[PATCH net-next v3 0/2] net: pse-pd: Add LTC4266 PSE controller driver

[PATCH net-next v3 0/2] net: pse-pd: Add LTC4266 PSE controller driver

[Kyle Swenson]

Add support for an older PSE controller that supports powering Type 1
and Type 2 PDs.

The chip has four individually controllable power channels, each with
it own detection, classification and current-limiting abilities.  The
driver declares the static power budgeting strategy.

---
RFC v2 -> v3:
    - The admin power limit is now configurable before the port is
      powered and is independent from the class limit.  However, when a
      PD is powered, the current limit is set by the minimum between the PD's
      class and the admin power limit, to maintain compliance with the IEEE
      spec.
    - The LTC4266 doesn't support reading a port's voltage (or current)
      until that port is completely and successfully powered.  Since we
      don't have a good way to measure the port voltage, we'll first try to
      use the vpwr-supply voltage if available during probe, and fall back to
      50V (the Type 2 PSE minimum) if the regulator isn't available (ENODEV or
      EPROBE_DEFER) or doesn't have a readable voltage for the port.  This is
      the voltage the LTC4266 driver will return back to pse core when a
      port's power good bit is not set.
    - Report the hardware admin state from the "Power Enabled" bit instead
      of the "Power Good" bit.  The latter is set when the port is fully
      powered (after inrush) so a port in the process of powering up looked
      disabled to the core and had power domain budget allocated to it twice.
    - Added a Maintainers entry for the driver.
    - Avoid precision loss in pi_get_actual_pw.
    - Demote a dev_err in a common path on device disconnection to
      dev_dbg.
    - Add an err: label in map_event that'll clear all the event
      registers via the INTCLR push-button to prevent a possible
      interrupt storm.
    - The supply and over-temperature faults were too hard to test, but
      they will result in a disconnection event for one or more
      channels.  Replace those faults with a combination of a "power good"
      change and a port status check to send a disconnect event to the pse
      core.
    - Bail out of probe early if we don't have the required IRQ.
    - Replace the driver's .remove with a devm action registered before
      the controller and the IRQ to ensure the IRQ is freed before this
      driver is removed.
    - Drop reset-gpios from the binding, since the driver doesn't
      support it at the moment (because my hardware doesn't have it
      correctly wired)
    - Expand the description for sense-resistor-micro-ohms to indicate
      the property is required by the chip for accurate current limiting.

Link to RFC v2: https://lore.kernel.org/all/20260820142429.2285172-1-kyle.swenson@est.tech/

Kyle Swenson (2):
  dt-bindings: net: pse-pd: Add bindings for LTC4266 PSE Controller
  net: pse-pd: Add LTC4266 PSE controller driver

 .../bindings/net/pse-pd/lltc,ltc4266.yaml     |  180 +++
 MAINTAINERS                                   |    7 +
 drivers/net/pse-pd/Kconfig                    |   11 +
 drivers/net/pse-pd/Makefile                   |    1 +
 drivers/net/pse-pd/ltc4266.c                  | 1386 +++++++++++++++++
 5 files changed, 1585 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/net/pse-pd/lltc,ltc4266.yaml
 create mode 100644 drivers/net/pse-pd/ltc4266.c

-- 
2.55.0

[PATCH net-next v3 1/2] dt-bindings: net: pse-pd: Add bindings for LTC4266 PSE Controller

[Kyle Swenson]

Add the LTC4266 Power Sourcing Equipment controller device tree bindings
documentation.

Signed-off-by: Kyle Swenson <kyle.swenson@est.tech>
---
 .../bindings/net/pse-pd/lltc,ltc4266.yaml     | 180 ++++++++++++++++++
 1 file changed, 180 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/net/pse-pd/lltc,ltc4266.yaml

diff --git a/Documentation/devicetree/bindings/net/pse-pd/lltc,ltc4266.yaml b/Documentation/devicetree/bindings/net/pse-pd/lltc,ltc4266.yaml
new file mode 100644
index 000000000000..e11c9d601eee
--- /dev/null
+++ b/Documentation/devicetree/bindings/net/pse-pd/lltc,ltc4266.yaml
@@ -0,0 +1,180 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/net/pse-pd/lltc,ltc4266.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Linear Technology LTC4266 Power Sourcing Equipment controller
+
+maintainers:
+  - Kyle Swenson <kyle.swenson@est.tech>
+
+allOf:
+  - $ref: pse-controller.yaml#
+
+properties:
+  compatible:
+    enum:
+      - lltc,ltc4266
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  channels:
+    type: object
+    additionalProperties: false
+    description:
+      Defines the 4 physical delivery channels on the controller that can be
+      referenced by PSE PIs through their "pairsets" property. The actual port
+      matrix mapping is created when PSE PIs reference these channels in their
+      pairsets.
+
+    properties:
+      '#address-cells':
+        const: 1
+
+      '#size-cells':
+        const: 0
+
+    patternProperties:
+      '^channel@[0-3]$':
+        type: object
+        additionalProperties: false
+
+        properties:
+          reg:
+            maxItems: 1
+
+          sense-resistor-micro-ohms:
+            description: Sense resistor connected to the channel's MOSFET, used
+              for current measurement and for overcurrent detection. The I_CUT
+              and I_LIM register encodings depend on which value is fitted, so
+              a wrong value programs the wrong thresholds.
+            enum: [250000, 500000]
+
+        required:
+          - reg
+          - sense-resistor-micro-ohms
+
+    required:
+      - '#address-cells'
+      - '#size-cells'
+
+  pse-pis:
+    type: object
+    additionalProperties: false
+
+    properties:
+      '#address-cells':
+        const: 1
+
+      '#size-cells':
+        const: 0
+
+    patternProperties:
+      '^pse-pi@[0-3]$':
+        type: object
+        additionalProperties: true
+        properties:
+          pairsets:
+            description: The LTC4266 delivers power to a PI over a single
+              pairset, driven by one of the controller's four channels. There
+              is no 4-pair mode spreading a PI over two channels, so exactly
+              one channel phandle is expected.
+            maxItems: 1
+          pairset-names:
+            maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - channels
+  - pse-pis
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/irq.h>
+
+    i2c {
+      #address-cells = <1>;
+      #size-cells = <0>;
+
+      ethernet-pse@2f {
+        compatible = "lltc,ltc4266";
+        reg = <0x2f>;
+        interrupts = <8 IRQ_TYPE_LEVEL_LOW>;
+        interrupt-parent = <&gpio>;
+
+        channels {
+          #address-cells = <1>;
+          #size-cells = <0>;
+
+          phys0: channel@0 {
+            reg = <0>;
+            sense-resistor-micro-ohms = <500000>;
+          };
+
+          phys1: channel@1 {
+            reg = <1>;
+            sense-resistor-micro-ohms = <500000>;
+          };
+
+          phys2: channel@2 {
+            reg = <2>;
+            sense-resistor-micro-ohms = <500000>;
+          };
+
+          phys3: channel@3 {
+            reg = <3>;
+            sense-resistor-micro-ohms = <500000>;
+          };
+        };
+
+        pse-pis {
+          #address-cells = <1>;
+          #size-cells = <0>;
+
+          pse_pi0: pse-pi@0 {
+            reg = <0>;
+            #pse-cells = <0>;
+            pairset-names = "alternative-a";
+            pairsets = <&phys0>;
+            polarity-supported = "MDI";
+            vpwr-supply = <&vreg_pse>;
+          };
+
+          pse_pi1: pse-pi@1 {
+            reg = <1>;
+            #pse-cells = <0>;
+            pairset-names = "alternative-a";
+            pairsets = <&phys1>;
+            polarity-supported = "MDI";
+            vpwr-supply = <&vreg_pse>;
+          };
+
+          pse_pi2: pse-pi@2 {
+            reg = <2>;
+            #pse-cells = <0>;
+            pairset-names = "alternative-a";
+            pairsets = <&phys2>;
+            polarity-supported = "MDI";
+            vpwr-supply = <&vreg_pse>;
+          };
+
+          pse_pi3: pse-pi@3 {
+            reg = <3>;
+            #pse-cells = <0>;
+            pairset-names = "alternative-a";
+            pairsets = <&phys3>;
+            polarity-supported = "MDI";
+            vpwr-supply = <&vreg_pse>;
+          };
+        };
+      };
+    };
-- 
2.55.0

[PATCH net-next v3 2/2] net: pse-pd: Add LTC4266 PSE controller driver

[Kyle Swenson]

Add a new driver for the Linear Technology LTC4266 I2C Power Sourcing
Equipment controller and integrate with the PSE controller core.  The
LTC4266 supports Type 1 and Type 2 Powered Devices.

Signed-off-by: Kyle Swenson <kyle.swenson@est.tech>
---
 MAINTAINERS                  |    7 +
 drivers/net/pse-pd/Kconfig   |   11 +
 drivers/net/pse-pd/Makefile  |    1 +
 drivers/net/pse-pd/ltc4266.c | 1386 ++++++++++++++++++++++++++++++++++
 4 files changed, 1405 insertions(+)
 create mode 100644 drivers/net/pse-pd/ltc4266.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 6de1ff058db6..3f7226d04983 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -15531,10 +15531,17 @@ L:	linux-leds@vger.kernel.org
 S:	Maintained
 W:	https://ez.analog.com/linux-software-drivers
 F:	Documentation/devicetree/bindings/leds/adi,ltc3220.yaml
 F:	drivers/leds/leds-ltc3220.c
 
+LTC4266 PSE CONTROLLER DRIVER
+M:	Kyle Swenson <kyle.swenson@est.tech>
+L:	netdev@vger.kernel.org
+S:	Maintained
+F:	Documentation/devicetree/bindings/net/pse-pd/lltc,ltc4266.yaml
+F:	drivers/net/pse-pd/ltc4266.c
+
 LTC4282 HARDWARE MONITOR DRIVER
 M:	Nuno Sa <nuno.sa@analog.com>
 L:	linux-hwmon@vger.kernel.org
 S:	Supported
 F:	Documentation/devicetree/bindings/hwmon/adi,ltc4282.yaml
diff --git a/drivers/net/pse-pd/Kconfig b/drivers/net/pse-pd/Kconfig
index a0f2ae668c67..844c1b237df7 100644
--- a/drivers/net/pse-pd/Kconfig
+++ b/drivers/net/pse-pd/Kconfig
@@ -46,10 +46,21 @@ config PSE_REGULATOR
 	help
 	  This module provides support for simple regulator based Ethernet Power
 	  Sourcing Equipment without automatic classification support. For
 	  example for basic implementation of PoDL (802.3bu) specification.
 
+config PSE_LTC4266
+	tristate "LTC4266 PSE controller"
+	depends on I2C
+	select REGMAP_I2C
+	help
+	  This module provides support for LTC4266 regulator based Ethernet
+	  Power Sourcing Equipment.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called ltc4266.
+
 config PSE_PD692X0
 	tristate "PD692X0 PSE controller"
 	depends on I2C
 	select FW_LOADER
 	select FW_UPLOAD
diff --git a/drivers/net/pse-pd/Makefile b/drivers/net/pse-pd/Makefile
index 9cca5900fe34..c3fe4efcf1de 100644
--- a/drivers/net/pse-pd/Makefile
+++ b/drivers/net/pse-pd/Makefile
@@ -1,10 +1,11 @@
 # SPDX-License-Identifier: GPL-2.0-only
 # Makefile for Linux PSE drivers
 
 obj-$(CONFIG_PSE_CONTROLLER) += pse_core.o
 
+obj-$(CONFIG_PSE_LTC4266) += ltc4266.o
 obj-$(CONFIG_PSE_REALTEK_MCU) += realtek-pse-mcu-core.o
 obj-$(CONFIG_PSE_REALTEK_MCU_I2C) += realtek-pse-mcu-i2c.o
 obj-$(CONFIG_PSE_REALTEK_MCU_UART) += realtek-pse-mcu-uart.o
 obj-$(CONFIG_PSE_REGULATOR) += pse_regulator.o
 obj-$(CONFIG_PSE_PD692X0) += pd692x0.o
diff --git a/drivers/net/pse-pd/ltc4266.c b/drivers/net/pse-pd/ltc4266.c
new file mode 100644
index 000000000000..37dea467811a
--- /dev/null
+++ b/drivers/net/pse-pd/ltc4266.c
@@ -0,0 +1,1386 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Driver for Linear LTC4266 PoE PSE Controller
+ *
+ * Original work:
+ *    Copyright 2019 Cradlepoint Technology, Inc.
+ *    Cradlepoint Technology, Inc.  <source@cradlepoint.com>
+ *
+ * Re-written in 2026:
+ *    Copyright 2026 Ericsson Software Technology
+ *    Kyle Swenson <kyle.swenson@est.tech>
+ *
+ */
+
+#include <linux/bitfield.h>
+#include <linux/bits.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/errno.h>
+#include <linux/ethtool.h>
+#include <linux/i2c.h>
+#include <linux/interrupt.h>
+#include <linux/kernel.h>
+#include <linux/math.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/pse-pd/pse.h>
+#include <linux/regmap.h>
+#include <linux/regulator/consumer.h>
+#include <linux/slab.h>
+
+#define LTC4266_MAX_PORTS			4
+
+/* The minimum and maximum here depend on the resolution of the I_CUT field,
+ * which is 18.75mA.  To get 1000mW with a 50V port voltage, we need 20mA; but
+ * with 18.75 mA steps we end up with a current limit of 37.5 mA resulting in
+ * an actual power limit of 1875mW.
+ */
+#define LTC4266_PW_LIMIT_MAX			30000
+#define LTC4266_PW_LIMIT_MIN			1000
+
+/* Nominal PI voltage reported when the port is not delivering power and no
+ * "vpwr-supply" is described in the device tree: V_Port_PSE min for a Type 2
+ * PSE. IEEE 802.3-2022 Table 33-11 item 1 specifies the POWER_ON state output
+ * voltage as 50.0 V to 57.0 V for a Type 2 PSE, 44.0 V to 57.0 V for Type 1.
+ */
+#define LTC4266_VPORT_NOMINAL_UV		50000000
+
+/* Register definitions */
+#define LTC4266_REG_INTSTAT			0x00
+#define LTC4266_REG_INTMASK			0x01
+#define LTC4266_REG_PWREVN_COR			0x03
+#define LTC4266_REG_DETEVN_COR			0x05
+#define LTC4266_REG_FLTEVN_COR			0x07
+#define LTC4266_REG_TSEVN_COR			0x09
+#define LTC4266_REG_SUPEVN_COR			0x0B
+#define LTC4266_REG_STAT(_p)			(0x0C + (_p))
+#define LTC4266_REG_STATPWR			0x10
+#define LTC4266_REG_OPMD			0x12
+#define LTC4266_REG_DISENA			0x13 /* Disconnect detect enable */
+#define LTC4266_REG_MCONF			0x17
+#define LTC4266_REG_DETPB			0x18 /*PB means "push button" */
+#define LTC4266_REG_PWRPB			0x19
+#define LTC4266_REG_RSTPB			0x1A
+#define LTC4266_REG_ID				0x1B
+#define LTC4266_REG_TLIM12			0x1E
+#define LTC4266_REG_TLIM34			0x1F
+#define LTC4266_REG_IPLSB(_p)			(0x30 | ((_p) << 2))
+#define LTC4266_REG_VPLSB(_p)			(LTC4266_REG_IPLSB(_p) + 2)
+#define LTC4266_REG_HPEN			0x44
+#define LTC4266_REG_HPMD(_p)			(0x46 + (5 * (_p)))
+#define LTC4266_REG_ICUT_HP(_p)			(LTC4266_REG_HPMD(_p) + 1)
+#define LTC4266_REG_ILIM(_p)			(LTC4266_REG_HPMD(_p) + 2)
+
+/* Register field definitions */
+
+/* LTC4266_REG_INTSTAT and LTC4266_REG_INTMASK */
+#define LTC4266_INT_TSTART			BIT(6)
+#define LTC4266_INT_TCUT			BIT(5)
+#define LTC4266_INT_CLASS			BIT(4)
+#define LTC4266_INT_DETECT			BIT(3)
+#define LTC4266_INT_DIS				BIT(2)
+#define LTC4266_INT_PWRGD			BIT(1)
+
+/* Per-port event bits within the CoR event registers. Every per-port event
+ * register splits its 8 bits into a per-port low nibble and a per-port high
+ * nibble:
+ * pwrevn (03h): LO = power on/off change, HI = power good change
+ * detevn (05h): LO = detection complete, HI = classification complete
+ * fltevn (07h): LO = tCUT overcurrent,   HI = tDIS DC disconnect
+ * tsevn  (09h): LO = tSTART overcurrent, HI = tLIM current-limit timeout
+ */
+#define LTC4266_EVN_HI(_p)			BIT((_p) + 4)	/* ports 0-3 */
+#define LTC4266_EVN_LO(_p)			BIT(_p)		/* ports 0-3 */
+
+/* statp<n> (0Ch-0Fh) detection result, and the "Signature Good" value */
+#define LTC4266_PORT_CLASS(_stat)		FIELD_GET(GENMASK(6, 4), (_stat))
+#define LTC4266_PORT_DETECT(_stat)		FIELD_GET(GENMASK(2, 0), (_stat))
+#define LTC4266_DETECT_GOOD			0x4
+
+/* LTC4266_REG_STATPWR */
+#define LTC4266_STATPWR_PG(_p)			BIT((_p) + 4)
+#define LTC4266_STATPWR_PE(_p)			BIT(_p)
+
+/* LTC4266_REG_OPMD
+ * There are three other operation modes possible this
+ * driver doesn't support and so aren't defined.  The one supported mode,
+ * OPMD_SEMI, means that a port will continuously detect and classify devices,
+ * but will not power the device until instructed to do so.
+ */
+#define LTC4266_OPMD_SEMI			2
+#define LTC4266_TWO_BIT_WORD_OFFSET(_v, _p)	((_v) << ((_p) * 2))
+#define LTC4266_TWO_BIT_WORD_MASK(_p)		LTC4266_TWO_BIT_WORD_OFFSET(0x03, (_p))
+
+/* LTC4266_REG_MCONF */
+#define LTC4266_MCONF_INTERRUPT_ENABLE		BIT(7)
+/* Only report a detect event when the result changes, not every cycle */
+#define LTC4266_MCONF_DETCHG			BIT(6)
+
+/* LTC4266_REG_DETPB */
+#define LTC4266_DETPB_CLASS_ENABLE(_p)		BIT((_p) + 4)
+#define LTC4266_DETPB_DETECT_ENABLE(_p)		BIT(_p)
+
+/* LTC4266_REG_RSTPB */
+#define LTC4266_RSTPB_INTCLR			BIT(7)
+#define LTC4266_RSTPB_PINCLR			BIT(6)
+#define LTC4266_RSTPB_RSTALL			BIT(4)
+#define LTC4266_RSTPB_RSTPORTS			GENMASK(3, 0)
+
+/* LTC4266_REG_ID */
+#define LTC4266_ID				0x64
+
+/* LTC4266_REG_TLIM* */
+#define LTC4266_TLIM_VALUE			0x01
+
+/* Current-sense scaling, in nA per LSB, dependent on the sense resistor. */
+#define LTC4266_IP_NA_PER_LSB_RSENSE_025	122070	/* 122.07 uA/LSB */
+#define LTC4266_IP_NA_PER_LSB_RSENSE_050	61035	/* 61.035 uA/LSB */
+
+/* Voltage-sense scaling: 5.835 mV == 5835 uV per LSB. */
+#define LTC4266_VP_UV_PER_LSB			5835
+
+/* LTC4266_REG_HPEN, enable "High Power" mode (Type 2, Class 4) */
+#define LTC4266_HPEN(_p)			BIT(_p)
+
+/* LTC4266_REG_HPMD */
+#define LTC4266_HPMD_PONGEN			0x01
+
+/* LTC4266_REG_ICUT_HP.
+ * Set if the sense resistor specified in DT is 0.25 Ohm to have accurately
+ * scaled ICUT thresholds.
+ */
+#define LTC4266_ICUT_RSENSE_025_OHM		BIT(7)
+
+/* To keep the ICUT resolution at a constant 18.75 mA, for the 0.25 Ohm sense
+ * case we should also set this ICUT_RANGE
+ */
+#define LTC4266_ICUT_RANGE			BIT(6)
+
+/* I_CUT is programmed in a 6-bit field; each step is 18.75 mA (18750 uA). */
+#define LTC4266_ICUT_STEP_UA			18750
+#define LTC4266_ICUT_MASK			GENMASK(5, 0)
+
+/* Cap I_CUT at the suggested value for a Type 2 PD at 638mA */
+#define LTC4266_ICUT_MAX_MA			638
+#define LTC4266_ICUT_MAX_STEPS			34
+
+/* Recommended lim<n> settings from datasheet Table 5.
+ *
+ *	I_LIM (mA)	RSENSE = 0.5 Ohm	RSENSE = 0.25 Ohm
+ *	425 (Type 1)	0x00			0x80
+ *	850 (Type 2)	0x40			0xC0
+ */
+#define LTC4266_ILIM_TYPE1_RSENSE_050		0x00
+#define LTC4266_ILIM_TYPE1_RSENSE_025		0x80
+#define LTC4266_ILIM_TYPE2_RSENSE_050		0x40
+#define LTC4266_ILIM_TYPE2_RSENSE_025		0xC0
+
+enum {
+	LTC4266_READ_CURRENT = 0,
+	LTC4266_READ_VOLTAGE = 2
+};
+
+/* Map LTC4266 Classification result to PD class.  Note for a PD that has a
+ * valid detect signature, but doesn't produce a classification signature is
+ * still a valid PD.  The LTC4266 indicates this with 0x06 in the statp<n>
+ * register and calls it "Class 0".  This is a different state than when
+ * statp<n> indicates 0, which means classification isn't complete.  This maps
+ * the result to either an errno or classification value suitable for use up
+ * the stack.
+ */
+static const int ltc4266_class_map[] = {
+	-EAGAIN, /* Classification is incomplete */
+	1,
+	2,
+	3,
+	4,
+	-EINVAL,
+	0,
+	-ERANGE
+};
+
+/* Map a PD Class to I_CUT thresholds from the LTC4266 datasheet Table 2 */
+static const int ltc4266_class_to_icut[] = {
+	375,
+	112,
+	206,
+	375,
+	638
+};
+
+/* Per-class power budget at the PSE PI in mW, indexed by class (0-4).
+ * Classes 0-3 are the P_Class values from Table 33-7 in the IEEE802.3
+ * standard, which Note 1 defines as the minimum power a PSE must supply at the
+ * PI for that class (the PD input power maxima are in Table 33-18). Class 4 is
+ * P_Type, which Table 33-11 item 12 defines as I_Cable x V_Port_PSE min:
+ * 0.600 A x 50.0 V for a Type 2 PSE, with I_Cable from Table 33-1.
+ *
+ * Class 0 and Class 3 have the same value because a device without a classification
+ * signature (Class 0) has to be assumed to consume up to the maximum power for
+ * a Type 1 PD (Class 3).
+ */
+static const int ltc4266_class_pw[] = {
+	15400,	/* Class 0 */
+	4000,	/* Class 1 */
+	7000,	/* Class 2 */
+	15400,	/* Class 3 */
+	30000,	/* Class 4 (Type 2) */
+};
+
+enum sense_resistor {
+	LTC4266_RSENSE_500, /* Rsense 0.5 Ohm */
+	LTC4266_RSENSE_250 /* Rsense 0.25 Ohm */
+};
+
+struct ltc4266;
+
+/**
+ * struct ltc4266_port - per-PSE-PI context
+ *
+ * @ltc4266: the controller owning this port
+ * @chan: index of the LTC4266 delivery channel backing this PI, established
+ *	  from the PI pairset phandle by ltc4266_map_pis().  All register
+ *	  addressing uses this member.
+ * @rsense: sense resistor on @chan, used to scale current readings and
+ *	    to pick the I_CUT and I_LIM encodings.
+ * @pw_limit: Admin-configured power limit in mW, always valid: it defaults to
+ *	      LTC4266_PW_LIMIT_MAX, the most this controller can deliver, until
+ *	      pi_set_pw_limit() lowers it.
+ * @vpwr_uv: nominal PI voltage in uV, read once from the PI's "vpwr-supply" at
+ *	     probe, or LTC4266_VPORT_NOMINAL_UV when the PI does not describe
+ *	     one. Reported while the port is not delivering power, when the
+ *	     controller has nothing to measure.
+ */
+struct ltc4266_port {
+	struct ltc4266 *ltc4266;
+	u8 chan;
+	enum sense_resistor rsense;
+	int pw_limit;
+	int vpwr_uv;
+};
+
+/**
+ * struct ltc4266 - LTC4266 controller context
+ *
+ * @client: the I2C client
+ * @regmap: register map of @client
+ * @ports: table of PSE PI contexts, indexed by PSE PI id. A NULL entry is a PI
+ *	   that is not described in the device tree and therefore has no
+ *	   channel mapped.
+ * @dev: the underlying device
+ * @np: device node of @dev
+ * @pcdev: the PSE controller registered with the PSE core
+ */
+struct ltc4266 {
+	struct i2c_client *client;
+	struct regmap *regmap;
+	struct ltc4266_port *ports[LTC4266_MAX_PORTS];
+	struct device *dev;
+	struct device_node *np;
+	struct pse_controller_dev pcdev;
+};
+
+static struct ltc4266_port *ltc4266_pi_port(struct pse_controller_dev *pcdev,
+					    int id)
+{
+	struct ltc4266 *ltc4266 = container_of(pcdev, struct ltc4266, pcdev);
+
+	return ltc4266->ports[id];
+}
+
+static int ltc4266_read_iv(struct ltc4266_port *port, u8 iv)
+{
+	struct ltc4266 *ltc4266 = port->ltc4266;
+	unsigned int lsb, msb;
+	unsigned int statpwr;
+	int lsb_reg;
+	int result;
+	u64 ivbits;
+
+	result = regmap_read(ltc4266->regmap, LTC4266_REG_STATPWR, &statpwr);
+	if (result < 0)
+		return result;
+
+	/* LTC4266 IV readings are only meaningful while the port is delivering
+	 * power. When the PG (power good) bit is not set, the port is
+	 * delivering nothing, so report 0 rather than an error: returning an
+	 * errno here would abort pse_ethtool_get_status() and fail the whole
+	 * "ethtool --show-pse" query for an otherwise perfectly readable port.
+	 * Callers that must not report 0 (ltc4266_port_voltage_uv()) substitute
+	 * a nominal value.
+	 */
+	if (!(statpwr & LTC4266_STATPWR_PG(port->chan)))
+		return 0;
+
+	/* Since iv is either 0 (to read current) or 2 to (read voltage), we
+	 * can get the LSB reg by adding
+	 */
+	lsb_reg = LTC4266_REG_IPLSB(port->chan) + iv;
+
+	result = regmap_read(ltc4266->regmap, lsb_reg, &lsb);
+	if (result < 0)
+		return result;
+
+	result = regmap_read(ltc4266->regmap, lsb_reg + 1, &msb);
+	if (result < 0)
+		return result;
+
+	ivbits = (msb << 8) | lsb;
+
+	if (iv == LTC4266_READ_CURRENT)
+		if (port->rsense == LTC4266_RSENSE_250)
+			result = DIV_ROUND_CLOSEST_ULL(ivbits * LTC4266_IP_NA_PER_LSB_RSENSE_025,
+						       1000);
+		else
+			result = DIV_ROUND_CLOSEST_ULL(ivbits * LTC4266_IP_NA_PER_LSB_RSENSE_050,
+						       1000);
+	else
+		result = ivbits * LTC4266_VP_UV_PER_LSB;
+
+	return result;
+}
+
+/* Voltage at the PI in uV, if the PI is currently powering a device;
+ * otherwise, return the nominal voltage
+ */
+static int ltc4266_port_voltage_uv(struct ltc4266_port *port)
+{
+	int uv = ltc4266_read_iv(port, LTC4266_READ_VOLTAGE);
+
+	if (uv < 0)
+		return uv;
+
+	return uv ? uv : port->vpwr_uv;
+}
+
+/**
+ * ltc4266_port_set_ilim - Set the active current limit (ILIM) for a port
+ * @port: the port to configure
+ * @class: the detected PD class (0-4)
+ *
+ * Given the PD class, configure the active current limit for a particular
+ * channel.  The LTC4266 will actively enforce this current limit using the
+ * sense resistor for the channel. The values written are from the LTC4266
+ * Datasheet, Table 5, and correspond to 425mA for Type I PDs, and 850mA for
+ * Type 2 PDs (per the datasheet requirement for IEEE compliance).
+ *
+ * IEEE Std 802.3-2022, Table 33-11 specifies ILIM parameter ranges:
+ * - For Type 1 PSE operation (PD Classes 0-3):
+ * The minimum ILIM is 0.400A. This driver uses 425mA. This value fits
+ * within typical Type 1 ILIM specifications (e.g., 0.400A min to
+ * around 0.440A-0.500A max for the programmed steady-state limit).
+ *
+ * - For Type 2 PSE operation (typically PD Class 4):
+ * The minimum ILIM is 1.14 * ICable (or ~1.05 * IPort_max from other
+ * interpretations, e.g., ~0.630A to ~0.684A). This driver uses 850mA.
+ * This value meets the minimum requirement and is a supported operational
+ * current limit for high power modes in the LTC4266.
+ *
+ * The overall PSE current output must not exceed the time-dependent PSE
+ * upperbound template, IPSEUT(t), described in IEEE Std 802.3-2022,
+ * Equation (33-6). The programmed ILIM values (425mA/850mA) serve as the
+ * long-term current limit (Ilimmin segment of IPSEUT(t)) and are well
+ * within the higher short-term current allowances of that template (e.g., 1.75A).
+ *
+ * Returns: 0 on success or a negative errno.
+ */
+static int ltc4266_port_set_ilim(struct ltc4266_port *port, int class)
+{
+	bool rsense_250 = port->rsense == LTC4266_RSENSE_250;
+	u8 ilim;
+
+	if (class > 4 || class < 0)
+		return -EINVAL;
+
+	if (class < 4)
+		ilim = rsense_250 ? LTC4266_ILIM_TYPE1_RSENSE_025 :
+				    LTC4266_ILIM_TYPE1_RSENSE_050;
+	else
+		ilim = rsense_250 ? LTC4266_ILIM_TYPE2_RSENSE_025 :
+				    LTC4266_ILIM_TYPE2_RSENSE_050;
+
+	return regmap_write(port->ltc4266->regmap,
+			    LTC4266_REG_ILIM(port->chan), ilim);
+}
+
+static int ltc4266_port_set_icut(struct ltc4266_port *port, int icut)
+{
+	u8 val;
+
+	if (icut > LTC4266_ICUT_MAX_MA)
+		return -ERANGE;
+
+	val = min(DIV_ROUND_UP(icut * 1000, LTC4266_ICUT_STEP_UA),
+		  LTC4266_ICUT_MAX_STEPS) & LTC4266_ICUT_MASK;
+
+	if (port->rsense == LTC4266_RSENSE_250)
+		val |= LTC4266_ICUT_RSENSE_025_OHM | LTC4266_ICUT_RANGE;
+
+	return regmap_write(port->ltc4266->regmap,
+			    LTC4266_REG_ICUT_HP(port->chan), val);
+}
+
+/**
+ * ltc4266_pw_limit_to_icut - Convert an admin power limit to an I_CUT threshold
+ * @port: the port to convert for
+ * @max_mw: the power limit in mW
+ * @class: the detected PD class (0-4)
+ *
+ * The LTC4266 only enforces a current threshold, so a power limit has to be
+ * divided by the port voltage.
+ *
+ * Lowering I_CUT below the class threshold is legitimate: IEEE 802.3-2022
+ * 33.2.7.10 defines P_Class as either the class power or "PSE allocated power
+ * ... added to the channel power loss", and an administrative limit is that
+ * allocated power.
+ *
+ * Raising it above the class threshold is not. Table 33-11 item 7 bounds I_CUT
+ * at I_LIM, and ltc4266_port_set_ilim() picks I_LIM from the class: 425 mA for
+ * Type 1, 850 mA for Type 2. An administrative limit of LTC4266_PW_LIMIT_MAX
+ * asks for 600 mA at the nominal port voltage, which would exceed I_LIM on a
+ * Type 1 class. Capping at the class threshold from datasheet Table 2 keeps
+ * I_CUT under I_LIM for every class; the LTC4266_ICUT_MAX_MA check in
+ * ltc4266_port_set_icut() only covers Type 2.
+ *
+ * Return: the threshold in mA, or a negative errno if the voltage read failed.
+ */
+static int ltc4266_pw_limit_to_icut(struct ltc4266_port *port, int max_mw,
+				    int class)
+{
+	int uv = ltc4266_port_voltage_uv(port);
+	int icut_mA;
+
+	if (uv < 0)
+		return uv;
+
+	/* 30000 mW x 1000000 overflows an int */
+	icut_mA = DIV_ROUND_UP_ULL((u64)max_mw * 1000000, uv);
+
+	return min(ltc4266_class_to_icut[class], icut_mA);
+}
+
+static int ltc4266_port_delivering(struct ltc4266_port *port)
+{
+	unsigned int result;
+	int ret;
+
+	ret = regmap_read(port->ltc4266->regmap, LTC4266_REG_STATPWR, &result);
+	if (ret < 0)
+		return ret;
+
+	return !!((result & LTC4266_STATPWR_PG(port->chan)) &&
+		  (result & LTC4266_STATPWR_PE(port->chan)));
+}
+
+static int ltc4266_port_init(struct ltc4266_port *port)
+{
+	struct ltc4266 *ltc4266 = port->ltc4266;
+	u8 chan = port->chan;
+	u8 tlim_shift;
+	u8 tlim_mask;
+	u8 tlim_reg;
+	int ret;
+
+	/* Reset the port */
+	ret = regmap_write(ltc4266->regmap, LTC4266_REG_RSTPB, BIT(chan));
+	if (ret < 0)
+		return ret;
+
+	/* Set Semi-auto mode */
+	ret = regmap_update_bits(port->ltc4266->regmap, LTC4266_REG_OPMD,
+				 LTC4266_TWO_BIT_WORD_MASK(port->chan),
+				 LTC4266_TWO_BIT_WORD_OFFSET(LTC4266_OPMD_SEMI,
+							     port->chan));
+	if (ret < 0)
+		return ret;
+
+	/* Enable high power mode on the port (for Type 2 PD support) */
+	ret = regmap_update_bits(ltc4266->regmap, LTC4266_REG_HPEN,
+				 LTC4266_HPEN(chan), LTC4266_HPEN(chan));
+	if (ret < 0)
+		return ret;
+
+	/* Enable 2-event classification (IEEE 802.3-2022, Clause 33), which the
+	 * datasheet refers to as "Ping-Pong" classification.
+	 */
+	ret = regmap_update_bits(ltc4266->regmap, LTC4266_REG_HPMD(chan),
+				 LTC4266_HPMD_PONGEN, LTC4266_HPMD_PONGEN);
+	if (ret < 0)
+		return ret;
+
+	if (chan <= 1)
+		tlim_reg = LTC4266_REG_TLIM12;
+	else
+		tlim_reg = LTC4266_REG_TLIM34;
+
+	/* Each tlim register packs two ports: the even port in the low nibble
+	 * and the odd port in the high nibble. Shift both the value and the
+	 * mask into the correct nibble.
+	 */
+	if (chan & BIT(0))
+		tlim_shift = 4;
+	else
+		tlim_shift = 0;
+
+	tlim_mask = GENMASK(3, 0) << tlim_shift;
+
+	ret = regmap_update_bits(ltc4266->regmap, tlim_reg,
+				 tlim_mask, LTC4266_TLIM_VALUE << tlim_shift);
+	if (ret < 0)
+		return ret;
+
+	/* Enable disconnect detect. */
+	ret = regmap_update_bits(ltc4266->regmap, LTC4266_REG_DISENA,
+				 BIT(chan), BIT(chan));
+	if (ret < 0)
+		return ret;
+
+	/* Enable detection (low nibble), classification (high nibble) on the port */
+	ret = regmap_write(ltc4266->regmap, LTC4266_REG_DETPB,
+			   LTC4266_DETPB_CLASS_ENABLE(chan) |
+			   LTC4266_DETPB_DETECT_ENABLE(chan));
+
+	if (ret < 0)
+		return ret;
+
+	dev_dbg(ltc4266->dev, "Channel %d has been initialized\n", chan);
+	return 0;
+}
+
+/* Read the port's classification result and return a class 0-4 or an error if
+ * the result isn't valid.
+ */
+static int ltc4266_port_get_class(struct ltc4266_port *port)
+{
+	struct ltc4266 *ltc4266 = port->ltc4266;
+	unsigned int val;
+	int ret;
+
+	ret = regmap_read(ltc4266->regmap, LTC4266_REG_STAT(port->chan), &val);
+	if (ret < 0) {
+		dev_warn(ltc4266->dev, "Failed to read status register, err=%d\n", ret);
+		return ret;
+	}
+
+	/* Can't have a valid classification result if we've not yet had a good
+	 * detection result.
+	 */
+	if (LTC4266_PORT_DETECT(val) != LTC4266_DETECT_GOOD)
+		return -EINVAL;
+
+	ret = ltc4266_class_map[LTC4266_PORT_CLASS(val)];
+	return ret;
+}
+
+/* Maximum power the classified PD is allowed. It does not depend on the port
+ * being powered, but it does depend on the port having a PD attached and being
+ * enabled to the point of running classification and detection cycles.
+ */
+static int ltc4266_port_max_pw(struct ltc4266_port *port)
+{
+	int class = ltc4266_port_get_class(port);
+
+	if (class < 0)
+		return class;
+
+	return ltc4266_class_pw[class];
+}
+
+static int ltc4266_pi_get_pw_status(struct pse_controller_dev *pcdev, int id,
+				    struct pse_pw_status *pw_status)
+{
+	struct ltc4266_port *port = ltc4266_pi_port(pcdev, id);
+	int ret;
+
+	ret = ltc4266_port_delivering(port);
+	if (ret < 0)
+		return ret;
+
+	if (ret)
+		pw_status->c33_pw_status = ETHTOOL_C33_PSE_PW_D_STATUS_DELIVERING;
+	else
+		pw_status->c33_pw_status = ETHTOOL_C33_PSE_PW_D_STATUS_SEARCHING;
+
+	return 0;
+}
+
+/* With the static budget evaluation strategy the PSE core calls this only
+ * after a PD has been classified and the power budget has been allocated.
+ * Program the current limit for the classified PD, reduced if an admin power
+ * limit asks for less than the class is entitled to, and apply power.
+ */
+static int ltc4266_pi_enable(struct pse_controller_dev *pcdev, int id)
+{
+	struct ltc4266_port *port = ltc4266_pi_port(pcdev, id);
+	int class, icut, ret;
+
+	class = ltc4266_port_get_class(port);
+	if (class < 0)
+		return class;
+
+	ret = ltc4266_port_set_ilim(port, class);
+	if (ret < 0)
+		return ret;
+
+	/* Derive the threshold from the admin limit against the class in front of
+	 * us now, since a different PD may have been plugged in since the limit
+	 * was set.
+	 */
+	icut = ltc4266_pw_limit_to_icut(port, port->pw_limit, class);
+	if (icut < 0)
+		return icut;
+
+	ret = ltc4266_port_set_icut(port, icut);
+	if (ret < 0)
+		return ret;
+
+	/* Apply power to the port. */
+	return regmap_write(port->ltc4266->regmap, LTC4266_REG_PWRPB,
+			    BIT(port->chan));
+}
+
+static int ltc4266_pi_disable(struct pse_controller_dev *pcdev, int id)
+{
+	struct ltc4266_port *port = ltc4266_pi_port(pcdev, id);
+
+	/* Resetting the port (RSTPB, issued at the start of ltc4266_port_init)
+	 * removes power, disables detection and classification, and clears the
+	 * port's status register. Re-init the port so that detection and
+	 * classification can happen again.
+	 */
+	return ltc4266_port_init(port);
+}
+
+static int ltc4266_pi_get_voltage(struct pse_controller_dev *pcdev, int id)
+{
+	return ltc4266_port_voltage_uv(ltc4266_pi_port(pcdev, id));
+}
+
+static int ltc4266_pi_get_admin_state(struct pse_controller_dev *pcdev, int id,
+				      struct pse_admin_state *admin_state)
+{
+	struct ltc4266_port *port = ltc4266_pi_port(pcdev, id);
+	unsigned int val;
+	int ret;
+
+	/* The PSE core uses this as the hardware admin state: whether power has
+	 * been commanded on, not whether it has finished coming up.
+	 * pse_pi_is_hw_enabled() decides from it which software-enabled PIs
+	 * still need power delivery attempted, so report the power-enable
+	 * nibble (peN), which the controller sets as soon as it applies power to
+	 * the port. The power-good nibble only sets once OUT has pulled down to
+	 * VEE, up to a tSTART later, and a port reported as not enabled for that
+	 * whole ramp is one the core will allocate power domain budget for a
+	 * second time. Actual delivery is reported by pi_get_pw_status().
+	 */
+	ret = regmap_read(port->ltc4266->regmap, LTC4266_REG_STATPWR, &val);
+	if (ret < 0)
+		return ret;
+
+	if (val & LTC4266_STATPWR_PE(port->chan))
+		admin_state->c33_admin_state =
+			ETHTOOL_C33_PSE_ADMIN_STATE_ENABLED;
+	else
+		admin_state->c33_admin_state =
+			ETHTOOL_C33_PSE_ADMIN_STATE_DISABLED;
+
+	return 0;
+}
+
+static int ltc4266_pi_get_pw_class(struct pse_controller_dev *pcdev, int id)
+{
+	int ret = ltc4266_port_get_class(ltc4266_pi_port(pcdev, id));
+
+	/* ltc4266_port_get_class will return either the class, or an errno.
+	 * Returning an errno from this function will mean the ethtool command
+	 * will abort with the error and not emit later useful information.
+	 * Additionally, returning 0 to indicate no classification signature
+	 * will cause the ethtool output to omit the "Power Class" attribute
+	 * entirely. Since the "Power Class" is expected to be returned here,
+	 * and class 0 and class 3 are equivalent in terms of power allocation,
+	 * we'll return 3.
+	 */
+
+	if (ret == 0)
+		ret = 3;
+	if (ret < 0)
+		ret = 0;
+	return ret;
+}
+
+/* Get the power requested by the PD before enabling the port: its
+ * classification power.
+ */
+static int ltc4266_pi_get_pw_req(struct pse_controller_dev *pcdev, int id)
+{
+	return ltc4266_port_max_pw(ltc4266_pi_port(pcdev, id));
+}
+
+static int ltc4266_pi_get_actual_pw(struct pse_controller_dev *pcdev, int id)
+{
+	struct ltc4266_port *port = ltc4266_pi_port(pcdev, id);
+	int uA, uV;
+
+	uA = ltc4266_read_iv(port, LTC4266_READ_CURRENT);
+	if (uA < 0)
+		return uA;
+
+	uV = ltc4266_read_iv(port, LTC4266_READ_VOLTAGE);
+	if (uV < 0)
+		return uV;
+
+	/* mW = uA * uV / 1000000000 */
+	return DIV_ROUND_CLOSEST_ULL((u64)uA * uV, 1000000000);
+}
+
+/* The range of administrative power limits this controller supports. It does
+ * not depend on the detected class: the class only bounds the I_CUT threshold
+ * that ltc4266_pw_limit_to_icut() programs.
+ */
+static int ltc4266_pi_get_pw_limit_ranges(struct pse_controller_dev *pcdev, int id,
+					  struct pse_pw_limit_ranges *pw_limit_ranges)
+{
+	struct ethtool_c33_pse_pw_limit_range *c33_pw_limit_ranges;
+
+	c33_pw_limit_ranges = kzalloc_obj(*c33_pw_limit_ranges);
+	if (!c33_pw_limit_ranges)
+		return -ENOMEM;
+
+	c33_pw_limit_ranges[0].min = LTC4266_PW_LIMIT_MIN;
+	c33_pw_limit_ranges[0].max = LTC4266_PW_LIMIT_MAX;
+
+	pw_limit_ranges->c33_pw_limit_ranges = c33_pw_limit_ranges;
+
+	/* Return the number of ranges */
+	return 1;
+}
+
+/* Store the administrative power limit. The limit is independent of any PD in
+ * front of us, so accept it whether or not the port has classified anything;
+ * program I_CUT immediately when it has, so a change on a live port takes
+ * effect, and leave it to ltc4266_pi_enable() otherwise.
+ */
+static int ltc4266_pi_set_pw_limit(struct pse_controller_dev *pcdev,
+				   int id, int max_mw)
+{
+	struct ltc4266_port *port = ltc4266_pi_port(pcdev, id);
+	int class;
+	int icut;
+	int ret;
+
+	if (max_mw < LTC4266_PW_LIMIT_MIN || max_mw > LTC4266_PW_LIMIT_MAX) {
+		dev_err(port->ltc4266->dev, "power limit %d is out of range [%d, %d]\n",
+			max_mw, LTC4266_PW_LIMIT_MIN, LTC4266_PW_LIMIT_MAX);
+		return -ERANGE;
+	}
+
+	class = ltc4266_port_get_class(port);
+	if (class >= 0) {
+		icut = ltc4266_pw_limit_to_icut(port, max_mw, class);
+		if (icut < 0)
+			return icut;
+
+		ret = ltc4266_port_set_icut(port, icut);
+		if (ret < 0)
+			return ret;
+	}
+
+	port->pw_limit = max_mw;
+
+	return 0;
+}
+
+static int ltc4266_pi_get_pw_limit(struct pse_controller_dev *pcdev, int id)
+{
+	return ltc4266_pi_port(pcdev, id)->pw_limit;
+}
+
+/* Description of one delivery channel parsed out of the "channels" node. Used
+ * locally only during ltc4266_setup_pi_matrix()
+ */
+struct ltc4266_chan_desc {
+	struct device_node *np;
+	enum sense_resistor rsense;
+};
+
+static int ltc4266_get_of_channels(struct ltc4266 *ltc4266,
+				   struct ltc4266_chan_desc *chans)
+{
+	struct device_node *channels_node __free(device_node) =
+		of_get_child_by_name(ltc4266->np, "channels");
+	u32 chan_id, sense;
+	int ret;
+
+	if (!channels_node)
+		return dev_err_probe(ltc4266->dev, -EINVAL,
+				     "missing \"channels\" node\n");
+
+	for_each_child_of_node_scoped(channels_node, chan_node) {
+		if (!of_node_name_eq(chan_node, "channel"))
+			continue;
+
+		ret = of_property_read_u32(chan_node, "reg", &chan_id);
+		if (ret)
+			return dev_err_probe(ltc4266->dev, ret,
+					     "missing reg property in node %pOF\n",
+					     chan_node);
+
+		if (chan_id >= LTC4266_MAX_PORTS)
+			return dev_err_probe(ltc4266->dev, -EINVAL,
+					     "channel id %u is out of range in node %pOF\n",
+					     chan_id, chan_node);
+
+		if (chans[chan_id].np)
+			return dev_err_probe(ltc4266->dev, -EINVAL,
+					     "channel id %u is already used, please check the reg property in node %pOF\n",
+					     chan_id, chan_node);
+
+		ret = of_property_read_u32(chan_node, "sense-resistor-micro-ohms", &sense);
+		if (ret)
+			return dev_err_probe(ltc4266->dev, ret,
+					     "missing sense-resistor-micro-ohms property in node %pOF\n",
+					     chan_node);
+
+		if (sense == 250000)
+			chans[chan_id].rsense = LTC4266_RSENSE_250;
+		else if (sense == 500000)
+			chans[chan_id].rsense = LTC4266_RSENSE_500;
+		else
+			return dev_err_probe(ltc4266->dev, -EINVAL,
+					     "invalid sense resistor value %u in node %pOF\n",
+					     sense, chan_node);
+
+		chans[chan_id].np = of_node_get(chan_node);
+	}
+
+	return 0;
+}
+
+/* Find the channel a PI pairset phandle points at. */
+static int ltc4266_match_channel(const struct pse_pi_pairset *pairset,
+				 struct ltc4266_chan_desc *chans)
+{
+	int i;
+
+	for (i = 0; i < LTC4266_MAX_PORTS; i++)
+		if (pairset->np == chans[i].np)
+			return i;
+
+	return -ENODEV;
+}
+
+/*
+ * Nominal voltage of the rail feeding a PSE PI, taken from its "vpwr-supply".
+ * This is intended to work around the limitation on the LTC4266 where the port
+ * voltage is not valid until _after_ the port is powered.  Since the PSE core
+ * expects to read the port voltage when the port is not powered we need
+ * something non-zero to return to the core.
+ *
+ * In the event the regulator isn't present, or if the regulator doesn't have a
+ * nominal voltage available, we'll fall back and use 50V, which is the minimum
+ * allowed for a Type 2 PSE.
+ *
+ * Finally, we read this regulator voltage here instead of during
+ * ltc4266_pi_get_voltage to avoid deadlock.
+ *
+ * Return: the nominal voltage in uV, or LTC4266_VPORT_NOMINAL_UV if the PI
+ * describes no supply, its supply has not registered yet, or its voltage
+ * cannot be determined.
+ */
+static int ltc4266_pi_nominal_uv(struct ltc4266 *ltc4266, struct device_node *np)
+{
+	struct regulator *vpwr;
+	int uv;
+
+	vpwr = of_regulator_get_optional(ltc4266->dev, np, "vpwr");
+	if (IS_ERR(vpwr)) {
+		/* -ENODEV means the PI describes no vpwr-supply at all, which
+		 * is the case the fallback exists for. -EPROBE_DEFER means the
+		 * rail _is_ described but has not registered yet, so the
+		 * fallback is wrong for it. Asking for a probe retry is not an
+		 * option from here: we run from setup_pi_matrix(), and
+		 * pse_controller_register() unwinds neither its notification
+		 * fifo nor its pse_pi array when that fails, so every retry
+		 * would leak. Warn instead so the assumed voltage is visible.
+		 */
+		if (PTR_ERR(vpwr) == -EPROBE_DEFER)
+			dev_warn(ltc4266->dev,
+				 "%pOF: vpwr-supply is not registered yet, assuming %d uV\n",
+				 np, LTC4266_VPORT_NOMINAL_UV);
+
+		return LTC4266_VPORT_NOMINAL_UV;
+	}
+
+	uv = regulator_get_voltage(vpwr);
+	regulator_put(vpwr);
+
+	if (uv <= 0)
+		return LTC4266_VPORT_NOMINAL_UV;
+
+	return uv;
+}
+
+/* Build a port context for every PSE PI described in the device tree, bound to
+ * the channel its pairset references. A PI with no node is left NULL; the PSE
+ * core does not register a regulator for it and so never calls back for it.
+ */
+static int ltc4266_map_pis(struct ltc4266 *ltc4266,
+			   struct ltc4266_chan_desc *chans)
+{
+	struct pse_controller_dev *pcdev = &ltc4266->pcdev;
+	struct ltc4266_port *port;
+	int i, j, chan, uv;
+
+	for (i = 0; i < LTC4266_MAX_PORTS; i++) {
+		struct pse_pi *pi = &pcdev->pi[i];
+
+		if (!pi->np)
+			continue;
+
+		if (!pi->pairset[0].np)
+			return dev_err_probe(ltc4266->dev, -EINVAL,
+					     "%pOF has no pairsets\n", pi->np);
+
+		/* The LTC4266 delivers over a single pairset per channel, so
+		 * there is no 4-pair mode to spread a PI over two channels.
+		 */
+		if (pi->pairset[1].np)
+			return dev_err_probe(ltc4266->dev, -EOPNOTSUPP,
+					     "%pOF: 4-pair PSE PIs are not supported\n",
+					     pi->np);
+
+		chan = ltc4266_match_channel(&pi->pairset[0], chans);
+		if (chan < 0)
+			return dev_err_probe(ltc4266->dev, chan,
+					     "%pOF: pairset %pOF is not a channel of this controller\n",
+					     pi->np, pi->pairset[0].np);
+
+		for (j = 0; j < i; j++)
+			if (ltc4266->ports[j] && ltc4266->ports[j]->chan == chan)
+				return dev_err_probe(ltc4266->dev, -EINVAL,
+						     "%pOF: channel %d is already used by %pOF\n",
+						     pi->np, chan, pcdev->pi[j].np);
+
+		uv = ltc4266_pi_nominal_uv(ltc4266, pi->np);
+
+		port = devm_kzalloc(ltc4266->dev, sizeof(*port), GFP_KERNEL);
+		if (!port)
+			return -ENOMEM;
+
+		port->ltc4266 = ltc4266;
+		port->chan = chan;
+		port->rsense = chans[chan].rsense;
+		port->vpwr_uv = uv;
+		port->pw_limit = LTC4266_PW_LIMIT_MAX;
+		ltc4266->ports[i] = port;
+
+		dev_dbg(ltc4266->dev, "PI %d is backed by channel %d, nominal %d uV\n",
+			i, chan, uv);
+	}
+
+	return 0;
+}
+
+static int ltc4266_setup_pi_matrix(struct pse_controller_dev *pcdev)
+{
+	struct ltc4266 *ltc4266 = container_of(pcdev, struct ltc4266, pcdev);
+	struct ltc4266_chan_desc chans[LTC4266_MAX_PORTS] = { };
+	int i, ret;
+
+	if (pcdev->no_of_pse_pi)
+		return dev_err_probe(ltc4266->dev, -EINVAL,
+				     "a \"pse-pis\" node is required\n");
+
+	ret = ltc4266_get_of_channels(ltc4266, chans);
+	if (!ret)
+		ret = ltc4266_map_pis(ltc4266, chans);
+
+	for (i = 0; i < LTC4266_MAX_PORTS; i++)
+		of_node_put(chans[i].np);
+
+	if (ret)
+		return ret;
+
+	for (i = 0; i < LTC4266_MAX_PORTS; i++) {
+		if (!ltc4266->ports[i])
+			continue;
+
+		ret = ltc4266_port_init(ltc4266->ports[i]);
+		if (ret < 0)
+			return dev_err_probe(ltc4266->dev, ret,
+					     "Failed to initialize PI %d\n", i);
+	}
+
+	return 0;
+}
+
+static const struct pse_controller_ops ltc4266_ops = {
+	.setup_pi_matrix = ltc4266_setup_pi_matrix,
+	.pi_get_admin_state = ltc4266_pi_get_admin_state,
+	.pi_get_pw_status = ltc4266_pi_get_pw_status,
+	.pi_get_pw_class = ltc4266_pi_get_pw_class,
+	.pi_get_actual_pw = ltc4266_pi_get_actual_pw,
+	.pi_enable = ltc4266_pi_enable,
+	.pi_disable = ltc4266_pi_disable,
+	.pi_get_voltage = ltc4266_pi_get_voltage,
+	.pi_get_pw_limit = ltc4266_pi_get_pw_limit,
+	.pi_set_pw_limit = ltc4266_pi_set_pw_limit,
+	.pi_get_pw_limit_ranges = ltc4266_pi_get_pw_limit_ranges,
+	.pi_get_pw_req = ltc4266_pi_get_pw_req,
+};
+
+#define LTC4266_INTERRUPT_SOURCES	(LTC4266_INT_TSTART | LTC4266_INT_TCUT | \
+					 LTC4266_INT_CLASS | LTC4266_INT_DETECT | \
+					 LTC4266_INT_DIS | LTC4266_INT_PWRGD)
+
+static int ltc4266_enable_interrupts(struct ltc4266 *ltc4266)
+{
+	/* Unmask interrupts */
+	return regmap_write(ltc4266->regmap, LTC4266_REG_INTMASK,
+		     LTC4266_INTERRUPT_SOURCES);
+}
+
+static int ltc4266_disable_interrupts(struct ltc4266 *ltc4266)
+{
+	int ret;
+
+	ret = regmap_write(ltc4266->regmap, LTC4266_REG_INTMASK, 0x00);
+	if (ret < 0)
+		return ret;
+
+	/* Reset the (SMBus Alert) interrupt pin */
+	return regmap_write(ltc4266->regmap, LTC4266_REG_RSTPB, LTC4266_RSTPB_PINCLR);
+}
+
+static int ltc4266_map_event(int irq, struct pse_controller_dev *pcdev,
+			     unsigned long *notifs, unsigned long *notifs_mask)
+{
+	struct ltc4266 *ltc4266 = container_of(pcdev, struct ltc4266, pcdev);
+	unsigned int detevn = 0, fltevn = 0, tsevn = 0, pwrevn = 0;
+	unsigned int statpwr = 0;
+	unsigned int intstat;
+	int ret;
+	int i;
+
+	ret = ltc4266_disable_interrupts(ltc4266);
+	if (ret < 0)
+		goto err;
+
+	ret = regmap_read(ltc4266->regmap, LTC4266_REG_INTSTAT, &intstat);
+	if (ret < 0)
+		goto err;
+
+	if (!intstat)
+		goto done;
+
+	if (intstat & LTC4266_INT_PWRGD) {
+		ret = regmap_read(ltc4266->regmap, LTC4266_REG_PWREVN_COR, &pwrevn);
+		if (ret < 0) {
+			dev_err(&ltc4266->client->dev, "Failed to read pwrevn, err=%d\n", ret);
+			goto err;
+		}
+
+		ret = regmap_read(ltc4266->regmap, LTC4266_REG_STATPWR, &statpwr);
+		if (ret < 0) {
+			dev_err(&ltc4266->client->dev, "Failed to read statpwr, err=%d\n", ret);
+			goto err;
+		}
+	}
+
+	if (intstat & (LTC4266_INT_DIS | LTC4266_INT_TCUT)) {
+		ret = regmap_read(ltc4266->regmap, LTC4266_REG_FLTEVN_COR, &fltevn);
+		if (ret < 0) {
+			dev_err(&ltc4266->client->dev, "Failed to read fltevn err=%d\n", ret);
+			goto err;
+		}
+	}
+
+	if (intstat & (LTC4266_INT_TSTART | LTC4266_INT_TCUT)) {
+		ret = regmap_read(ltc4266->regmap, LTC4266_REG_TSEVN_COR, &tsevn);
+		if (ret < 0) {
+			dev_err(&ltc4266->client->dev, "Failed to read tsevn, err=%d\n", ret);
+			goto err;
+		}
+	}
+
+	if (intstat & (LTC4266_INT_CLASS | LTC4266_INT_DETECT)) {
+		ret = regmap_read(ltc4266->regmap, LTC4266_REG_DETEVN_COR, &detevn);
+		if (ret < 0) {
+			dev_err(&ltc4266->client->dev, "Failed to read detevn, err=%d\n", ret);
+			goto err;
+		}
+	}
+
+	/* The event registers are indexed by delivery channel while notifs[] is
+	 * indexed by PSE PI id, so walk the PIs and use each one's channel to
+	 * select the event bits.
+	 */
+	for (i = 0; i < LTC4266_MAX_PORTS; i++) {
+		struct ltc4266_port *port = ltc4266->ports[i];
+		unsigned int fault;
+		bool pg_lost;
+		u8 chan;
+
+		if (!port)
+			continue;
+
+		chan = port->chan;
+
+		fault = (tsevn | fltevn) &
+			(LTC4266_EVN_HI(chan) | LTC4266_EVN_LO(chan));
+
+		/* The controller also drops a port without reporting any
+		 * per-port fault event, for instance on an over-temperature
+		 * shutdown or when it finds a failed external MOSFET. Both of
+		 * those clear the port's detection and classification enables,
+		 * so the port stays dark until it is re-initialised. A power
+		 * good change that leaves statpwr[pg] clear catches them, and
+		 * ignores the rising edge of a port that has just been powered
+		 * on.
+		 */
+		pg_lost = (pwrevn & LTC4266_EVN_HI(chan)) &&
+			  !(statpwr & LTC4266_STATPWR_PG(chan));
+
+		if (fault || pg_lost) {
+			/* The port has gone down; if we see this, then we don't
+			 * care if any of the remaining events are set.  If the
+			 * device did disconnect briefly, it'll redetect and
+			 * reclassify accordingly
+			 */
+			notifs[i] |= ETHTOOL_C33_PSE_EVENT_DISCONNECTION;
+			*notifs_mask |= BIT(i);
+
+			/* Report over-current if the port went down for any
+			 * overcurrent reason: tSTART (tsevn low nibble, startup
+			 * inrush), tLIM (tsevn high nibble, current-limit
+			 * timeout) or tCUT (fltevn low nibble, I_CUT timeout).
+			 */
+			if ((tsevn & (LTC4266_EVN_LO(chan) | LTC4266_EVN_HI(chan))) ||
+			    (fltevn & LTC4266_EVN_LO(chan)))
+				notifs[i] |= ETHTOOL_PSE_EVENT_OVER_CURRENT;
+
+			dev_dbg(&ltc4266->client->dev,
+				"tsevn=0x%02X fltevn=0x%02X pwrevn=0x%02X statpwr=0x%02X\n",
+				tsevn, fltevn, pwrevn, statpwr);
+			continue;
+		}
+		if (detevn & LTC4266_EVN_LO(chan)) {
+			/* Read the detect result, and if it isn't detect good,
+			 * call it a disconnect
+			 */
+			unsigned int detval;
+
+			ret = regmap_read(ltc4266->regmap, LTC4266_REG_STAT(chan), &detval);
+			if (ret < 0) {
+				dev_warn(ltc4266->dev, "Failed to read status register, err=%d\n",
+					 ret);
+				continue;
+			}
+
+			if (LTC4266_PORT_DETECT(detval) != LTC4266_DETECT_GOOD) {
+				notifs[i] |= ETHTOOL_C33_PSE_EVENT_DISCONNECTION;
+				*notifs_mask |= BIT(i);
+				continue;
+			}
+		}
+
+		if (detevn & LTC4266_EVN_HI(chan)) {
+			int class = ltc4266_port_get_class(port);
+
+			if (class >= 0) {
+				notifs[i] |= ETHTOOL_C33_PSE_EVENT_CLASSIFICATION;
+				*notifs_mask |= BIT(i);
+			}
+		}
+	}
+
+done:
+	return ltc4266_enable_interrupts(ltc4266);
+
+err:
+	/* (Attempt to) clear any remaining event registers that we might've
+	 * missed in the event a previous read has failed.
+	 */
+	ret = regmap_write(ltc4266->regmap, LTC4266_REG_RSTPB, LTC4266_RSTPB_INTCLR);
+	if (ret)
+		dev_warn(&ltc4266->client->dev, "Failed to clear pending interrupts, err=%d\n",
+			 ret);
+
+	return ltc4266_enable_interrupts(ltc4266);
+}
+
+static const struct regmap_config ltc4266_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = 0x5F,
+};
+
+static void ltc4266_teardown(void *data)
+{
+	struct ltc4266 *ltc4266 = data;
+
+	ltc4266_disable_interrupts(ltc4266);
+
+	/* Prevent the chip from asserting interrupts */
+	regmap_update_bits(ltc4266->regmap, LTC4266_REG_MCONF,
+			   LTC4266_MCONF_INTERRUPT_ENABLE, 0);
+
+	/* Reset all the ports and do not re-init: a port reset removes power and
+	 * clears the port's detection and classification enables, leaving it in
+	 * semi-auto mode, which never powers a port without a host request.
+	 */
+	regmap_write(ltc4266->regmap, LTC4266_REG_RSTPB, LTC4266_RSTPB_RSTPORTS);
+}
+
+static int ltc4266_probe(struct i2c_client *client)
+{
+	struct ltc4266 *ltc4266;
+	struct regmap *regmap;
+	unsigned int id_reg;
+	int ret;
+
+	struct pse_irq_desc irq_desc = {
+		.name = "ltc4266-irq",
+		.map_event = ltc4266_map_event,
+	};
+
+	/* We need IRQ for static power budgeting and if don't have it, fail
+	 * probe early
+	 */
+	if (!client->irq)
+		return dev_err_probe(&client->dev, -EINVAL,
+				     "Interrupt is required for power budget management\n");
+
+	regmap = devm_regmap_init_i2c(client, &ltc4266_regmap_config);
+	if (IS_ERR(regmap))
+		return dev_err_probe(&client->dev, PTR_ERR(regmap),
+				     "Failed to allocate regmap\n");
+
+	/* Confirm we are talking to an LTC4266: the id register (0x1B) should
+	 * read back its documented reset value of 0x64.
+	 */
+	ret = regmap_read(regmap, LTC4266_REG_ID, &id_reg);
+	if (ret < 0)
+		return dev_err_probe(&client->dev, ret, "Failed to read ID register\n");
+
+	if (id_reg != LTC4266_ID)
+		return dev_err_probe(&client->dev, -ENODEV,
+				     "Expected an ID of 0x64, saw 0x%02X\n", id_reg);
+
+	/* Reset the chip */
+	ret = regmap_write(regmap, LTC4266_REG_RSTPB, LTC4266_RSTPB_INTCLR | LTC4266_RSTPB_RSTALL);
+	if (ret < 0)
+		return dev_err_probe(&client->dev, ret, "Failed to reset\n");
+
+	/* LTC4266 requires approximately 10 ms after reset to be stable; if it
+	 * isn't, then there is typically an undervoltage lockout/something pretty bad
+	 * going on. We give it 50 ms here so we don't need to poll the chip and use I2C bandwidth
+	 */
+	msleep(50);
+
+	/* Let's make sure the chip came out of reset (if not, the chip is probably
+	 * either (no longer?) present, in thermal shutdown, or watchdogged....either
+	 * way, there's nothing we can do in software to fix it)
+	 */
+	ret = regmap_read(regmap, LTC4266_REG_ID, &id_reg);
+	if (ret < 0)
+		return dev_err_probe(&client->dev, ret,
+				     "Failed to re-read ID register after reset\n");
+
+	if (id_reg != LTC4266_ID)
+		return dev_err_probe(&client->dev, -ENODEV,
+				     "Failed to re-read device ID after reset 0x%02X\n",
+				     id_reg);
+
+	ltc4266 = devm_kzalloc(&client->dev, sizeof(struct ltc4266), GFP_KERNEL);
+	if (!ltc4266)
+		return -ENOMEM;
+
+	ltc4266->client = client;
+	ltc4266->regmap = regmap;
+	ltc4266->np = client->dev.of_node;
+	ltc4266->dev = &client->dev;
+
+	/* After reset, the LTC4266 will interrupt with a (single) supply fault.
+	 * Clear it here and discard the result
+	 */
+	regmap_read(ltc4266->regmap, LTC4266_REG_SUPEVN_COR, &id_reg);
+
+	ret = ltc4266_disable_interrupts(ltc4266);
+	if (ret)
+		return dev_err_probe(&client->dev, ret,
+				     "Failed to disable interrupts\n");
+
+	/* Registered before the controller and the IRQ so devres ordering runs
+	 * it after free_irq() and pse_controller_unregister(), and so a failed
+	 * probe cannot leave ports running detection with no driver bound.
+	 */
+	ret = devm_add_action_or_reset(&client->dev, ltc4266_teardown, ltc4266);
+	if (ret)
+		return ret;
+
+	ltc4266->pcdev.owner = THIS_MODULE;
+	ltc4266->pcdev.ops = &ltc4266_ops;
+	ltc4266->pcdev.dev = &client->dev;
+	ltc4266->pcdev.types = ETHTOOL_PSE_C33;
+	ltc4266->pcdev.nr_lines = LTC4266_MAX_PORTS;
+	ltc4266->pcdev.supp_budget_eval_strategies = PSE_BUDGET_EVAL_STRAT_STATIC;
+
+	ret = devm_pse_controller_register(ltc4266->dev, &ltc4266->pcdev);
+	if (ret)
+		return dev_err_probe(&client->dev, ret,
+				     "Failed to register PSE controller\n");
+
+	/* Enable the interrupt pin, and only report detect events on
+	 * change (detchg) so idle ports continuously re-running
+	 * detection in semi-auto mode don't flood the host with a
+	 * detect event every cycle.
+	 */
+	ret = regmap_update_bits(ltc4266->regmap, LTC4266_REG_MCONF,
+				 LTC4266_MCONF_INTERRUPT_ENABLE | LTC4266_MCONF_DETCHG,
+				 LTC4266_MCONF_INTERRUPT_ENABLE | LTC4266_MCONF_DETCHG);
+	if (ret)
+		return dev_err_probe(&client->dev, ret,
+				     "Failed to configure interrupts\n");
+
+	ret = devm_pse_irq_helper(&ltc4266->pcdev, client->irq,
+				  0, &irq_desc);
+	if (ret)
+		return dev_err_probe(&client->dev, ret,
+				     "Failed to register PSE IRQ\n");
+
+	/* Unmask the chip interrupt sources now the handler is ready. */
+	ret = ltc4266_enable_interrupts(ltc4266);
+	if (ret)
+		return dev_err_probe(&client->dev, ret,
+				     "Failed to enable interrupts\n");
+
+	return 0;
+}
+
+static const struct i2c_device_id ltc4266_id[] = {
+	{.name = "ltc4266"},
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, ltc4266_id);
+
+static const struct of_device_id ltc4266_of_match[] = {
+	{ .compatible = "lltc,ltc4266" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, ltc4266_of_match);
+
+static struct i2c_driver ltc4266_driver = {
+	.driver		= {
+		.name	= "ltc4266",
+		.of_match_table = ltc4266_of_match,
+	},
+	.probe		= ltc4266_probe,
+	.id_table	= ltc4266_id,
+};
+module_i2c_driver(ltc4266_driver);
+
+MODULE_AUTHOR("Kyle Swenson <kyle.swenson@est.tech>");
+MODULE_DESCRIPTION("LTC4266 PoE PSE Controller Driver");
+MODULE_LICENSE("GPL");
-- 
2.55.0