On stout I2C interface is supported as device driver in Yocto.

/dev/i2c-0
/dev/i2c-1
/dev/i2c-2
/dev/i2c-7

Example program (part of retest)

i2c.h

/*
 * i2c.h
 *
 *  Created on: Jan 3, 2016
 *      Author: rcar
 */
 
#ifndef I2C_H_
#define I2C_H_
 
#include <stdint.h>
 
void i2cOpen(uint8_t devno);
void i2cClose();
void i2cSetAddress(uint8_t address);
uint8_t i2cReadData8(uint8_t reg);
int16_t i2cReadData16(uint8_t reg);
void i2cWriteData8(uint8_t reg, uint8_t value);
void i2cWriteData16(uint8_t reg, uint16_t value);
void i2cDetectDevice(void);
void i2cReadRCValues(void);
 
#endif /* I2C_H_ */

i2c.c

/*
 * i2c.c
 *
 *  Created on: Jan 3, 2016
 *      Author: rcar
 */
 
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <linux/i2c-dev.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <fcntl.h>
 
#include "i2c.h"
#include "mpu.h"
 
// I2C Linux device handle
int g_i2cFile;
 
//------------------------------------------------------------------------
// open the Linux device
void i2cOpen(uint8_t devno)
{
	char device[20];
	snprintf(device, sizeof device, "/dev/i2c-%d", devno);
	g_i2cFile = open(device, O_RDWR);
	if (g_i2cFile < 0) {
		perror("i2cOpen");
		exit(1);
	}
}
 
//------------------------------------------------------------------------
// close the Linux device
void i2cClose()
{
	close(g_i2cFile);
}
 
//------------------------------------------------------------------------
// set the I2C slave address for all subsequent I2C device transfers
void i2cSetAddress(uint8_t address)
{
	if (ioctl(g_i2cFile, I2C_SLAVE, address) < 0) {
		perror("i2cSetAddress");
		exit(1);
	}
}
 
//------------------------------------------------------------------------
// read 8-bit value from register reg
uint8_t i2cReadData8(uint8_t reg) {
 
	uint8_t  data;
 
	if (write(g_i2cFile, &reg, 1) != 1) {
		perror("i2cReadData8 set register");
		return 0;
	}
	if (read(g_i2cFile, &data, 1) != 1) {
		perror("i2cReadData8 read value");
		return 0;
	}
	return data;
}
 
//------------------------------------------------------------------------
// read a 16 bit value from a register pair
// read high byte of value from register reg,
// and low byte of value from register reg+1
int16_t i2cReadData16(uint8_t reg) {
 
	uint8_t  data[2];
 
	if (write(g_i2cFile, &reg, 1) != 1) {
		perror("i2cReadData8 set register");
		return 0;
	}
	if (read(g_i2cFile, data, 2) != 2) {
		perror("i2cReadData8 read value");
		return 0;
	}
	return data[1] | (data[0] << 8);
}
 
//------------------------------------------------------------------------
// write a 8 bit value to a register reg
void i2cWriteData8(uint8_t reg, uint8_t value)
{
	uint8_t data[2];
	data[0] = reg;
	data[1] = value;
	if (write(g_i2cFile, data, 2) != 2) {
		perror("i2cWriteData8");
	}
}
 
//------------------------------------------------------------------------
// write a 16 bit value to a register pair
// write high byte of value to register reg,
// and low byte of value to register reg+1
void i2cWriteData16(uint8_t reg, uint16_t value)
{
	uint8_t data[3];
	data[0] = reg;
	data[1] = (value >> 8) & 0xff;
	data[2] = value & 0xff;
	if (write(g_i2cFile, data, 3) != 3) {
		perror("i2cWriteData16");
	}
}
 
//------------------------------------------------------------------------
// try to detect both i2c devices
// MPU-6050 has a fixed ID of 0x68 at reg 0x75
// RC-Mixer has a fixed ID of 0x34 at reg 0x1F
void i2cDetectDevice(void) {
 
	uint16_t result;
 
	// MPU-6050
	i2cOpen(2);					// is at i2c-2
	i2cSetAddress(MPU6050_ADDRESS);		// address of MPU-6050
	result = i2cReadData8(MPU6050_RA_WHO_AM_I);
	printf("Check Addr:0x68 Reg:0x75 Data:%x", result);
	if (result == 0x68) printf("  => MPU-6050 found!\n");
		else printf("  => MPU-6050 missing!\n");
	i2cClose();
 
	// RC-Mixer
	i2cOpen(1);					// is at i2c-1
	i2cSetAddress(0x34);		// address of RC-Mixer
	result = i2cReadData8(31);
	printf("check Addr:0x34 Reg:0x1F Data:%x", result);
	if (result == 0x34) printf("  => RC-Mixer found!\n");
		else printf("  => RC-Mixer missing!\n");
	i2cClose();
}
 
//------------------------------------------------------------------------
// get RC values from RC-Mixer
void i2cReadRCValues(void) {
 
	uint16_t result;
	int i;
 
	// RC-Mixer
	i2cOpen(1);					// is at i2c-1
	i2cSetAddress(0x34);		// address of RC-Mixer
 
	printf("RC value from RC-Mixer\n");
	printf("CH1   CH2   CH3   CH4   CH5   PWM3  PWM4  STEER MOTOR\n");
	for(i=0;i<9;i++) {
		result = i2cReadData16(i*2);
		printf("%04d  ",result);
	}
	printf("\n");
	i2cClose();
}