On Mon, 27 May 2024 20:37:52 +0200 Vasileios Amoiridis <vassilisamir@xxxxxxxxx> wrote: > A read operation is happening as follows: > > a) Set sensor to forced mode > b) Sensor measures values and update data registers and sleeps again > c) Read data registers > > In the current implementation the read operation happens immediately > after the sensor is set to forced mode so the sensor does not have > the time to update properly the registers. This leads to the following > 2 problems: > > 1) The first ever value which is read by the register is always wrong > 2) Every read operation, puts the register into forced mode and reads > the data that were calculated in the previous conversion. > > This behaviour was tested in 2 ways: > > 1) The internal meas_status_0 register was read before and after every > read operation in order to verify that the data were ready even before > the register was set to forced mode and also to check that after the > forced mode was set the new data were not yet ready. > > 2) Physically changing the temperature and measuring the temperature > > This commit adds the waiting time in between the set of the forced mode > and the read of the data. The function is taken from the Bosch BME68x > Sensor API [1]. > > [1]: https://github.com/boschsensortec/BME68x_SensorAPI/blob/v4.4.8/bme68x.c#L490 > Fixes: 1b3bd8592780 ("iio: chemical: Add support for Bosch BME680 sensor") > Signed-off-by: Vasileios Amoiridis <vassilisamir@xxxxxxxxx> > --- > drivers/iio/chemical/bme680_core.c | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/drivers/iio/chemical/bme680_core.c b/drivers/iio/chemical/bme680_core.c > index 5db48f6d646c..dd2cd11b6dd3 100644 > --- a/drivers/iio/chemical/bme680_core.c > +++ b/drivers/iio/chemical/bme680_core.c > @@ -10,6 +10,7 @@ > */ > #include <linux/acpi.h> > #include <linux/bitfield.h> > +#include <linux/delay.h> > #include <linux/device.h> > #include <linux/module.h> > #include <linux/log2.h> > @@ -532,6 +533,26 @@ static u8 bme680_oversampling_to_reg(u8 val) > return ilog2(val) + 1; > } > > +/* > + * Taken from Bosch BME680 API: > + * https://github.com/boschsensortec/BME68x_SensorAPI/blob/v4.4.8/bme68x.c#L490 > + */ > +static int bme680_conversion_time_us(u8 meas, u8 dur) > +{ > + /* Oversampling + TPH meas + Gas meas + Forced mode + heater duration */ I'd break oversampling up /* (Oversampling ratio * time per reading) ... or something along those lines because it's related to oversampling but isn't of itself oversampling. > + return (meas * 1936) + (477 * 4) + (477 * 5) + 1000 + (dur * 1000); Trivial but I think we can rely on precedence both for correctness and readability and hence don't need the brackets > +} > + > +static void bme680_wait_for_eoc(struct bme680_data *data) Don't call it wait as that implies something is being checked. bme680_conversion_sleep() or something like that. > +{ > + int wait_eoc = bme680_conversion_time_us(data->oversampling_temp + > + data->oversampling_press + > + data->oversampling_press, > + data->heater_dur); I'd pull the calculation inline in here unless you are going to use it elsewhere in later patches. > + > + usleep_range(wait_eoc, wait_eoc + 100); > +} > + > static int bme680_chip_config(struct bme680_data *data) > { > struct device *dev = regmap_get_device(data->regmap); > @@ -622,6 +643,8 @@ static int bme680_read_temp(struct bme680_data *data, int *val) > if (ret < 0) > return ret; > > + bme680_wait_for_eoc(data); > + > ret = regmap_bulk_read(data->regmap, BME680_REG_TEMP_MSB, > &tmp, 3); > if (ret < 0) { > @@ -738,6 +761,8 @@ static int bme680_read_gas(struct bme680_data *data, > if (ret < 0) > return ret; > > + bme680_wait_for_eoc(data); > + > ret = regmap_read(data->regmap, BME680_REG_MEAS_STAT_0, &check); > if (check & BME680_GAS_MEAS_BIT) { > dev_err(dev, "gas measurement incomplete\n");
