[PATCH 2/5] iio: imu: inv_mpu6050: switch to use sample rate divider

[Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>]

Instead of storing fifo rate in Hz, store the chip internal sample
rate divider. This will be more useful for timestamping. There
are both equivalent.

Signed-off-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
---
 drivers/iio/imu/inv_mpu6050/inv_mpu_core.c | 15 +++++++++------
 drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h  |  4 ++--
 2 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c b/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c
index 1e7e750..9e5c5e7 100644
--- a/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c
+++ b/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c
@@ -82,7 +82,7 @@ static const struct inv_mpu6050_reg_map reg_set_6050 = {
 static const struct inv_mpu6050_chip_config chip_config_6050 = {
 	.fsr = INV_MPU6050_FSR_2000DPS,
 	.lpf = INV_MPU6050_FILTER_20HZ,
-	.fifo_rate = INV_MPU6050_INIT_FIFO_RATE,
+	.divider = (INV_MPU6050_ONE_K_HZ / INV_MPU6050_INIT_FIFO_RATE) - 1,
 	.gyro_fifo_enable = false,
 	.accl_fifo_enable = false,
 	.accl_fs = INV_MPU6050_FS_02G,
@@ -628,7 +628,7 @@ static ssize_t
 inv_mpu6050_fifo_rate_store(struct device *dev, struct device_attribute *attr,
 			    const char *buf, size_t count)
 {
-	s32 fifo_rate;
+	int fifo_rate;
 	u8 d;
 	int result;
 	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
@@ -644,8 +644,12 @@ inv_mpu6050_fifo_rate_store(struct device *dev, struct device_attribute *attr,
 	if (result)
 		return result;
 
+	/* compute freq divider and update fifo rate in case of truncation */
+	d = INV_MPU6050_ONE_K_HZ / fifo_rate - 1;
+	fifo_rate = INV_MPU6050_ONE_K_HZ / (d + 1);
+
 	mutex_lock(&st->lock);
-	if (fifo_rate == st->chip_config.fifo_rate) {
+	if (d == st->chip_config.divider) {
 		result = 0;
 		goto fifo_rate_fail_unlock;
 	}
@@ -653,11 +657,10 @@ inv_mpu6050_fifo_rate_store(struct device *dev, struct device_attribute *attr,
 	if (result)
 		goto fifo_rate_fail_unlock;
 
-	d = INV_MPU6050_ONE_K_HZ / fifo_rate - 1;
 	result = regmap_write(st->map, st->reg->sample_rate_div, d);
 	if (result)
 		goto fifo_rate_fail_power_off;
-	st->chip_config.fifo_rate = fifo_rate;
+	st->chip_config.divider = d;
 
 	result = inv_mpu6050_set_lpf(st, fifo_rate);
 	if (result)
@@ -685,7 +688,7 @@ inv_fifo_rate_show(struct device *dev, struct device_attribute *attr,
 	unsigned fifo_rate;
 
 	mutex_lock(&st->lock);
-	fifo_rate = st->chip_config.fifo_rate;
+	fifo_rate = INV_MPU6050_ONE_K_HZ / (st->chip_config.divider + 1);
 	mutex_unlock(&st->lock);
 
 	return scnprintf(buf, PAGE_SIZE, "%u\n", fifo_rate);
diff --git a/drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h b/drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h
index a92ddd4..8d9044c 100644
--- a/drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h
+++ b/drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h
@@ -86,7 +86,7 @@ enum inv_devices {
  *  @accl_fs:		accel full scale range.
  *  @accl_fifo_enable:	enable accel data output
  *  @gyro_fifo_enable:	enable gyro data output
- *  @fifo_rate:		FIFO update rate.
+ *  @divider:		sample rate divider.
  */
 struct inv_mpu6050_chip_config {
 	unsigned int fsr:2;
@@ -94,7 +94,7 @@ struct inv_mpu6050_chip_config {
 	unsigned int accl_fs:2;
 	unsigned int accl_fifo_enable:1;
 	unsigned int gyro_fifo_enable:1;
-	u16 fifo_rate;
+	u8 divider;
 	u8 user_ctrl;
 };
 
-- 
2.7.4