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iio: st_lsm6dsx: Fixed calibrated timestamp calculation

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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: cb3b6b8e1b ("iio: imu: st_lsm6dsx: add odr calibration feature")
Signed-off-by: Mario Tesi <mario.tesi@st.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
This commit is contained in:
Mario Tesi
2025-10-15 18:16:19 +02:00
committed by Jonathan Cameron
parent cb372b4f46
commit 8abbf45fcd
2 changed files with 26 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files

18
drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
View File

@@ -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;
};
/**

19
drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
View File

@@ -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;