下面代码描述了在用户层访问smi／mdio总线， 读写phy芯片寄存器的通用代码。Linux内核2.6以上通用。

将下面代码编译后，将可执行文件a.out 重命名为mdio

mdio eth0 1          读取phy寄存器1的数值
mdio eth0 0 0x1120      将0x1120写入 phy寄存器1

eth0 为mac层控制器的名称， 一般为eth0 或mgmt0。
 

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <linux/mii.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <linux/sockios.h>
#include <linux/types.h>
#include <netinet/in.h>
 
 
#define reteck(ret)     \
        if(ret < 0){    \
            printf("%m! \"%s\" : line: %d\n", __func__, __LINE__);   \
            goto lab;   \
        }
 
#define help() \
    printf("mdio:\n");                  \
    printf("read operation: mdio reg_addr\n");          \
    printf("write operation: mdio reg_addr value\n");    \
    printf("For example:\n");            \
    printf("mdio eth0 1\n");             \
    printf("mdio eth0 0 0x12\n\n");      \
    exit(0);
 
int sockfd;
 
int main(int argc, char *argv[]){
        
    if(argc == 1 || !strcmp(argv[1], "-h")){
        help();
    }
    
    struct mii_ioctl_data *mii = NULL;
    struct ifreq ifr;
    int ret;
 
    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, argv[1], IFNAMSIZ - 1);
 
    sockfd = socket(PF_LOCAL, SOCK_DGRAM, 0);
    reteck(sockfd);
 
    //get phy address in smi bus
    ret = ioctl(sockfd, SIOCGMIIPHY, &ifr);
    reteck(ret);
 
    mii = (struct mii_ioctl_data*)&ifr.ifr_data;
 
    if(argc == 3){
 
        mii->reg_num    = (uint16_t)strtoul(argv[2], NULL, 0);
        
        ret = ioctl(sockfd, SIOCGMIIREG, &ifr);
        reteck(ret);
    
        printf("read phy addr: 0x%x  reg: 0x%x   value : 0x%x\n\n", mii->phy_id, mii->reg_num, mii->val_out);
	}else if(argc == 4){
 
        mii->reg_num    = (uint16_t)strtoul(argv[2], NULL, 0);
        mii->val_in     = (uint16_t)strtoul(argv[3], NULL, 0);
 
        ret = ioctl(sockfd, SIOCSMIIREG, &ifr);
        reteck(ret);
 
        printf("write phy addr: 0x%x  reg: 0x%x  value : 0x%x\n\n", mii->phy_id, mii->reg_num, mii->val_in);
    }
 
lab:
    close(sockfd);
    return 0;
}