[PATCH 3/3] iio: imu: Enable checking of presence of device

[Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>]

Added logic to check presence of MPU6050 before continuing. Currently
only i2c writes are used in the initialzation path, which don't return
any error, if some i2c device responds. In this case it continues to
create iio devices, which don't work.
This can be reproduced in a PC like platform, where ACPI definition
of this defines multiple i2c addresses. We need to check for an valid
i2c address by checking some signature before continuing.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
---
 drivers/iio/imu/inv_mpu6050/inv_mpu_core.c | 15 ++++++++++++++-
 drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h  |  4 ++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c b/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c
index 6ba565a..e062acd 100644
--- a/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c
+++ b/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c
@@ -62,6 +62,7 @@ static const struct inv_mpu6050_reg_map reg_set_6050 = {
 	.pwr_mgmt_1             = INV_MPU6050_REG_PWR_MGMT_1,
 	.pwr_mgmt_2             = INV_MPU6050_REG_PWR_MGMT_2,
 	.int_pin_cfg		= INV_MPU6050_REG_INT_PIN_CFG,
+	.who_am_i		= INV_MPU6050_REG_WHOAMI,
 };
 
 static const struct inv_mpu6050_chip_config chip_config_6050 = {
@@ -617,7 +618,7 @@ static const struct iio_info mpu_info = {
 	.validate_trigger = inv_mpu6050_validate_trigger,
 };
 
-int inv_set_bypass_status(struct inv_mpu6050_state *st, bool enable)
+static int inv_set_bypass_status(struct inv_mpu6050_state *st, bool enable)
 {
 	int ret;
 
@@ -650,6 +651,18 @@ static int inv_check_and_setup_chip(struct inv_mpu6050_state *st,
 	if (result)
 		return result;
 	msleep(INV_MPU6050_POWER_UP_TIME);
+
+	result = i2c_smbus_read_byte_data(st->client, st->reg->who_am_i);
+	if (result < 0) {
+		dev_err(&st->client->dev, "Error reading WhoAmI\n");
+		return result;
+	}
+	if (result != INV_MPU6500_UNIQUE_ID) {
+		dev_err(&st->client->dev, "Not a valid MPU6500 device %x\n",
+								result);
+		return -ENOSYS;
+	}
+
 	/* toggle power state. After reset, the sleep bit could be on
 		or off depending on the OTP settings. Toggling power would
 		make it in a definite state as well as making the hardware
diff --git a/drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h b/drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h
index de5aa22..87649bd 100644
--- a/drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h
+++ b/drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h
@@ -55,6 +55,7 @@ struct inv_mpu6050_reg_map {
 	u8 pwr_mgmt_1;
 	u8 pwr_mgmt_2;
 	u8 int_pin_cfg;
+	u8 who_am_i;
 };
 
 /*device enum */
@@ -189,6 +190,9 @@ struct inv_mpu6050_state {
 #define INV_MPU6050_REG_INT_PIN_CFG		0x37
 #define INV_MPU6050_BIT_BYPASS_EN		0x2
 
+#define INV_MPU6050_REG_WHOAMI			0x75
+#define INV_MPU6500_UNIQUE_ID			0x70
+
 /* scan element definition */
 enum inv_mpu6050_scan {
 	INV_MPU6050_SCAN_ACCL_X,
-- 
1.7.11.7