iio: inv_mpu6050: Check WHO_AM_I register on probe

This can be used to distinguish mpu6500. This is a warning rather than
an error because the differences are mostly irrelevant and it's nice to
avoid breaking users with slightly incorrect ACPI/DT.
Signed-off-by: Crestez Dan Leonard <leonard.crestez@intel.com>
Acked-by: Ge Gao <ggao@invensense.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/imu/inv_mpu6050/inv_mpu_core.c

@@ -91,16 +91,19 @@ static const struct inv_mpu6050_chip_config chip_config_6050 = {
 /* Indexed by enum inv_devices */
 static const struct inv_mpu6050_hw hw_info[] = {
 	{
+		.whoami = INV_MPU6050_WHOAMI_VALUE,
 		.name = "MPU6050",
 		.reg = &reg_set_6050,
 		.config = &chip_config_6050,
 	},
 	{
+		.whoami = INV_MPU6500_WHOAMI_VALUE,
 		.name = "MPU6500",
 		.reg = &reg_set_6500,
 		.config = &chip_config_6050,
 	},
 	{
+		.whoami = INV_MPU6000_WHOAMI_VALUE,
 		.name = "MPU6000",
 		.reg = &reg_set_6050,
 		.config = &chip_config_6050,
@@ -749,6 +752,7 @@ static const struct iio_info mpu_info = {
 static int inv_check_and_setup_chip(struct inv_mpu6050_state *st)
 {
 	int result;
+	unsigned int regval;
 
 	st->hw  = &hw_info[st->chip_type];
 	st->reg = hw_info[st->chip_type].reg;
@@ -759,6 +763,17 @@ static int inv_check_and_setup_chip(struct inv_mpu6050_state *st)
 	if (result)
 		return result;
 	msleep(INV_MPU6050_POWER_UP_TIME);
+
+	/* check chip self-identification */
+	result = regmap_read(st->map, INV_MPU6050_REG_WHOAMI, &regval);
+	if (result)
+		return result;
+	if (regval != st->hw->whoami) {
+		dev_warn(regmap_get_device(st->map),
+				"whoami mismatch got %#02x expected %#02hhx for %s\n",
+				regval, st->hw->whoami, st->hw->name);
+	}
+
 	/*
 	 * toggle power state. After reset, the sleep bit could be on
 	 * or off depending on the OTP settings. Toggling power would

drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h

@@ -93,11 +93,13 @@ struct inv_mpu6050_chip_config {
 
 /**
  *  struct inv_mpu6050_hw - Other important hardware information.
+ *  @whoami:	Self identification byte from WHO_AM_I register
  *  @name:      name of the chip.
  *  @reg:   register map of the chip.
  *  @config:    configuration of the chip.
  */
 struct inv_mpu6050_hw {
+	u8 whoami;
 	u8 *name;
 	const struct inv_mpu6050_reg_map *reg;
 	const struct inv_mpu6050_chip_config *config;
@@ -215,6 +217,12 @@ struct inv_mpu6050_state {
 #define INV_MPU6050_MIN_FIFO_RATE            4
 #define INV_MPU6050_ONE_K_HZ                 1000
 
+#define INV_MPU6050_REG_WHOAMI			117
+
+#define INV_MPU6000_WHOAMI_VALUE		0x68
+#define INV_MPU6050_WHOAMI_VALUE		0x68
+#define INV_MPU6500_WHOAMI_VALUE		0x70
+
 /* scan element definition */
 enum inv_mpu6050_scan {
 	INV_MPU6050_SCAN_ACCL_X,