gpio导出，以及模块之间变量可见模块驱动实例

一 驱动实例

#include <linux/delay.h>#include <linux/if_arp.h>#include <linux/if_ether.h>#include <linux/interrupt.h>#include <linux/io.h>#include <linux/kernel.h>#include <linux/list.h>#include <linux/module.h>#include <linux/of.h>#include <linux/of_device.h>#include <linux/platform_device.h>#include <linux/gpio.h>#include <linux/irq.h>#include <linux/miscdevice.h>#include <linux/suspend.h>#include <linux/poll.h>/*GPIO3_3：用于检测串口是否出现overrun状态*/#define SERIAL_STATES_GPIO  67/*导出符号让其他内核模块可见，然后还需要在相应的.h文件中声明（extern volatile unsigned long serial_states;）*/volatile unsigned long serial_states;EXPORT_SYMBOL_GPL(serial_states);static int serial_states_open(struct inode *inode, struct file *file){    return 0;}static int serial_states_release(struct inode *inode, struct file *file){    /*note: releasing the wdt in NOWAYOUT-mode does not stop it */    return 0;}static int serial_states_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos){    if (!buf || count < 1)        return 0;    if (count > 4)        count = 4;    serial_states = 1;    if (copy_to_user(buf, (void*)&serial_states, count)) {        printk(KERN_ERR"serial_states copy_to_user failed.");        return -EFAULT;    }    return count;}static int serial_states_write(struct file *filp, const char __user *buf, size_t count, loff_t *f_pos){    serial_states = 0;    return count;}static const struct file_operations serial_states_fops = {    .owner = THIS_MODULE,    .open = serial_states_open,    .release = serial_states_release,    .read = serial_states_read,    .write = serial_states_write,};static struct miscdevice serial_states_device = {    .minor = MISC_DYNAMIC_MINOR,    .name = "serial_states",    .fops = &serial_states_fops,};static int __init u9500_init(void){    int ret = -1;    /*注册misc设备*/    ret = misc_register(&serial_states_device);    if (ret != 0) {        printk(KERN_ERR "register serial_states_device miscdevice error");        goto err1;    }    /*判断该gpio是否有效*/    ret = gpio_is_valid(SERIAL_STATES_GPIO);    if (0 == ret) {        printk(KERN_ERR "serial states gpio is invalid!\n");        goto err2;    }     /*请求gpio:其他地方就不能用了*/    ret = gpio_request(SERIAL_STATES_GPIO, "serial_states_gpio");    if (0 != ret)        goto err2;    /*设置gpio方向，以及设置输出值*/    ret = gpio_direction_output(SERIAL_STATES_GPIO, 0);    if (0 != ret)        goto err3;    /*设置gpio输出值*/    gpio_set_value(SERIAL_STATES_GPIO, 0);    printk("serial states module probe sucsecc!\n");    return 0;err3:    gpio_free(SERIAL_STATES_GPIO);err2:    misc_deregister(&serial_states_device);err1:    return ret;}module_init(u9500_init);static void __exit u9500_exit(void){    int ret = -1;    ret = gpio_is_valid(SERIAL_STATES_GPIO);    if (0 == ret)        gpio_free(SERIAL_STATES_GPIO);    misc_deregister(&serial_states_device);}module_exit(u9500_exit);MODULE_AUTHOR("vector");MODULE_LICENSE("GPL v2");MODULE_DESCRIPTION("serial_states driver");

二 Makefile 实例

serialstates-objs := serial_states.oobj-m := serialstates.o PWD  := $(shell pwd)KDIR := /home/vec/mydisk1/soure/kernel/objall:    $(MAKE) -C $(KDIR) M=$(PWD) clean:    rm -rf .*.cmd *.o *.mod.c *.ko .tmp_versions modules.order Module.symvers