S3C2440 gpio 제어 (소스 문제점 지적 부탁드립니다.)

안녕하세요.

gpio제어 학습을 해보려고 여기저기 참고해서 소스를 작성했습니다만, 역시 실력이 개발이라 오류가 발생하네요.

전체 소스입니다. 제가 무엇을 잘못했는지.. 조언 부탁드립니다.

아래는 s3c2440a 메뉴얼에서 발췌한 GPF 레지스터 정보입니다.

PORT F CONTROL REGISTERS (GPFCON, GPFDAT)
If GPF0–GPF7 will be used for wake-up signals at power down mode, the ports will be set in interrupt mode.
Register        Address            R/W       Description                                       Reset Value
GPFCON     0x56000050     R/W       Configures the pins of port F           0x0
GPFDAT     0x56000054     R/W       The data register for port F               Undef.
GPFUP         0x56000058    R/W       Pull-up disable register for port F     0x000
Reserved       0x5600005c     –            –                                                         –

 gpio_dev.c 디바이스 파일입니다.

#include <linux/module.h> // 모듈에 관한 정의
#include <linux/init.h>  // init_module()과 cleanup_module()
#include <linux/fs.h>   // file_operations 구조체
#include <asm/uaccess.h> // copy_to_user()
#include <asm/io.h>    // GPIO controller에 관한 정의

#define DEV_NAME "gpio"
#define DEV_MAJOR 250

#define rGPFCON (*(volatile unsigned *)0x56000050)
#define rGPFDAT (*(volatile unsigned *)0x56000054)
#define rGPFUP  (*(volatile unsigned *)0x56000058)

int gpio_open(struct inode *inode, struct file *filp)
{
 printk("gpio driver open\n");
 
 return 0;
}

ssize_t gpio_write(struct file *filp, void *buf, size_t count, loff_t *f_pos)
{
  unsigned int buffer;
 
 copy_from_user(buffer,(int *)buf, sizeof(buffer));

 rGPFCON = (rGPFCON &~(0x3<<14))|(0x1<<14);     // GPF 7번 핀을 출력으로 설정
 rGPFUP  = rGPFUP|(0x1<<7);             // 출력으로 사용하기 위해 GPF 7번 핀의 풀업제거
 rGPFDAT = (rGPFDAT &~(0x1<<7))|((buffer & 0x1)<<7); // GPF 7번핀에 데이터 쓰기
 
 return 0;
}

int gpio_release(struct inode *inode, struct file *filp)
{
 printk("gpio driver close\n");

 return 0;
}

struct file_operations gpio_fops =
{
 .owner    = THIS_MODULE,
  .write  = gpio_write,
 .open   = gpio_open,
 .release = gpio_release,
};

int gpio_init(void)
{
 int result;
 
 printk("call gpio_init\n");
 
 result = register_chrdev(DEV_MAJOR, DEV_NAME, &gpio_fops);
 if(result < 0) return result;
  
 return 0;
}

int gpio_exit(void)
{
 printk("call gpio_exit\n");
 
 unregister_chrdev(DEV_MAJOR, DEV_NAME);
}

module_init(gpio_init);
module_exit(gpio_exit);

MODULE_LICENSE("Dual BSD/GPL");

gpio_app.c 응용프로그램 파일입니다..

#include <stdio.h>
#include <fcntl.h> // open()의 flag 정의
#include <errno.h> // error 값 정의

int main(void)
{
 int fd, buf;
 
 printf("device file open\n");
 
 fd=open("/dev/gpio", O_RDWR|O_NDELAY);
 if(fd<0) {
  perror("/dev/gpio open error");
  exit(1);
 }
  
 for(buf=0;buf<10;buf++) {
  write(fd, buf, sizeof(buf));
  sleep(1);
 }

 close(fd);
 return 0;
}

make 메시지 입니다.

[hdd@hdd-server nfs]$ make
make -C /opt/linux-2.6.21 SUBDIRS=/home/nfs modules
make[1]: Entering directory `/opt/linux-2.6.21'
  CC [M]  /home/nfs/gpio_dev.o
/home/nfs/gpio_dev.c: In function `gpio_write':
/home/nfs/gpio_dev.c:25: warning: passing arg 1 of `copy_from_user' makes pointer from integer without a cast
/home/nfs/gpio_dev.c: At top level:
/home/nfs/gpio_dev.c:44: warning: initialization from incompatible pointer type
/home/nfs/gpio_dev.c: In function `__exittest':
/home/nfs/gpio_dev.c:69: warning: return from incompatible pointer type
/home/nfs/gpio_dev.c: In function `gpio_write':
/home/nfs/gpio_dev.c:23: warning: 'buffer' might be used uninitialized in this function
/home/nfs/gpio_dev.c: In function `gpio_exit':
/home/nfs/gpio_dev.c:66: warning: control reaches end of non-void function
  Building modules, stage 2.
  MODPOST 1 modules
  CC      /home/nfs/gpio_dev.mod.o
  LD [M]  /home/nfs/gpio_dev.ko
make[1]: Leaving directory `/opt/linux-2.6.21'
arm-linux-gcc -o gpio_app gpio_app.c

타켓 시스템으로 옮겨와서 실행

[root@falinux nfs]$ insmod gpio_dev.ko

[root@falinux nfs]$ mknod /dev/gpio c 250 0

[root@falinux nfs]$ lsmod
Module                  Size  Used by    Not tainted
gpio_dev                1888  0

[root@falinux nfs]$ ./gpio_app
device file open
Segmentation fault

커널 메시지를 살펴보니...

[root@falinux nfs]$ dmesg

...

call gpio_init
gpio driver open
Unable to handle kernel NULL pointer dereference at virtual address 00000004
pgd = c0df0000
[00000004] *pgd=30dee031, *pte=00000000, *ppte=00000000
Internal error: Oops: 817 [#1]
Modules linked in: gpio_dev
CPU: 0
PC is at __memzero+0x60/0x80
LR is at __lock_text_end+0x638/0x8f0
pc : [<c014aa60>]    lr : [<c02c8718>]    Not tainted
sp : c0d95f38  ip : 0000001c  fp : c0d95f54
r10: 40135f6c  r9 : c0d94000  r8 : 00000000
r7 : c0d95f78  r6 : 00000000  r5 : c05b5520  r4 : 00000004
r3 : 00000000  r2 : 00000000  r1 : 00000004  r0 : 00000004
Flags: nzcv  IRQs on  FIQs on  Mode SVC_32  Segment user
Control: C000717F
Table: 30DF0000  DAC: 00000015
Process gpio_app (pid: 978, stack limit = 0xc0d94250)
Stack: (0xc0d95f38 to 0xc0d96000)
5f20:                                                       00000004 00000004
5f40: bf00005c 00000004 c0d95f74 c0d95f58 c0086450 bf000030 c05b5540 c05b5520
5f60: c0d95f78 00000000 c0d95fa4 c0d95f78 c0086544 c00863a0 00000000 00000000
5f80: 00000000 4001c3bc bed93c84 00008694 00000004 c0028dc4 00000000 c0d95fa8
5fa0: c0028c20 c0086508 4001c3bc bed93c84 00000003 00000000 00000004 00000000
5fc0: 4001c3bc bed93c84 00008694 00000001 401397fc 000085e8 40135f6c bed93c54
5fe0: 00000000 bed93c3c 00003d10 400df400 60000010 00000003 00000000 00000000
Backtrace:
[<bf000020>] (gpio_write+0x0/0x9c [gpio_dev]) from [<c0086450>] (vfs_write+0xc0/0xf4)
 r4 = 00000004
[<c0086390>] (vfs_write+0x0/0xf4) from [<c0086544>] (sys_write+0x4c/0x74)
 r7 = 00000000  r6 = C0D95F78  r5 = C05B5520  r4 = C05B5540
[<c00864f8>] (sys_write+0x0/0x74) from [<c0028c20>] (ret_fast_syscall+0x0/0x2c)
 r8 = C0028DC4  r7 = 00000004  r6 = 00008694  r5 = BED93C84
 r4 = 4001C3BC
Code: e49de004 e3110008 18a0000c e3110004 (14802004)
gpio driver close