hwmon: sht15 humidity sensor driver

Data sheet at:
http://www.sensirion.ch/en/pdf/product_information/Datasheet-humidity-sensor-SHT1x.pdf

These sensors communicate over a 2 wire bus running a device specific
protocol.  The complexity of the driver is mainly due to handling the
substantial delays between requesting a reading and the device pulling the
data line low to indicate that the data is available.  This is handled by
an interrupt that is disabled under all other conditions.

I wasn't terribly clear on the best way to handle this, so comments on
that aspect would be particularly welcome!

Interpretation of the temperature depends on knowing the supply voltage.
If configured in a board config as a regulator consumer this is obtained
from the regulator subsystem.  If not it should be provided in the
platform data.

I've placed this driver in the hwmon subsystem as it is definitely a
device that may be used for hardware monitoring and with it's relatively
slow response times (up to 120 millisecs to get a reading) a caching
strategy certainly seems to make sense!

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/hwmon/Kconfig

@@ -692,6 +692,16 @@ config SENSORS_PCF8591
 	  These devices are hard to detect and rarely found on mainstream
 	  hardware.  If unsure, say N.
 
+config SENSORS_SHT15
+	tristate "Sensiron humidity and temperature sensors. SHT15 and compat."
+	depends on GENERIC_GPIO
+	help
+	  If you say yes here you get support for the Sensiron SHT10, SHT11,
+	  SHT15, SHT71, SHT75 humidity and temperature sensors.
+
+	  This driver can also be built as a module.  If so, the module
+	  will be called sht15.
+
 config SENSORS_SIS5595
 	tristate "Silicon Integrated Systems Corp. SiS5595"
 	depends on PCI