一、Linux驱动分层思想    

1.设备与驱动分离思想

        和设备相关的信息放到设备树里，驱动里面只写对于设备的操作方法

2.驱动分层思想

        把相同的操作提出来，构建子系统，子系统可以完成这些通用的操作（GPIO，引脚）

二、pinctrl子系统(linux内核中自带该系统)

        我们通过设备树来使用pinctrl子系统。pinctrl子系统中有2个概念：
                pin controller（一种引脚的定义和实现）：它对应IOMUX来复用引脚
                client device（使用某种引脚定义方向）：pinctrl子系统的客户，即使用pinctrl系统的设备。

        在imx6ull-alientek-emmc.dts文件中iomuxc节点中定义controller引脚配置

pinctrl_putekey: putekey {
fsl,pins = <MX6UL_PAD_UART1_CTS_B__GPIO1_IO18 0xf0b0>;
};

        在对应的putekey节点中引用该方案

putekey {
#address-cells = <1>;
#size-cells = <1>;
compatible = "pute-key";
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_putekey>;
reg = <0x209C004 0x4
0x209C000 0x4>;
status = "okay";
};

三、gpio子系统

在设备中指定节点使用的GPIO引脚编号

1. 在设备中指定节点使用的GPIO引脚编号,格式如下：

putekey {
#address-cells = <1>;
#size-cells = <1>;
compatible = "pute-key";
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_putekey>;
gpio-key = <&gpio1 18 GPIO_ACTIVE_LOW>;
status = "okay";
};

在putekey节点里面修改

2. 在驱动中编写代码

        2.1.通过of_get_named_gpio从设备树节点中解析并获取指定GPIO硬件编号

        2.2.通过gpio_request申请GPIO资源

        2.3.通过gpio_direction_input/output设置GPIO的方向

        2.4.通过gpio_get_value 读取输入引脚电平
                gpio_set_value设置输出引脚电平

        2.5.释放GPIO，gpio_free()

四、代码

以key为例

        pinctrl子系统

 pinctrl_putekey: putekey {
      fsl,pins = <MX6UL_PAD_UART1_CTS_B__GPIO1_IO18 0XF0B0>;
          };  

        gpio子系统

putekey {
          #address-cells = <1>;
          #size-cells = <1>;
          compatible = "pute-key";
          pinctrl-names = "default";
          pinctrl-0 = <&pinctrl_putekey>;
          gpio-key = <&gpio1 18 GPIO_ACTIVE_LOW>;
          status = "okay";
      };

        key_app.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>

int main(void)
{
    int fd = 0;
    int stat = 0;

    fd = open("/dev/misc_key", O_RDWR);
    if (-1 == fd)
    {
        perror("fail to open");
        return -1;
    }

    while (1)
    {
        read(fd, &stat, sizeof(stat));
        printf("stat = %d\n", stat);
    }

    close(fd);

    return 0;
}

        Makefile

#模块名
modulename := key_app

#编译工具链
CC := arm-linux-gnueabihf-gcc 

all:
	$(CC) $(modulename).c -o $(modulename)
	cp $(modulename) ~/nfs/rootfs 

.PHONY:
clean:
	rm $(modulename)
distclean:
	rm $(modulename)
	rm ~/nfs/rootfs/$(modulename)

        key_drv.c

#include <linux/init.h>
#include <linux/cdev.h>
#include <linux/fs.h>
#include <linux/module.h>
#include <linux/miscdevice.h>
#include <linux/of_address.h>
#include <linux/of.h>
#include <asm/uaccess.h>
#include <asm/io.h>
#include <linux/of_gpio.h>
#include <linux/gpio.h>

static struct device_node *pkeynode = NULL;
static int gpiokey = 0;

static ssize_t key_read(struct file *fp, char __user *puser, size_t n, loff_t *off)
{
    int status = 0;
    unsigned long nret = 0;

    if (gpio_get_value(gpiokey)) {
        status = 0;
    } else {
        status = 1;
    }

    nret = copy_to_user(puser, &status, sizeof(status));
    if (nret) {
        pr_info("copy_to_user failed\n");
        return -1;
    }

    return nret;
}

static struct file_operations fops = {
    .owner = THIS_MODULE,
    .read = key_read,
};

static struct miscdevice misc_key = {
    .minor = MISC_DYNAMIC_MINOR,
    .name = "misc_key",
    .fops = &fops,
};

static __init int key_drv_init(void)
{
    int ret = 0;
    
    ret = misc_register(&misc_key);
    if (ret) {
        pr_info("misc_register failed\n");
        return -1;
    }

    pkeynode = of_find_node_by_path("/putekey");
    if (NULL == pkeynode) {
        pr_info("of_find_node_by_path failed\n");
        return -1;
    }

    gpiokey = of_get_named_gpio(pkeynode, "gpio-key", 0);
    if (gpiokey < 0) {
        pr_info("of_get_named_gpio failed\n");
        return -1;
    }

    ret = gpio_request(gpiokey, "pute-key-gpio");
    if (ret) {
        pr_info("gpio_request failed\n");
        return -1;
    }

    ret = gpio_direction_input(gpiokey);
    if (ret) {
        pr_info("gpio_direction_input failed\n");
        return -1;
    }

    pr_info("key_drv_init success\n");

    return 0;
}

static __exit void key_drv_exit(void)
{
    int ret = 0;
    
    gpio_free(gpiokey);
    ret = misc_deregister(&misc_key);
    if (ret) {
        pr_info("misc_deregister failed\n");
        return;
    }

    pr_info("key_drv_exit success\n");

    return;
}

module_init(key_drv_init);
module_exit(key_drv_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("pute");

        Makefile

#模块名
modulename := key_drv

#内核路径
kerdir := /home/linux/imx6ull/kernel/linux-imx-rel_imx_4.1.15_2.1.0_ga_alientek

#加入内核编译中
obj-m += $(modulename).o

#当前路径
pwd := $(shell pwd)

all:
	make -C $(kerdir) modules M=$(pwd)
	cp $(modulename).ko ~/nfs/rootfs 

.PHONY:
clean:
	make -C $(kerdir) modules M=$(pwd) clean
distclean:
	make -C $(kerdir) modules M=$(pwd) clean
	rm ~/nfs/rootfs/$(modulename).ko

        Makefile

#模块名
modulename := key

all:
	make -C $(modulename)_drv
	make -C $(modulename)_app

.PHONY:
distclean:
	make -C $(modulename)_drv distclean
	make -C $(modulename)_app distclean 
clean:
	make -C $(modulename)_drv clean
	make -C $(modulename)_app clean