hwmon: Update the sysfs interface documentation
* Document the characteristics of libsensors 3.0.0 and 3.0.1. * The sysfs interface is no longer subject to changes. Signed-off-by: Jean Delvare <khali@linux-fr.org> Acked-by: Juerg Haefliger <juergh at gmail.com> Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>
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@ -2,17 +2,12 @@ Naming and data format standards for sysfs files
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The libsensors library offers an interface to the raw sensors data
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through the sysfs interface. See libsensors documentation and source for
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further information. As of writing this document, libsensors
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(from lm_sensors 2.8.3) is heavily chip-dependent. Adding or updating
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support for any given chip requires modifying the library's code.
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This is because libsensors was written for the procfs interface
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older kernel modules were using, which wasn't standardized enough.
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Recent versions of libsensors (from lm_sensors 2.8.2 and later) have
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support for the sysfs interface, though.
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The new sysfs interface was designed to be as chip-independent as
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possible.
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through the sysfs interface. Since lm-sensors 3.0.0, libsensors is
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completely chip-independent. It assumes that all the kernel drivers
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implement the standard sysfs interface described in this document.
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This makes adding or updating support for any given chip very easy, as
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libsensors, and applications using it, do not need to be modified.
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This is a major improvement compared to lm-sensors 2.
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Note that motherboards vary widely in the connections to sensor chips.
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There is no standard that ensures, for example, that the second
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@ -35,19 +30,17 @@ access this data in a simple and consistent way. That said, such programs
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will have to implement conversion, labeling and hiding of inputs. For
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this reason, it is still not recommended to bypass the library.
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If you are developing a userspace application please send us feedback on
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this standard.
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Note that this standard isn't completely established yet, so it is subject
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to changes. If you are writing a new hardware monitoring driver those
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features can't seem to fit in this interface, please contact us with your
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extension proposal. Keep in mind that backward compatibility must be
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preserved.
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Each chip gets its own directory in the sysfs /sys/devices tree. To
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find all sensor chips, it is easier to follow the device symlinks from
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/sys/class/hwmon/hwmon*.
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Up to lm-sensors 3.0.0, libsensors looks for hardware monitoring attributes
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in the "physical" device directory. Since lm-sensors 3.0.1, attributes found
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in the hwmon "class" device directory are also supported. Complex drivers
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(e.g. drivers for multifunction chips) may want to use this possibility to
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avoid namespace pollution. The only drawback will be that older versions of
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libsensors won't support the driver in question.
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All sysfs values are fixed point numbers.
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There is only one value per file, unlike the older /proc specification.
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