This cleans up the most ugly workaround in this driver. There are no
functional changes yet in the decoding algorithm, but we improve the
following things:
* Get rid of spurious warning messages on systems with fast HRTIMER.
* If the clock is not fast enough for decoding to work, we give
up immediately.
* In that case we return EAGAIN instead of EIO, so it's easier to
discriminate causes of failure.
Returning EAGAIN is somewhat controversial: It's technically correct
as a faster clock might become available. OTOH once all clocks are
enabled this is a permanent error. There is no ECLOCKTOOSLOW error
code.
Signed-off-by: Harald Geyer <harald@xxxxxxxxx>
---
drivers/iio/humidity/dht11.c | 33 +++++++++++++++++----------------
1 files changed, 17 insertions(+), 16 deletions(-)
diff --git a/drivers/iio/humidity/dht11.c b/drivers/iio/humidity/dht11.c
index 7d79a1a..29cffa1 100644
--- a/drivers/iio/humidity/dht11.c
+++ b/drivers/iio/humidity/dht11.c
@@ -87,23 +87,11 @@ static unsigned char dht11_decode_byte(int *timing, int threshold)
return ret;
}
-static int dht11_decode(struct dht11 *dht11, int offset)
+static int dht11_decode(struct dht11 *dht11, int offset, int timeres)
{
- int i, t, timing[DHT11_BITS_PER_READ], threshold,
- timeres = DHT11_SENSOR_RESPONSE;
+ int i, t, timing[DHT11_BITS_PER_READ], threshold;
unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
- /* Calculate timestamp resolution */
- for (i = 1; i < dht11->num_edges; ++i) {
- t = dht11->edges[i].ts - dht11->edges[i-1].ts;
- if (t > 0 && t < timeres)
- timeres = t;
- }
- if (2*timeres > DHT11_DATA_BIT_HIGH) {
- pr_err("dht11: timeresolution %d too bad for decoding\n",
- timeres);
- return -EIO;
- }
threshold = DHT11_DATA_BIT_HIGH / timeres;
if (DHT11_DATA_BIT_LOW/timeres + 1 >= threshold)
pr_err("dht11: WARNING: decoding ambiguous\n");
@@ -170,10 +158,22 @@ 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;
+ int ret, timeres;
mutex_lock(&dht11->lock);
if (dht11->timestamp + DHT11_DATA_VALID_TIME < iio_get_time_ns()) {
+ timeres = iio_get_time_resolution_ns();
+ if (DHT11_DATA_BIT_HIGH < 2*timeres) {
+ dev_err(dht11->dev, "timeresolution %dns too low\n",
+ timeres);
+ /* In theory a better clock could become available
+ * at some point ... and there is no error code
+ * that really fits better.
+ */
+ ret = -EAGAIN;
+ goto err;
+ }
+
reinit_completion(&dht11->completion);
dht11->num_edges = 0;
@@ -208,7 +208,8 @@ static int dht11_read_raw(struct iio_dev *iio_dev,
ret = dht11_decode(dht11,
dht11->num_edges == DHT11_EDGES_PER_READ ?
DHT11_EDGES_PREAMBLE :
- DHT11_EDGES_PREAMBLE - 2);
+ DHT11_EDGES_PREAMBLE - 2,
+ timeres);
if (ret)
goto err;
}
--
1.7.2.5
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