mpu6050: Add check of WHO_AM_I register value

Most of i2c chips have a special read-only register with unique id.
So the easiest way to communicate with the device is to read that register.
It should be accessibe even during power off modes and so failing to read it
means no communication with the device. Reading non-expected value will indicate
wrong adress or data size used, or incorrect device connected (other revision).

Reading small amounts of data is easiest done using i2c_smbus_read_byte()
or similar functions. Why smbus? Because they are wrappers to i2c_transfer()
function and have internal device address as a parameter. This eliminates need
to fill i2c_transfer structure for each small read or write.
Using i2c_transfer() should be considered for large blocks of data and gives
a performance boost over i2c_smbus wrappers.

Signed-off-by: Andriy.Khulap <[email protected]>

mpu6050/mpu6050-regs.h

@@ -0,0 +1,33 @@
+#ifndef _MPU6050_REGS_H
+#define _MPU6050_REGS_H
+
+/* Registed addresses */
+#define REG_CONFIG			0x1A
+#define REG_GYRO_CONFIG		0x1B
+#define REG_ACCEL_CONFIG	0x1C
+#define REG_FIFO_EN			0x23
+#define REG_INT_PIN_CFG		0x37
+#define REG_INT_ENABLE		0x38
+#define REG_ACCEL_XOUT_H	0x3B
+#define REG_ACCEL_XOUT_L	0x3C
+#define REG_ACCEL_YOUT_H	0x3D
+#define REG_ACCEL_YOUT_L	0x3E
+#define REG_ACCEL_ZOUT_H	0x3F
+#define REG_ACCEL_ZOUT_L	0x40
+#define REG_TEMP_OUT_H		0x41
+#define REG_TEMP_OUT_L		0x42
+#define REG_GYRO_XOUT_H		0x43
+#define REG_GYRO_XOUT_L		0x44
+#define REG_GYRO_YOUT_H		0x45
+#define REG_GYRO_YOUT_L		0x46
+#define REG_GYRO_ZOUT_H		0x47
+#define REG_GYRO_ZOUT_L		0x48
+#define REG_USER_CTRL		0x6A
+#define REG_PWR_MGMT_1		0x6B
+#define REG_PWR_MGMT_2		0x6C
+#define REG_WHO_AM_I		0x75
+
+/* Register values */
+#define MPU6050_WHO_AM_I	0x68
+
+#endif /* _MPU6050_REGS_H */

mpu6050/mpu6050.c

@@ -5,11 +5,34 @@
 #include <linux/i2c.h>
 #include <linux/i2c-dev.h>
 
+#include "mpu6050-regs.h"
+
 static int mpu6050_probe(struct i2c_client *drv_client,
 			 const struct i2c_device_id *id)
 {
+	int ret;
+
 	dev_info(&drv_client->dev,
 		"i2c client address is 0x%X\n", drv_client->addr);
+
+	/* Read who_am_i register */
+	ret = i2c_smbus_read_byte_data(drv_client, REG_WHO_AM_I);
+	if (IS_ERR_VALUE(ret)) {
+		dev_err(&drv_client->dev,
+			"i2c_smbus_read_byte_data() failed with error: %d\n",
+			ret);
+		return ret;
+	}
+	if (ret != MPU6050_WHO_AM_I) {
+		dev_err(&drv_client->dev,
+			"wrong i2c device found: expected 0x%X, found 0x%X\n",
+			MPU6050_WHO_AM_I, ret);
+		return -1;
+	}
+	dev_info(&drv_client->dev,
+		"i2c mpu6050 device found, WHO_AM_I register value = 0x%X\n",
+		ret);
+
 	dev_info(&drv_client->dev, "i2c driver probed\n");
 	return 0;
 }