Commit 8abbf45f authored by Mario Tesi's avatar Mario Tesi Committed by Jonathan Cameron
Browse files

iio: st_lsm6dsx: Fixed calibrated timestamp calculation 



The calibrated timestamp is calculated from the nominal value using the
formula:
  ts_gain[ns] ≈ ts_sensitivity - (ts_trim_coeff * val) / 1000.

The values of ts_sensitivity and ts_trim_coeff are not the same for all
devices, so it is necessary to differentiate them based on the part name.
For the correct values please consult the relevant AN.

Fixes: cb3b6b8e ("iio: imu: st_lsm6dsx: add odr calibration feature")
Signed-off-by: default avatarMario Tesi <mario.tesi@st.com>
Acked-by: default avatarLorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: default avatarJonathan Cameron <Jonathan.Cameron@huawei.com>
parent cb372b4f

drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h

+18 −0
Original line number Diff line number Diff line
@@ -192,6 +192,22 @@ struct st_lsm6dsx_fifo_ops { 
 * @fifo_en: Hw timer FIFO enable register info (addr + mask).

 * @decimator: Hw timer FIFO decimator register info (addr + mask).

 * @freq_fine: Difference in % of ODR with respect to the typical.

 * @ts_sensitivity: Nominal timestamp sensitivity.

 * @ts_trim_coeff: Coefficient for calculating the calibrated timestamp gain.

 *                 This coefficient comes into play when linearizing the formula

 *                 used to calculate the calibrated timestamp (please see the

 *                 relevant formula in the AN for the specific IMU).

 *                 For example, in the case of LSM6DSO we have:

 *

 *                  1 / (1 + x) ~= 1 - x (Taylor’s Series)

 *                  ttrim[s] = 1 / (40000 * (1 + 0.0015 * val)) (from AN5192)

 *                  ttrim[ns] ~= 25000 - 37.5 * val

 *                  ttrim[ns] ~= 25000 - (37500 * val) / 1000

 *

 *                  so, replacing ts_sensitivity = 25000 and

 *                  ts_trim_coeff = 37500

 *

 *                  ttrim[ns] ~= ts_sensitivity - (ts_trim_coeff * val) / 1000

 */

struct st_lsm6dsx_hw_ts_settings {

	struct st_lsm6dsx_reg timer_en;
@@ -199,6 +215,8 @@ struct st_lsm6dsx_hw_ts_settings { 
	struct st_lsm6dsx_reg fifo_en;

	struct st_lsm6dsx_reg decimator;

	u8 freq_fine;

	u16 ts_sensitivity;

	u16 ts_trim_coeff;

};



/**

drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c

+8 −11
Original line number Diff line number Diff line
@@ -94,8 +94,6 @@ 


#define ST_LSM6DSX_REG_WHOAMI_ADDR		0x0f



#define ST_LSM6DSX_TS_SENSITIVITY		25000UL /* 25us */



static const struct iio_chan_spec st_lsm6dsx_acc_channels[] = {

	ST_LSM6DSX_CHANNEL_ACC(IIO_ACCEL, 0x28, IIO_MOD_X, 0),

	ST_LSM6DSX_CHANNEL_ACC(IIO_ACCEL, 0x2a, IIO_MOD_Y, 1),
@@ -983,6 +981,8 @@ static const struct st_lsm6dsx_settings st_lsm6dsx_sensor_settings[] = { 
				.mask = GENMASK(7, 6),

			},

			.freq_fine = 0x63,

			.ts_sensitivity = 25000,

			.ts_trim_coeff = 37500,

		},

		.shub_settings = {

			.page_mux = {
@@ -1196,6 +1196,8 @@ static const struct st_lsm6dsx_settings st_lsm6dsx_sensor_settings[] = { 
				.mask = GENMASK(7, 6),

			},

			.freq_fine = 0x63,

			.ts_sensitivity = 25000,

			.ts_trim_coeff = 37500,

		},

		.event_settings = {

			.enable_reg = {
@@ -1371,6 +1373,8 @@ static const struct st_lsm6dsx_settings st_lsm6dsx_sensor_settings[] = { 
				.mask = GENMASK(7, 6),

			},

			.freq_fine = 0x4f,

			.ts_sensitivity = 21701,

			.ts_trim_coeff = 28212,

		},

		.shub_settings = {

			.page_mux = {
@@ -2248,20 +2252,13 @@ static int st_lsm6dsx_init_hw_timer(struct st_lsm6dsx_hw *hw) 
	}



	/* calibrate timestamp sensitivity */

	hw->ts_gain = ST_LSM6DSX_TS_SENSITIVITY;

	hw->ts_gain = ts_settings->ts_sensitivity;

	if (ts_settings->freq_fine) {

		err = regmap_read(hw->regmap, ts_settings->freq_fine, &val);

		if (err < 0)

			return err;



		/*

		 * linearize the AN5192 formula:

		 * 1 / (1 + x) ~= 1 - x (Taylor’s Series)

		 * ttrim[s] = 1 / (40000 * (1 + 0.0015 * val))

		 * ttrim[ns] ~= 25000 - 37.5 * val

		 * ttrim[ns] ~= 25000 - (37500 * val) / 1000

		 */

		hw->ts_gain -= ((s8)val * 37500) / 1000;

		hw->ts_gain -= ((s8)val * ts_settings->ts_trim_coeff) / 1000;

	}



	return 0;