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iio: dht11: Improve reliability - be more tolerant about missing start bits

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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>
This commit is contained in:
Harald Geyer 2016-01-17 16:13:29 +00:00 committed by Jonathan Cameron
parent c984b9cbbd
commit 22acc120a1
1 changed files with 9 additions and 6 deletions
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15
drivers/iio/humidity/dht11.c
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@ -161,7 +161,7 @@ static int dht11_read_raw(struct iio_dev *iio_dev,
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 @@ static int dht11_read_raw(struct iio_dev *iio_dev,
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;
}