iio: dht11: Improve reliability - be more tolerant about missing start bits
Instead of guessing where the data starts, we now just try to decode from
every possible start position. This causes no additional overhead if we
properly received the full preamble and only costs a few extra CPU cycles
in the case where the preamble is corrupted. This is much more efficient
than to return an error to userspace and start over again.
Signed-off-by: Harald Geyer <harald@ccbib.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/drivers/iio/humidity/dht11.c b/drivers/iio/humidity/dht11.c
index 1165b1c..1ca284a 100644
--- a/drivers/iio/humidity/dht11.c
+++ b/drivers/iio/humidity/dht11.c
@@ -161,7 +161,7 @@
int *val, int *val2, long m)
{
struct dht11 *dht11 = iio_priv(iio_dev);
- int ret, timeres;
+ int ret, timeres, offset;
mutex_lock(&dht11->lock);
if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_real_ns()) {
@@ -208,11 +208,14 @@
if (ret < 0)
goto err;
- ret = dht11_decode(dht11,
- dht11->num_edges == DHT11_EDGES_PER_READ ?
- DHT11_EDGES_PREAMBLE :
- DHT11_EDGES_PREAMBLE - 2,
- timeres);
+ offset = DHT11_EDGES_PREAMBLE +
+ dht11->num_edges - DHT11_EDGES_PER_READ;
+ for (; offset >= 0; --offset) {
+ ret = dht11_decode(dht11, offset, timeres);
+ if (!ret)
+ break;
+ }
+
if (ret)
goto err;
}