Re: [PATCHv2 1/3] iio: dht11: Improve reliability - be more tolerant about missing start bits

[Jonathan Cameron <jic23@kernel.org>]

On 17/01/16 16:13, Harald Geyer wrote:
> 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>
As there are no signs of other testing going on and you have clearly
hammered this reasonably hard, I'm applying it now. It'll be in my
tree until next weekend at the earliest if anyone has anything to add.

Applied to the togreg branch of iio.git - initially pushed out as
testing for the autobuilders to play with it.

Thanks,

Jonathan
> ---
> No changes since V1, but compile tested the entire series patch by patch
> additionally to test the whole series with DHT11 and DHT22 on an
> imx233-olinuxino board.
> 
>  drivers/iio/humidity/dht11.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> 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 @@ 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;
>  	}
>