On Sun, 23 Jun 2019 14:29:10 +0200 Andreas Klinger <[email protected]> wrote:
> The measured time value in the driver is limited to the maximum distance > which can be read by the sensor. This limitation was wrong and is fixed > by this patch. > > It also takes into account that we are supporting a variety of sensors > today and that the recently added sensors have a higher maximum > distance range. > > Suggested-by: Zbyněk Kocur <[email protected]> > Signed-off-by: Andreas Klinger <[email protected]> Ideally I'm looking for Zbyněk to confirm that this addresses the original question. Thanks, Jonathan > --- > drivers/iio/proximity/srf04.c | 29 +++++++++++++++-------------- > 1 file changed, 15 insertions(+), 14 deletions(-) > > diff --git a/drivers/iio/proximity/srf04.c b/drivers/iio/proximity/srf04.c > index 8b50d56b0a03..01eb8cc63076 100644 > --- a/drivers/iio/proximity/srf04.c > +++ b/drivers/iio/proximity/srf04.c > @@ -110,7 +110,7 @@ static int srf04_read(struct srf04_data *data) > udelay(data->cfg->trigger_pulse_us); > gpiod_set_value(data->gpiod_trig, 0); > > - /* it cannot take more than 20 ms */ > + /* it should not take more than 20 ms until echo is rising */ > ret = wait_for_completion_killable_timeout(&data->rising, HZ/50); > if (ret < 0) { > mutex_unlock(&data->lock); > @@ -120,7 +120,8 @@ static int srf04_read(struct srf04_data *data) > return -ETIMEDOUT; > } > > - ret = wait_for_completion_killable_timeout(&data->falling, HZ/50); > + /* it cannot take more than 50 ms until echo is falling */ > + ret = wait_for_completion_killable_timeout(&data->falling, HZ/20); > if (ret < 0) { > mutex_unlock(&data->lock); > return ret; > @@ -135,19 +136,19 @@ static int srf04_read(struct srf04_data *data) > > dt_ns = ktime_to_ns(ktime_dt); > /* > - * measuring more than 3 meters is beyond the capabilities of > - * the sensor > + * measuring more than 6,45 meters is beyond the capabilities of > + * the supported sensors > * ==> filter out invalid results for not measuring echos of > * another us sensor > * > * formula: > - * distance 3 m > - * time = ---------- = --------- = 9404389 ns > - * speed 319 m/s > + * distance 6,45 * 2 m > + * time = ---------- = ------------ = 40438871 ns > + * speed 319 m/s > * > * using a minimum speed at -20 °C of 319 m/s > */ > - if (dt_ns > 9404389) > + if (dt_ns > 40438871) > return -EIO; > > time_ns = dt_ns; > @@ -159,20 +160,20 @@ static int srf04_read(struct srf04_data *data) > * with Temp in °C > * and speed in m/s > * > - * use 343 m/s as ultrasonic speed at 20 °C here in absence of the > + * use 343,5 m/s as ultrasonic speed at 20 °C here in absence of the > * temperature > * > * therefore: > - * time 343 > - * distance = ------ * ----- > - * 10^6 2 > + * time 343,5 time * 106 > + * distance = ------ * ------- = ------------ > + * 10^6 2 617176 > * with time in ns > * and distance in mm (one way) > * > - * because we limit to 3 meters the multiplication with 343 just > + * because we limit to 6,45 meters the multiplication with 106 just > * fits into 32 bit > */ > - distance_mm = time_ns * 343 / 2000000; > + distance_mm = time_ns * 106 / 617176; > > return distance_mm; > }
