docs: hwmon: Document bel-pfe pmbus driver

Add documentation for bel-pfe pmbus driver which supports BEL PFE1100 and
PFE3000 power supplies.
Signed-off-by: NTao Ren <rentao.bupt@gmail.com>
Link: https://lore.kernel.org/r/20191029182054.32279-3-rentao.bupt@gmail.com
[groeck: Added bel-pfe to index.rst]
Signed-off-by: NGuenter Roeck <linux@roeck-us.net>

Documentation/hwmon/bel-pfe.rst

+Kernel driver bel-pfe
+======================
+
+Supported chips:
+
+  * BEL PFE1100
+
+    Prefixes: 'pfe1100'
+
+    Addresses scanned: -
+
+    Datasheet: https://www.belfuse.com/resources/datasheets/powersolutions/ds-bps-pfe1100-12-054xa.pdf
+
+  * BEL PFE3000
+
+    Prefixes: 'pfe3000'
+
+    Addresses scanned: -
+
+    Datasheet: https://www.belfuse.com/resources/datasheets/powersolutions/ds-bps-pfe3000-series.pdf
+
+Author: Tao Ren <rentao.bupt@gmail.com>
+
+
+Description
+-----------
+
+This driver supports hardware monitoring for below power supply devices
+which support PMBus Protocol:
+
+  * BEL PFE1100
+
+    1100 Watt AC to DC power-factor-corrected (PFC) power supply.
+    PMBus Communication Manual is not publicly available.
+
+  * BEL PFE3000
+
+    3000 Watt AC/DC power-factor-corrected (PFC) and DC-DC power supply.
+    PMBus Communication Manual is not publicly available.
+
+The driver is a client driver to the core PMBus driver. Please see
+Documentation/hwmon/pmbus.rst for details on PMBus client drivers.
+
+
+Usage Notes
+-----------
+
+This driver does not auto-detect devices. You will have to instantiate the
+devices explicitly. Please see Documentation/i2c/instantiating-devices.rst for
+details.
+
+Example: the following will load the driver for an PFE3000 at address 0x20
+on I2C bus #1::
+
+	$ modprobe bel-pfe
+	$ echo pfe3000 0x20 > /sys/bus/i2c/devices/i2c-1/new_device
+
+
+Platform data support
+---------------------
+
+The driver supports standard PMBus driver platform data.
+
+
+Sysfs entries
+-------------
+
+======================= =======================================================
+curr1_label		"iin"
+curr1_input		Measured input current
+curr1_max               Input current max value
+curr1_max_alarm         Input current max alarm
+
+curr[2-3]_label		"iout[1-2]"
+curr[2-3]_input		Measured output current
+curr[2-3]_max           Output current max value
+curr[2-3]_max_alarm     Output current max alarm
+
+fan[1-2]_input          Fan 1 and 2 speed in RPM
+fan1_target             Set fan speed reference for both fans
+
+in1_label		"vin"
+in1_input		Measured input voltage
+in1_crit		Input voltage critical max value
+in1_crit_alarm		Input voltage critical max alarm
+in1_lcrit               Input voltage critical min value
+in1_lcrit_alarm         Input voltage critical min alarm
+in1_max                 Input voltage max value
+in1_max_alarm           Input voltage max alarm
+
+in2_label               "vcap"
+in2_input               Hold up capacitor voltage
+
+in[3-8]_label		"vout[1-3,5-7]"
+in[3-8]_input		Measured output voltage
+in[3-4]_alarm           vout[1-2] output voltage alarm
+
+power[1-2]_label	"pin[1-2]"
+power[1-2]_input        Measured input power
+power[1-2]_alarm	Input power high alarm
+
+power[3-4]_label	"pout[1-2]"
+power[3-4]_input	Measured output power
+
+temp[1-3]_input		Measured temperature
+temp[1-3]_alarm         Temperature alarm
+======================= =======================================================
+
+.. note::
+
+    - curr3, fan2, vout[2-7], vcap, pin2, pout2 and temp3 attributes only
+      exist for PFE3000.

Documentation/hwmon/index.rst

@@ -41,6 +41,7 @@ Hardware Monitoring Kernel Drivers
    asb100
    asc7621
    aspeed-pwm-tacho
+   bel-pfe
    coretemp
    da9052
    da9055