Linux kernel stable tree https://git.rulkc.org/pub/scm/linux/kernel/git/stable/linux-stable.git/atom?h=linux-3.16.y 2017-03-16T02:27:04+00:00 2017-03-16T02:27:04+00:00 John Brooks john@fastquake.com 2017-01-18T21:50:39+00:00 urn:sha1:cac7b00f39e8b3afbe44dbc7d528e9d5061ff08b commit 5c113b5e0082e90d2e1c7b12e96a7b8cf0623e27 upstream. The DHT22 (AM2302) datasheet specifies that the LOW start pulse should not exceed 20ms. However, observations with an oscilloscope of an RPi Model 2B (rev 1.1) communicating with a DHT22 sensor showed that the driver was consistently sending start pulses longer than 20ms: Kernel 4.7.10-v7+ (n=132): Minimum pulse length: 20.20ms Maximum: 29.84ms Mean: 24.96ms StDev: 2.82ms Sensor response rate: 100% Read success rate: 76% On kernel 4.8, the start pulse was so long that the sensor would not even respond 97% of the time: Kernel 4.8.16-v7+ (n=100): Minimum pulse length: 30.4ms Maximum: 74.4ms Mean: 39.3ms StDev: 10.2ms Sensor response rate: 3% Read success rate: 3% The driver would return ETIMEDOUT and write log messages like this: [ 51.430987] dht11 dht11@0: Only 1 signal edges detected [ 66.311019] dht11 dht11@0: Only 0 signal edges detected Replacing msleep(18) with usleep_range(18000, 20000) made the pulse length sane again and restored responsiveness: Kernel 4.8.16-v7+ with usleep_range (n=123): Minimum pulse length: 18.16ms Maximum: 20.20ms Mean: 19.85ms StDev: 0.51ms Sensor response rate: 100% Read success rate: 84% Signed-off-by: John Brooks <john@fastquake.com> Reviewed-by: Harald Geyer <harald@ccbib.org> Signed-off-by: Jonathan Cameron <jic23@kernel.org> [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 2014-01-11T11:12:44+00:00 Peter Meerwald pmeerw@pmeerw.net 2014-10-01T11:03:00+00:00 urn:sha1:049973b23a6c77186dae45f708cdc0aa52b3a09e sensor provides 12-bit relative humidity and 14-bit temperature via I2C interface; temperature and linearity compensation is not implemented (yet) driver also supports the Si7015, but not the 2nd generation sensors Si7013/Si7020/Si7021 datasheet is here http://www.silabs.com/Support%20Documents/TechnicalDocs/Si7005.pdf v2: (thanks to Lars-Peter Clausen) * fix coding style * use devm_iio_device_register() * change copyright year to 2014 Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net> Reviewed-by: Lars-Peter Clausen <lars@metafoo.de> Signed-off-by: Jonathan Cameron <jic23@kernel.org> 2013-12-03T20:22:30+00:00 Harald Geyer harald@ccbib.org 2013-12-01T15:04:00+00:00 urn:sha1:091a121b04547fab2045951aff6219318ede0560 This driver handles DHT11 and DHT22 sensors. Signed-off-by: Harald Geyer <harald@ccbib.org> Signed-off-by: Jonathan Cameron <jic23@kernel.org>