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>
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@ -161,7 +161,7 @@ static int dht11_read_raw(struct iio_dev *iio_dev,
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int *val, int *val2, long m)
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{
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struct dht11 *dht11 = iio_priv(iio_dev);
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int ret, timeres;
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int ret, timeres, offset;
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mutex_lock(&dht11->lock);
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if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_real_ns()) {
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@ -208,11 +208,14 @@ static int dht11_read_raw(struct iio_dev *iio_dev,
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if (ret < 0)
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goto err;
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ret = dht11_decode(dht11,
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dht11->num_edges == DHT11_EDGES_PER_READ ?
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DHT11_EDGES_PREAMBLE :
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DHT11_EDGES_PREAMBLE - 2,
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timeres);
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offset = DHT11_EDGES_PREAMBLE +
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dht11->num_edges - DHT11_EDGES_PER_READ;
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for (; offset >= 0; --offset) {
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ret = dht11_decode(dht11, offset, timeres);
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if (!ret)
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break;
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}
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if (ret)
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goto err;
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}
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