO_PIN(0, 2), GPIOF_OUT_INIT_LOW,     "RTU_CHG_EN" },
    { GPIO_TO_PIN(0, 3), GPIOF_IN,         "RTU_CHG_PG" },
    { GPIO_TO_PIN(0, 5), GPIOF_IN,         "RTU_USB_OC_OUT" },
    { GPIO_TO_PIN(0, 6), GPIOF_OUT_INIT_LOW,     "RTU_RUN_IND_LED" },
    { GPIO_TO_PIN(1, 10), GPIOF_IN,         "RTU_TSC_BUSY"},
    { GPIO_TO_PIN(1, 11), GPIOF_IN,        "RTU_PENIRQn" },
    { GPIO_TO_PIN(1, 12), GPIOF_OUT_INIT_LOW, "RTU_uP_Q26x_RESET" },
    { GPIO_TO_PIN(1, 13), GPIOF_OUT_INIT_HIGH, "RTU_uP_GPRS_PWR_EN" },
    { GPIO_TO_PIN(1, 14), GPIOF_OUT_INIT_HIGH, "RTU_uP_Q26x_ON/OFF" },
    { GPIO_TO_PIN(2, 1), GPIOF_OUT_INIT_LOW, "RTU_PLC_Reset" },
    { GPIO_TO_PIN(2, 2), GPIOF_OUT_INIT_LOW, "RTU_PLC_T_Reg" },
    { GPIO_TO_PIN(2, 4), GPIOF_OUT_INIT_LOW, "RTU_PLC_BAK_IO2" },
    { GPIO_TO_PIN(2, 5), GPIOF_OUT_INIT_LOW, "RTU_RS485_RE" },
    { GPIO_TO_PIN(2, 15), GPIOF_OUT_INIT_HIGH, "RTU_CHPWR_CS" },
    { GPIO_TO_PIN(3, 9), GPIOF_OUT_INIT_HIGH, "RTU_RS485_DE" },
    { GPIO_TO_PIN(6, 1), GPIOF_OUT_INIT_HIGH, "RTU_uP_VPIF_CLKO3" },
    { GPIO_TO_PIN(6, 9), GPIOF_IN,         "RTU_KEY_IN2" },
    { GPIO_TO_PIN(6, 11), GPIOF_IN,        "RTU_ALARM_IN5" },
    { GPIO_TO_PIN(6, 15), GPIOF_OUT_INIT_HIGH,"RTU_uP_RESETOUTn" },
};

static int gpio_open(struct inode *inode,struct file *file)
{
    printk(KERN_WARNING"gpio open success!\n");
    return 0;
}

static int gpio_release(struct inode *inode, struct file *filp)
{
  printk (KERN_ALERT "Device gpio released\n");
  return 0;
}

static int gpio_read(struct file*f,char *dst,size_t size,loff_t*offset)
{
    unsigned char num;
    __copy_to_user(&num,dst,1);
#ifdef DEBUG
     printk("__copy_to_user:%d\n",num);
#endif

    return 0;
}

static int gpio_write(struct file*f,const char *src,size_t size,loff_t *offset)
{
     unsigned char num;
     __copy_from_user(&num,src,1);
#ifdef DEBUG
     printk("__copy_from_user:%d\n",num);
#endif
     return 0;

}

static long gpio_ioctl(struct file *file,unsigned int cmd,unsigned long gpio)
{
    int i;
    unsigned long gpio_num = (gpio/100)*16+gpio%100;
    for (i = 0; i < ARRAY_SIZE(gpio_array); i++) {
        if(gpio_array[i].gpio == gpio_num)
            goto valid_gpio;
    }
    return -1;

valid_gpio:
    switch(cmd)//cmd表示应用程序传入的 GPIO 动作
    {
        case SET_OUTPUT_LOW://0
        {
            gpio_direction_output(gpio_num, 0);
            break;
        }
        case SET_OUTPUT_HIGH://1
        {
            gpio_direction_output(gpio_num, 1);
            break;
        }
        case GET_VALUE://2
        {
            return gpio_get_value(gpio_num);
        }
        case SET_INPUT://3
        {
            gpio_direction_input(gpio_num);
            break;
        }
        default:
        {
            printk(KERN_EMERG "GPIO command mistake!!!\n");
            break;
        }
    }
    return 0;
}

static const struct file_operations gpio_fops =
{
  .owner = THIS_MODULE,
  .open = gpio_open,
  .release = gpio_release,
  .read = gpio_read,
  .write = gpio_write,
  .unlocked_ioctl = gpio_ioctl,
};

static int __init gpio_init(void) /*内核初始化会调用该函数*/
{
    int ret;

    ret = gpio_request_array(gpio_array, ARRAY_SIZE(gpio_array));
    if (ret < 0)
    {
        printk(KERN_EMERG "GPIO request failed\n");
        goto request_failed;
    }

    dev_t my_dev_no;
    struct cdev *gpio_cdev;
    gpio_cdev = cdev_alloc();
    if(gpio_cdev == NULL)
    {
        printk(KERN_EMERG "Cannot alloc cdev\n");
        goto request_failed;
    }
    cdev_init(gpio_cdev,&gpio_fops);
    gpio_cdev->owner=THIS_MODULE;
    int result=alloc_chrdev_region(&my_dev_no,0,1,DEVICE_NAME);
    if(result < 0)
    {
        printk(KERN_EMERG "alloc_chrdev_region failed\n");
        goto request_failed;
    }
    ret=cdev_add(gpio_cdev,my_dev_no,1);


  ret = register_chrdev(GPIO_MAJOR, DEVICE_NAME, &gpio_fops);//驱动字符设备
     if(ret < 0)
     {
    printk(KERN_EMERG "GPIO register failed\n");
    goto request_failed;
     }

    //在sysfs文件系统下创建一个类
  gpio_class = class_create(THIS_MODULE, DEVICE_NAME);
  //device_create-->device_create_vargs-->device_register创建相应的sysfs文件(如dev文件)，用于udev根据sysfs文件系统下的dev文件创建设备节点
    device_create(gpio_class, NULL, MKDEV(GPIO_MAJOR, GPIO_MINOR), NULL, DEVICE_NAME);
    return ret;

request_failed:
    gpio_free_array(gpio_array, ARRAY_SIZE(gpio_array));
    return ret;
}

static void __exit gpio_exit(void)
{
    device_destroy(gpio_class, MKDEV(GPIO_MAJOR, GPIO_MINOR));
  class_unregister(gpio_class);
  class_destroy(gpio_class);
  unregister_chrdev(GPIO_MAJOR, DEVICE_NAME);
}

module_init(gpio_init);
module_exit(gpio_exit);
MODULE_LICENSE("GPL");
MODULE_VERSION ("v2.0");
MODULE_AUTHOR("wbl <>");
MODULE_DESCRIPTION("OMAPL138 GPIO driver");