hwmon: (lm73) Add 'update_interval' attribute
The LM73 supports four A/D conversion resolutions. The default used by
the existing lm73 driver is the chip's default, 11-bit (0.25 C/LSB).
This patch enables changing of this resolution from userspace via the
update_interval sysfs attribute. Full details on usage are included in
Documentation/hwmon/lm73.
Signed-off-by: Chris Verges <kg4ysn@gmail.com>
[linux@roeck-us.net: cleanup]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
diff --git a/Documentation/hwmon/lm73 b/Documentation/hwmon/lm73
new file mode 100644
index 0000000..782b3e1
--- /dev/null
+++ b/Documentation/hwmon/lm73
@@ -0,0 +1,79 @@
+Kernel driver lm73
+==================
+
+Supported chips:
+ * Texas Instruments LM73
+ Prefix: 'lm73'
+ Addresses scanned: I2C 0x48, 0x49, 0x4a, 0x4c, 0x4d, and 0x4e
+ Datasheet: Publicly available at the Texas Instruments website
+ http://www.ti.com/product/lm73
+
+Author: Guillaume Ligneul <guillaume.ligneul@gmail.com>
+Documentation: Chris Verges <kg4ysn@gmail.com>
+
+
+Description
+-----------
+
+The LM73 is a digital temperature sensor. All temperature values are
+given in degrees Celsius.
+
+Measurement Resolution Support
+------------------------------
+
+The LM73 supports four resolutions, defined in terms of degrees C per
+LSB: 0.25, 0.125, 0.0625, and 0.3125. Changing the resolution mode
+affects the conversion time of the LM73's analog-to-digital converter.
+From userspace, the desired resolution can be specified as a function of
+conversion time via the 'update_interval' sysfs attribute for the
+device. This attribute will normalize ranges of input values to the
+maximum times defined for the resolution in the datasheet.
+
+ Resolution Conv. Time Input Range
+ (C/LSB) (msec) (msec)
+ --------------------------------------
+ 0.25 14 0..14
+ 0.125 28 15..28
+ 0.0625 56 29..56
+ 0.03125 112 57..infinity
+ --------------------------------------
+
+The following examples show how the 'update_interval' attribute can be
+used to change the conversion time:
+
+ $ echo 0 > update_interval
+ $ cat update_interval
+ 14
+ $ cat temp1_input
+ 24250
+
+ $ echo 22 > update_interval
+ $ cat update_interval
+ 28
+ $ cat temp1_input
+ 24125
+
+ $ echo 56 > update_interval
+ $ cat update_interval
+ 56
+ $ cat temp1_input
+ 24062
+
+ $ echo 85 > update_interval
+ $ cat update_interval
+ 112
+ $ cat temp1_input
+ 24031
+
+As shown here, the lm73 driver automatically adjusts any user input for
+'update_interval' via a step function. Reading back the
+'update_interval' value after a write operation will confirm the
+conversion time actively in use.
+
+Mathematically, the resolution can be derived from the conversion time
+via the following function:
+
+ g(x) = 0.250 * [log(x/14) / log(2)]
+
+where 'x' is the output from 'update_interval' and 'g(x)' is the
+resolution in degrees C per LSB.