mux의 드라이버만 가지고 있으면 아주 쉬운 문제인데요...

방법이야 많지만 우선 2가지만 보자면

1.각 채널별로 명령어를 분리 한다.

위의 I2C_RDWR 대신에 I2C_RDWR_CH1 이런식으로 나누고 해당 명령어에서 함수 호출

2.RW명령어의 인자값에 채널 ID를 준다

rdwr = ch1

if ((ret = ioctl (dev, I2C_RDWR, &rdwr)) < 0) {

머 결론은 ioctl 사용법만 아시면 쉬운 문제이구요...

mux driver안에 i2c 드라이버가 있을거니 해당 함수의 write / read 함수내에서

원하시는 기능을 구현 하시면 되겠습니다.

http://www.ipb-halle.de/~ronald/ADM5120/i2c/i2cdetect.c

파일을 참고하시기 바랍니다.

내용은 다음과 같습니다.......대충 이걸루 pca9546을 테스트 하는 듯 합니다.

/*
    i2cdetect.c - Part of i2cdetect, a user-space program to scan for I2C 
                  devices.
    Copyright (c) 1999-2001  Frodo Looijaard <[email protected]> and
                             Mark D. Studebaker <[email protected]>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

#include <errno.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <linux/i2c-dev.h>

void help(void)
{
  FILE *fptr;
  char s[100];

  fprintf(stderr,"Syntax: i2cdetect I2CBUS\n");
  fprintf(stderr,"  I2CBUS is an integer\n");
  if((fptr = fopen("/proc/bus/i2c", "r"))) {
    fprintf(stderr,"  Installed I2C busses:\n");
    while(fgets(s, 100, fptr))
      fprintf(stderr, "    %s", s);	
    fclose(fptr);
  }
}

int main(int argc, char *argv[])
{
  char *end;
  int i,j,res,i2cbus,file;
  int e1, e2, e3;
  char filename1[20];
  char filename2[20];
  char filename3[20];
  char *filename;
  long funcs;
  

  if (argc < 2) {
    fprintf(stderr,"Error: No i2c-bus specified!\n");
    help();
    exit(1);
  }

  i2cbus = strtol(argv[1],&end,0);
  if (*end) {
    fprintf(stderr,"Error: First argument not a number!\n");
    help();
    exit(1);
  }
  if ((i2cbus < 0) || (i2cbus > 0xff)) {
    fprintf(stderr,"Error: I2CBUS argument out of range!\n");
    help();
  }

/*
 * Try all three variants and give the correct error message
 * upon failure
 */

  sprintf(filename1,"/dev/i2c-%d",i2cbus);
  sprintf(filename2,"/dev/i2c%d",i2cbus);
  sprintf(filename3,"/dev/i2c/%d",i2cbus);
  if ((file = open(filename1,O_RDWR)) < 0) {
    e1 = errno;
    if ((file = open(filename2,O_RDWR)) < 0) {
      e2 = errno;
      if ((file = open(filename3,O_RDWR)) < 0) {
        e3 = errno;
        if(e1 == ENOENT && e2 == ENOENT && e3 == ENOENT) {
          fprintf(stderr,"Error: Could not open file `%s', `%s', or `%s': %s\n",
                     filename1,filename2,filename3,strerror(ENOENT));
        }
        if (e1 != ENOENT) {
          fprintf(stderr,"Error: Could not open file `%s' : %s\n",
                     filename1,strerror(e1));
          if(e1 == EACCES)
            fprintf(stderr,"Run as root?\n");
        }
        if (e2 != ENOENT) {
          fprintf(stderr,"Error: Could not open file `%s' : %s\n",
                     filename2,strerror(e2));
          if(e2 == EACCES)
            fprintf(stderr,"Run as root?\n");
        }
        if (e3 != ENOENT) {
          fprintf(stderr,"Error: Could not open file `%s' : %s\n",
                     filename3,strerror(e3));
          if(e3 == EACCES)
            fprintf(stderr,"Run as root?\n");
        }
        exit(1);
      } else {
         filename = filename3;
      }
    } else {
       filename = filename2;
    }
  } else {
    filename = filename1;
  }

  if (ioctl(file,I2C_FUNCS,&funcs) < 0) {
    fprintf(stderr,
            "Error: Could not get the adapter functionality maxtrix: %s\n",
            strerror(errno));
    exit(1);
  }
  if (! (funcs & I2C_FUNC_SMBUS_QUICK)) {
    fprintf(stderr,
            "Error: Can't use SMBus Quick Write command "
            "on this bus (ISA bus?)\n");
    exit(1);
  }
  
  fprintf(stderr,"  WARNING! This program can confuse your I2C bus, "
          "cause data loss and worse!\n");
  fprintf(stderr,"  I will probe file %s\n", filename);
  fprintf(stderr,"  You have five seconds to reconsider and press CTRL-C!\n\n");
  sleep(5);

  printf("     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f\n");
  for (i = 0; i < 128; i+=16) {
    printf("%02x: ",i);
    for(j = 0; j < 16; j++) {
      if (ioctl(file,I2C_SLAVE,i+j) < 0) {
        if (errno == EBUSY) {
          printf("UU ");
          continue;
        } else {
          fprintf(stderr,"Error: Could not set address to %02x: %s\n",i+j,
                  strerror(errno));
          exit(1);
        }
      }

      res = i2c_smbus_write_quick(file, I2C_SMBUS_WRITE);
      if (res < 0)
        printf("XX ");
      else
        printf("%02x ",i+j);
    }
    printf("\n");
  }
  exit(0);
}