diff --git a/Documentation/hwmon/bcm54140.rst b/Documentation/hwmon/bcm54140.rst
new file mode 100644
index 000000000000..bc6ea4b45966
--- /dev/null
+++ b/Documentation/hwmon/bcm54140.rst
@@ -0,0 +1,45 @@
+.. 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.
+======================= ========================================================
diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
index f022583f96f6..19ad0846736d 100644
--- a/Documentation/hwmon/index.rst
+++ b/Documentation/hwmon/index.rst
@@ -42,6 +42,7 @@ Hardware Monitoring Kernel Drivers
    asb100
    asc7621
    aspeed-pwm-tacho
+   bcm54140
    bel-pfe
    coretemp
    da9052
diff --git a/drivers/net/phy/Kconfig b/drivers/net/phy/Kconfig
index cb7936b577de..bacfee41b564 100644
--- a/drivers/net/phy/Kconfig
+++ b/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.
diff --git a/drivers/net/phy/bcm54140.c b/drivers/net/phy/bcm54140.c
index 0eeb60de67f8..aa854477e06a 100644
--- a/drivers/net/phy/bcm54140.c
+++ b/drivers/net/phy/bcm54140.c
@@ -6,6 +6,7 @@
 
 #include <linux/bitfield.h>
 #include <linux/brcmphy.h>
+#include <linux/hwmon.h>
 #include <linux/module.h>
 #include <linux/phy.h>
 
@@ -50,6 +51,69 @@
 #define  BCM54140_RDB_TOP_IMR_PORT1	BIT(5)
 #define  BCM54140_RDB_TOP_IMR_PORT2	BIT(6)
 #define  BCM54140_RDB_TOP_IMR_PORT3	BIT(7)
+#define BCM54140_RDB_MON_CTRL		0x831	/* monitor control */
+#define  BCM54140_RDB_MON_CTRL_V_MODE	BIT(3)	/* voltage mode */
+#define  BCM54140_RDB_MON_CTRL_SEL_MASK	GENMASK(2, 1)
+#define  BCM54140_RDB_MON_CTRL_SEL_TEMP	0	/* meassure temperature */
+#define  BCM54140_RDB_MON_CTRL_SEL_1V0	1	/* meassure AVDDL 1.0V */
+#define  BCM54140_RDB_MON_CTRL_SEL_3V3	2	/* meassure AVDDH 3.3V */
+#define  BCM54140_RDB_MON_CTRL_SEL_RR	3	/* meassure all round-robin */
+#define  BCM54140_RDB_MON_CTRL_PWR_DOWN	BIT(0)	/* power-down monitor */
+#define BCM54140_RDB_MON_TEMP_VAL	0x832	/* temperature value */
+#define BCM54140_RDB_MON_TEMP_MAX	0x833	/* temperature high thresh */
+#define BCM54140_RDB_MON_TEMP_MIN	0x834	/* temperature low thresh */
+#define  BCM54140_RDB_MON_TEMP_DATA_MASK GENMASK(9, 0)
+#define BCM54140_RDB_MON_1V0_VAL	0x835	/* AVDDL 1.0V value */
+#define BCM54140_RDB_MON_1V0_MAX	0x836	/* AVDDL 1.0V high thresh */
+#define BCM54140_RDB_MON_1V0_MIN	0x837	/* AVDDL 1.0V low thresh */
+#define  BCM54140_RDB_MON_1V0_DATA_MASK	GENMASK(10, 0)
+#define BCM54140_RDB_MON_3V3_VAL	0x838	/* AVDDH 3.3V value */
+#define BCM54140_RDB_MON_3V3_MAX	0x839	/* AVDDH 3.3V high thresh */
+#define BCM54140_RDB_MON_3V3_MIN	0x83a	/* AVDDH 3.3V low thresh */
+#define  BCM54140_RDB_MON_3V3_DATA_MASK	GENMASK(11, 0)
+#define BCM54140_RDB_MON_ISR		0x83b	/* interrupt status */
+#define  BCM54140_RDB_MON_ISR_3V3	BIT(2)	/* AVDDH 3.3V alarm */
+#define  BCM54140_RDB_MON_ISR_1V0	BIT(1)	/* AVDDL 1.0V alarm */
+#define  BCM54140_RDB_MON_ISR_TEMP	BIT(0)	/* temperature alarm */
+
+/* According to the datasheet the formula is:
+ *   T = 413.35 - (0.49055 * bits[9:0])
+ */
+#define BCM54140_HWMON_TO_TEMP(v) (413350L - (v) * 491)
+#define BCM54140_HWMON_FROM_TEMP(v) DIV_ROUND_CLOSEST_ULL(413350L - (v), 491)
+
+/* According to the datasheet the formula is:
+ *   U = bits[11:0] / 1024 * 220 / 0.2
+ *
+ * Normalized:
+ *   U = bits[11:0] / 4096 * 2514
+ */
+#define BCM54140_HWMON_TO_IN_1V0(v) ((v) * 2514 >> 11)
+#define BCM54140_HWMON_FROM_IN_1V0(v) DIV_ROUND_CLOSEST_ULL(((v) << 11), 2514)
+
+/* According to the datasheet the formula is:
+ *   U = bits[10:0] / 1024 * 880 / 0.7
+ *
+ * Normalized:
+ *   U = bits[10:0] / 2048 * 4400
+ */
+#define BCM54140_HWMON_TO_IN_3V3(v) ((v) * 4400 >> 12)
+#define BCM54140_HWMON_FROM_IN_3V3(v) DIV_ROUND_CLOSEST_ULL(((v) << 12), 4400)
+
+#define BCM54140_HWMON_TO_IN(ch, v) ((ch) ? BCM54140_HWMON_TO_IN_3V3(v) \
+					  : BCM54140_HWMON_TO_IN_1V0(v))
+#define BCM54140_HWMON_FROM_IN(ch, v) ((ch) ? BCM54140_HWMON_FROM_IN_3V3(v) \
+					    : BCM54140_HWMON_FROM_IN_1V0(v))
+#define BCM54140_HWMON_IN_MASK(ch) ((ch) ? BCM54140_RDB_MON_3V3_DATA_MASK \
+					 : BCM54140_RDB_MON_1V0_DATA_MASK)
+#define BCM54140_HWMON_IN_VAL_REG(ch) ((ch) ? BCM54140_RDB_MON_3V3_VAL \
+					    : BCM54140_RDB_MON_1V0_VAL)
+#define BCM54140_HWMON_IN_MIN_REG(ch) ((ch) ? BCM54140_RDB_MON_3V3_MIN \
+					    : BCM54140_RDB_MON_1V0_MIN)
+#define BCM54140_HWMON_IN_MAX_REG(ch) ((ch) ? BCM54140_RDB_MON_3V3_MAX \
+					    : BCM54140_RDB_MON_1V0_MAX)
+#define BCM54140_HWMON_IN_ALARM_BIT(ch) ((ch) ? BCM54140_RDB_MON_ISR_3V3 \
+					      : BCM54140_RDB_MON_ISR_1V0)
 
 #define BCM54140_DEFAULT_DOWNSHIFT 5
 #define BCM54140_MAX_DOWNSHIFT 9
@@ -57,8 +121,328 @@
 struct bcm54140_priv {
 	int port;
 	int base_addr;
+#if IS_ENABLED(CONFIG_HWMON)
+	bool pkg_init;
+	/* protect the alarm bits */
+	struct mutex alarm_lock;
+	u16 alarm;
+#endif
 };
 
+#if IS_ENABLED(CONFIG_HWMON)
+static umode_t bcm54140_hwmon_is_visible(const void *data,
+					 enum hwmon_sensor_types type,
+					 u32 attr, int channel)
+{
+	switch (type) {
+	case hwmon_in:
+		switch (attr) {
+		case hwmon_in_min:
+		case hwmon_in_max:
+			return 0644;
+		case hwmon_in_label:
+		case hwmon_in_input:
+		case hwmon_in_alarm:
+			return 0444;
+		default:
+			return 0;
+		}
+	case hwmon_temp:
+		switch (attr) {
+		case hwmon_temp_min:
+		case hwmon_temp_max:
+			return 0644;
+		case hwmon_temp_input:
+		case hwmon_temp_alarm:
+			return 0444;
+		default:
+			return 0;
+		}
+	default:
+		return 0;
+	}
+}
+
+static int bcm54140_hwmon_read_alarm(struct device *dev, unsigned int bit,
+				     long *val)
+{
+	struct phy_device *phydev = dev_get_drvdata(dev);
+	struct bcm54140_priv *priv = phydev->priv;
+	int tmp, ret = 0;
+
+	mutex_lock(&priv->alarm_lock);
+
+	/* latch any alarm bits */
+	tmp = bcm_phy_read_rdb(phydev, BCM54140_RDB_MON_ISR);
+	if (tmp < 0) {
+		ret = tmp;
+		goto out;
+	}
+	priv->alarm |= tmp;
+
+	*val = !!(priv->alarm & bit);
+	priv->alarm &= ~bit;
+
+out:
+	mutex_unlock(&priv->alarm_lock);
+	return ret;
+}
+
+static int bcm54140_hwmon_read_temp(struct device *dev, u32 attr, long *val)
+{
+	struct phy_device *phydev = dev_get_drvdata(dev);
+	u16 reg, tmp;
+
+	switch (attr) {
+	case hwmon_temp_input:
+		reg = BCM54140_RDB_MON_TEMP_VAL;
+		break;
+	case hwmon_temp_min:
+		reg = BCM54140_RDB_MON_TEMP_MIN;
+		break;
+	case hwmon_temp_max:
+		reg = BCM54140_RDB_MON_TEMP_MAX;
+		break;
+	case hwmon_temp_alarm:
+		return bcm54140_hwmon_read_alarm(dev,
+						 BCM54140_RDB_MON_ISR_TEMP,
+						 val);
+	default:
+		return -EOPNOTSUPP;
+	}
+
+	tmp = bcm_phy_read_rdb(phydev, reg);
+	if (tmp < 0)
+		return tmp;
+
+	*val = BCM54140_HWMON_TO_TEMP(tmp & BCM54140_RDB_MON_TEMP_DATA_MASK);
+
+	return 0;
+}
+
+static int bcm54140_hwmon_read_in(struct device *dev, u32 attr,
+				  int channel, long *val)
+{
+	struct phy_device *phydev = dev_get_drvdata(dev);
+	u16 bit, reg, tmp;
+
+	switch (attr) {
+	case hwmon_in_input:
+		reg = BCM54140_HWMON_IN_VAL_REG(channel);
+		break;
+	case hwmon_in_min:
+		reg = BCM54140_HWMON_IN_MIN_REG(channel);
+		break;
+	case hwmon_in_max:
+		reg = BCM54140_HWMON_IN_MAX_REG(channel);
+		break;
+	case hwmon_in_alarm:
+		bit = BCM54140_HWMON_IN_ALARM_BIT(channel);
+		return bcm54140_hwmon_read_alarm(dev, bit, val);
+	default:
+		return -EOPNOTSUPP;
+	}
+
+	tmp = bcm_phy_read_rdb(phydev, reg);
+	if (tmp < 0)
+		return tmp;
+
+	tmp &= BCM54140_HWMON_IN_MASK(channel);
+	*val = BCM54140_HWMON_TO_IN(channel, tmp);
+
+	return 0;
+}
+
+static int bcm54140_hwmon_read(struct device *dev,
+			       enum hwmon_sensor_types type, u32 attr,
+			       int channel, long *val)
+{
+	switch (type) {
+	case hwmon_temp:
+		return bcm54140_hwmon_read_temp(dev, attr, val);
+	case hwmon_in:
+		return bcm54140_hwmon_read_in(dev, attr, channel, val);
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+static const char *const bcm54140_hwmon_in_labels[] = {
+	"AVDDL",
+	"AVDDH",
+};
+
+static int bcm54140_hwmon_read_string(struct device *dev,
+				      enum hwmon_sensor_types type, u32 attr,
+				      int channel, const char **str)
+{
+	switch (type) {
+	case hwmon_in:
+		switch (attr) {
+		case hwmon_in_label:
+			*str = bcm54140_hwmon_in_labels[channel];
+			return 0;
+		default:
+			return -EOPNOTSUPP;
+		}
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+static int bcm54140_hwmon_write_temp(struct device *dev, u32 attr,
+				     int channel, long val)
+{
+	struct phy_device *phydev = dev_get_drvdata(dev);
+	u16 mask = BCM54140_RDB_MON_TEMP_DATA_MASK;
+	u16 reg;
+
+	val = clamp_val(val, BCM54140_HWMON_TO_TEMP(mask),
+			BCM54140_HWMON_TO_TEMP(0));
+
+	switch (attr) {
+	case hwmon_temp_min:
+		reg = BCM54140_RDB_MON_TEMP_MIN;
+		break;
+	case hwmon_temp_max:
+		reg = BCM54140_RDB_MON_TEMP_MAX;
+		break;
+	default:
+		return -EOPNOTSUPP;
+	}
+
+	return bcm_phy_modify_rdb(phydev, reg, mask,
+				  BCM54140_HWMON_FROM_TEMP(val));
+}
+
+static int bcm54140_hwmon_write_in(struct device *dev, u32 attr,
+				   int channel, long val)
+{
+	struct phy_device *phydev = dev_get_drvdata(dev);
+	u16 mask = BCM54140_HWMON_IN_MASK(channel);
+	u16 reg;
+
+	val = clamp_val(val, 0, BCM54140_HWMON_TO_IN(channel, mask));
+
+	switch (attr) {
+	case hwmon_in_min:
+		reg = BCM54140_HWMON_IN_MIN_REG(channel);
+		break;
+	case hwmon_in_max:
+		reg = BCM54140_HWMON_IN_MAX_REG(channel);
+		break;
+	default:
+		return -EOPNOTSUPP;
+	}
+
+	return bcm_phy_modify_rdb(phydev, reg, mask,
+				  BCM54140_HWMON_FROM_IN(channel, val));
+}
+
+static int bcm54140_hwmon_write(struct device *dev,
+				enum hwmon_sensor_types type, u32 attr,
+				int channel, long val)
+{
+	switch (type) {
+	case hwmon_temp:
+		return bcm54140_hwmon_write_temp(dev, attr, channel, val);
+	case hwmon_in:
+		return bcm54140_hwmon_write_in(dev, attr, channel, val);
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+static const struct hwmon_channel_info *bcm54140_hwmon_info[] = {
+	HWMON_CHANNEL_INFO(temp,
+			   HWMON_T_INPUT | HWMON_T_MIN | HWMON_T_MAX |
+			   HWMON_T_ALARM),
+	HWMON_CHANNEL_INFO(in,
+			   HWMON_I_INPUT | HWMON_I_MIN | HWMON_I_MAX |
+			   HWMON_I_ALARM | HWMON_I_LABEL,
+			   HWMON_I_INPUT | HWMON_I_MIN | HWMON_I_MAX |
+			   HWMON_I_ALARM | HWMON_I_LABEL),
+	NULL
+};
+
+static const struct hwmon_ops bcm54140_hwmon_ops = {
+	.is_visible = bcm54140_hwmon_is_visible,
+	.read = bcm54140_hwmon_read,
+	.read_string = bcm54140_hwmon_read_string,
+	.write = bcm54140_hwmon_write,
+};
+
+static const struct hwmon_chip_info bcm54140_chip_info = {
+	.ops = &bcm54140_hwmon_ops,
+	.info = bcm54140_hwmon_info,
+};
+
+static int bcm54140_enable_monitoring(struct phy_device *phydev)
+{
+	u16 mask, set;
+
+	/* 3.3V voltage mode */
+	set = BCM54140_RDB_MON_CTRL_V_MODE;
+
+	/* select round-robin */
+	mask = BCM54140_RDB_MON_CTRL_SEL_MASK;
+	set |= FIELD_PREP(BCM54140_RDB_MON_CTRL_SEL_MASK,
+			  BCM54140_RDB_MON_CTRL_SEL_RR);
+
+	/* remove power-down bit */
+	mask |= BCM54140_RDB_MON_CTRL_PWR_DOWN;
+
+	return bcm_phy_modify_rdb(phydev, BCM54140_RDB_MON_CTRL, mask, set);
+}
+
+/* Check if one PHY has already done the init of the parts common to all PHYs
+ * in the Quad PHY package.
+ */
+static bool bcm54140_is_pkg_init(struct phy_device *phydev)
+{
+	struct bcm54140_priv *priv = phydev->priv;
+	struct mii_bus *bus = phydev->mdio.bus;
+	int base_addr = priv->base_addr;
+	struct phy_device *phy;
+	int i;
+
+	/* Quad PHY */
+	for (i = 0; i < 4; i++) {
+		phy = mdiobus_get_phy(bus, base_addr + i);
+		if (!phy)
+			continue;
+
+		if ((phy->phy_id & phydev->drv->phy_id_mask) !=
+		    (phydev->drv->phy_id & phydev->drv->phy_id_mask))
+			continue;
+
+		priv = phy->priv;
+
+		if (priv && priv->pkg_init)
+			return true;
+	}
+
+	return false;
+}
+
+static int bcm54140_probe_once(struct phy_device *phydev)
+{
+	struct device *hwmon;
+	int ret;
+
+	/* enable hardware monitoring */
+	ret = bcm54140_enable_monitoring(phydev);
+	if (ret)
+		return ret;
+
+	hwmon = devm_hwmon_device_register_with_info(&phydev->mdio.dev,
+						     "BCM54140", phydev,
+						     &bcm54140_chip_info,
+						     NULL);
+	return PTR_ERR_OR_ZERO(hwmon);
+}
+#endif
+
 static int bcm54140_base_read_rdb(struct phy_device *phydev, u16 rdb)
 {
 	struct bcm54140_priv *priv = phydev->priv;
@@ -222,6 +606,18 @@ static int bcm54140_probe(struct phy_device *phydev)
 	if (ret)
 		return ret;
 
+#if IS_ENABLED(CONFIG_HWMON)
+	mutex_init(&priv->alarm_lock);
+
+	if (!bcm54140_is_pkg_init(phydev)) {
+		ret = bcm54140_probe_once(phydev);
+		if (ret)
+			return ret;
+	}
+
+	priv->pkg_init = true;
+#endif
+
 	phydev_dbg(phydev, "probed (port %d, base PHY address %d)\n",
 		   priv->port, priv->base_addr);
 
