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path: root/drivers/iio/proximity/srf04.c
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Diffstat (limited to 'drivers/iio/proximity/srf04.c')
-rw-r--r--drivers/iio/proximity/srf04.c29
1 files 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;
}