net: phy: bcm54140: add hwmon support

The PHY supports monitoring its die temperature as well as two analog
voltages. Add support for it.
Signed-off-by: Michael Walle <michael@walle.cc>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/hwmon/bcm54140.rst

+.. SPDX-License-Identifier: GPL-2.0-only
+
+Broadcom BCM54140 Quad SGMII/QSGMII PHY
+=======================================
+
+Supported chips:
+
+   * Broadcom BCM54140
+
+     Datasheet: not public
+
+Author: Michael Walle <michael@walle.cc>
+
+Description
+-----------
+
+The Broadcom BCM54140 is a Quad SGMII/QSGMII PHY which supports monitoring
+its die temperature as well as two analog voltages.
+
+The AVDDL is a 1.0V analogue voltage, the AVDDH is a 3.3V analogue voltage.
+Both voltages and the temperature are measured in a round-robin fashion.
+
+Sysfs entries
+-------------
+
+The following attributes are supported.
+
+======================= ========================================================
+in0_label		"AVDDL"
+in0_input		Measured AVDDL voltage.
+in0_min			Minimum AVDDL voltage.
+in0_max			Maximum AVDDL voltage.
+in0_alarm		AVDDL voltage alarm.
+
+in1_label		"AVDDH"
+in1_input		Measured AVDDH voltage.
+in1_min			Minimum AVDDH voltage.
+in1_max			Maximum AVDDH voltage.
+in1_alarm		AVDDH voltage alarm.
+
+temp1_input		Die temperature.
+temp1_min		Minimum die temperature.
+temp1_max		Maximum die temperature.
+temp1_alarm		Die temperature alarm.
+======================= ========================================================

Documentation/hwmon/index.rst

@@ -42,6 +42,7 @@ Hardware Monitoring Kernel Drivers
    asb100
    asc7621
    aspeed-pwm-tacho
+   bcm54140
    bel-pfe
    coretemp
    da9052

drivers/net/phy/Kconfig

@@ -349,6 +349,7 @@ config BROADCOM_PHY
 config BCM54140_PHY
 	tristate "Broadcom BCM54140 PHY"
 	depends on PHYLIB
+	depends on HWMON || HWMON=n
 	select BCM_NET_PHYLIB
 	help
 	  Support the Broadcom BCM54140 Quad SGMII/QSGMII PHY.