[PATCH] hwmon: Sysfs interface documentation update, 2 of 2, take 2

Reword and complete certain parts of the hwmon sysfs-interface
documentation file. Hopefully this will make things clearer for new
driver authors.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 29 insertions, 16 deletions

diff --git a/Documentation/hwmon/sysfs-interface b/Documentation/hwmon/sysfs-interface
index bc59a5113d1..d1d390aaf62 100644
--- a/Documentation/hwmon/sysfs-interface
+++ b/Documentation/hwmon/sysfs-interface
@@ -3,15 +3,15 @@ Naming and data format standards for sysfs files
 
 The libsensors library offers an interface to the raw sensors data
 through the sysfs interface. See libsensors documentation and source for
-more further information. As of writing this document, libsensors
-(from lm_sensors 2.8.3) is heavily chip-dependant. Adding or updating
+further information. As of writing this document, libsensors
+(from lm_sensors 2.8.3) is heavily chip-dependent. Adding or updating
 support for any given chip requires modifying the library's code.
 This is because libsensors was written for the procfs interface
 older kernel modules were using, which wasn't standardized enough.
 Recent versions of libsensors (from lm_sensors 2.8.2 and later) have
 support for the sysfs interface, though.
 
-The new sysfs interface was designed to be as chip-independant as
+The new sysfs interface was designed to be as chip-independent as
 possible.
 
 Note that motherboards vary widely in the connections to sensor chips.
@@ -24,7 +24,7 @@ range using external resistors. Since the values of these resistors
 can change from motherboard to motherboard, the conversions cannot be
 hard coded into the driver and have to be done in user space.
 
-For this reason, even if we aim at a chip-independant libsensors, it will
+For this reason, even if we aim at a chip-independent libsensors, it will
 still require a configuration file (e.g. /etc/sensors.conf) for proper
 values conversion, labeling of inputs and hiding of unused inputs.
 
@@ -39,15 +39,16 @@ If you are developing a userspace application please send us feedback on
 this standard.
 
 Note that this standard isn't completely established yet, so it is subject
-to changes, even important ones. One more reason to use the library instead
-of accessing sysfs files directly.
+to changes. If you are writing a new hardware monitoring driver those
+features can't seem to fit in this interface, please contact us with your
+extension proposal. Keep in mind that backward compatibility must be
+preserved.
 
 Each chip gets its own directory in the sysfs /sys/devices tree.  To
-find all sensor chips, it is easier to follow the symlinks from
-/sys/i2c/devices/
+find all sensor chips, it is easier to follow the device symlinks from
+/sys/class/hwmon/hwmon*.
 
-All sysfs values are fixed point numbers.  To get the true value of some
-of the values, you should divide by the specified value.
+All sysfs values are fixed point numbers.
 
 There is only one value per file, unlike the older /proc specification.
 The common scheme for files naming is: <type><number>_<item>. Usual
@@ -77,6 +78,9 @@ RW	read/write value
 Read/write values may be read-only for some chips, depending on the
 hardware implementation.
 
+All entries are optional, and should only be created in a given driver
+if the chip has the feature.
+
 ************
 * Voltages *
 ************
@@ -213,32 +217,32 @@ temp[1-*]_type	Sensor type selection.
 		Not all types are supported by all chips
 
 temp[1-*]_max	Temperature max value.
-		Unit: millidegree Celcius
+		Unit: millidegree Celsius (or millivolt, see below)
 		RW
 
 temp[1-*]_min	Temperature min value.
-		Unit: millidegree Celcius
+		Unit: millidegree Celsius
 		RW
 
 temp[1-*]_max_hyst
 		Temperature hysteresis value for max limit.
-		Unit: millidegree Celcius
+		Unit: millidegree Celsius
 		Must be reported as an absolute temperature, NOT a delta
 		from the max value.
 		RW
 
 temp[1-*]_input Temperature input value.
-		Unit: millidegree Celcius
+		Unit: millidegree Celsius
 		RO
 
 temp[1-*]_crit	Temperature critical value, typically greater than
 		corresponding temp_max values.
-		Unit: millidegree Celcius
+		Unit: millidegree Celsius
 		RW
 
 temp[1-*]_crit_hyst
 		Temperature hysteresis value for critical limit.
-		Unit: millidegree Celcius
+		Unit: millidegree Celsius
 		Must be reported as an absolute temperature, NOT a delta
 		from the critical value.
 		RW
@@ -256,6 +260,15 @@ temp[1-4]_offset
 		itself, for example the thermal diode inside the CPU or
 		a thermistor nearby.
 
+Some chips measure temperature using external thermistors and an ADC, and
+report the temperature measurement as a voltage. Converting this voltage
+back to a temperature (or the other way around for limits) requires
+mathematical functions not available in the kernel, so the conversion
+must occur in user space. For these chips, all temp* files described
+above should contain values expressed in millivolt instead of millidegree
+Celsius. In other words, such temperature channels are handled as voltage
+channels by the driver.
+
 Also see the Alarms section for status flags associated with temperatures.