Enermax ZDPMS Support
---------------------

This project is intended to provide support for the monitoring and control
logic embedded in some Enermax power supplies (notably the Enermax DigiFanless
550W).  The initial development includes a user-space proof-of-concept utility
based on the cross-platform libhidapi library, plus an experimental Linux
kernel driver to tie the ZDPMS support into the "hwmon" subsystem used by
lm-sensors.  If Enermax uses similar ZDPMS controller technology in other
power supplies, support for these other power supplies may be included in the
future.

Note that this driver is NOT maintained by Enermax or any of its subsidiaries.
I'm not affiliated with Enermax; I just bought one of their power supplies.
The name "Enermax" (and possibly "DigiFanless" and "ZDPMS") are trademark
Enermax Inc (http://www.enermax.com/).

1. What Works

The userland zdpms-config utility is apparently able to query and correctly
interpret all DC rail sensors and temperature sensors on the DigiFanless 550W,
plus the AC input voltage and the model-number string.  It can also configure
the 12V rails for single-rail or dual-rail operation with the correct
command-line options.

The kernel-land hid-zdpms driver is usable; however, in order to use it with
existing kernels, it is necessary to unbind any supported devices from the
generic HID driver.  To see if your ZDPMS controller is bound to this driver,
you can most likely look under /sys/bus/hid/drivers/hid-generic on recent
kernels such as 3.19 (older kernels might use "usb-generic" or "generic-usb"
instead of "hid-generic").  For every device bound to this driver, there will
be a symlink, named something similar to "0123:4567:89ab.cdef" to represent a
device:vendor-id:product-id.function.  Currently-supported ZDPMS controllers
will show up as "<device>:04D8:F590:<function>".  To unbind a device from this
driver, echo the symlink basename (without newlines) out to
/sys/bus/hid/drivers/hid-generic/unbind as root, i.e. 

    echo -n '0003:04D8:F590:0001' > /sys/bus/hid/drivers/hid-generic/unbind

At this point, you can load the hid-zdpms driver via insmod (or modprobe,
if it's already properly installed in your /lib/modules/ tree).  If it's
already loaded when you unbind the device from hid-generic, it will NOT
automatically bind to the zdpms driver; you will need to unload and reload
the driver, or use the device token from above as follows:

    echo -n '0003:04D8:F590:0001' > /sys/bus/hid/drivers/zdpms/bind

If/when the kernel driver gets merged with the standard Linux kernel, we
can take measures to make the above steps unnecessary, but this will require
a code change in hid-core (basically updating the "hid_have_special_driver"
list).


2. What Doesn't Work

I haven't yet figured out how to query the power factor, apparent power usage
(volt-amperes), or actual power usage (watts) on the AC input side.
Theoretically, with all the other sensor information I have, I should only need
two of these readings to extrapolate the third.