iio: adc: hx711: optimize performance in read cycle

Set gain in hx711_reset() to its default value after a reset cycle. This
omits one precautionary read cycle, because the read is performed in
hx711_set_gain_for_channel() anyway if gain has changed.

Check for DOUT low and if its high wait some time if it goes down
instead of doing a blind reset cycle when DOUT is not down.

This is a performance optimization which allows to query the sensor with
a higher frequency.

Signed-off-by: Andreas Klinger <ak@it-klinger.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/adc/hx711.c b/drivers/iio/adc/hx711.c
index 62e6c8badd22a8d645c9edb1e0d10784157a5b61..c8686558429b9c45c9769991d1c8031607281b36 100644 (file)
--- a/drivers/iio/adc/hx711.c
+++ b/drivers/iio/adc/hx711.c
@@ -23,6 +23,7 @@
 
 /* gain to pulse and scale conversion */
 #define HX711_GAIN_MAX         3
+#define HX711_RESET_GAIN       128
 
 struct hx711_gain_to_scale {
        int                     gain;
@@ -185,8 +186,7 @@ static int hx711_wait_for_ready(struct hx711_data *hx711_data)
 
 static int hx711_reset(struct hx711_data *hx711_data)
 {
-       int ret;
-       int val = gpiod_get_value(hx711_data->gpiod_dout);
+       int val = hx711_wait_for_ready(hx711_data);
 
        if (val) {
                /*
@@ -202,22 +202,10 @@ static int hx711_reset(struct hx711_data *hx711_data)
                msleep(10);
                gpiod_set_value(hx711_data->gpiod_pd_sck, 0);
 
-               ret = hx711_wait_for_ready(hx711_data);
-               if (ret)
-                       return ret;
-               /*
-                * after a reset the gain is 128 so we do a dummy read
-                * to set the gain for the next read
-                */
-               ret = hx711_read(hx711_data);
-               if (ret < 0)
-                       return ret;
-
-               /*
-                * after a dummy read we need to wait vor readiness
-                * for not mixing gain pulses with the clock
-                */
                val = hx711_wait_for_ready(hx711_data);
+
+               /* after a reset the gain is 128 */
+               hx711_data->gain_set = HX711_RESET_GAIN;
        }
 
        return val;