hwmon: (pmbus/max20830): add enable-gpio property, VOUT feedback resistor properties, and add support for max20830c/max20840c

Documentation/devicetree/bindings/hwmon/pmbus/adi,max20830.yaml

@@ -22,7 +22,13 @@ allOf:
 
 properties:
   compatible:
-    const: adi,max20830
+    oneOf:
+      - const: adi,max20830
+      - items:
+          - enum:
+              - adi,max20830c
+              - adi,max20840c
+          - const: adi,max20830  # Fallback compatible
 
   reg:
     maxItems: 1
@@ -39,16 +45,36 @@ properties:
     description:
       Optional 2.5V to 5.5V LDO input supply.
 
+  enable-gpios:
+    description:
+      GPIO connected to the EN (enable) pin.
+    maxItems: 1
+
   pwr-good-gpios:
     description:
       GPIO connected to the power-good status output pin.
     maxItems: 1
 
+  adi,vout-rfb1-ohms:
+    description:
+      Top feedback resistor (RFB1) value in ohms for VOUT sensing divider.
+      When the desired output voltage is higher than VREF, a resistor divider
+      is required. VOUT = VREF × (1 + RFB1/RFB2)
+
+  adi,vout-rfb2-ohms:
+    description:
+      Bottom feedback resistor (RFB2) value in ohms for VOUT sensing divider.
+      Datasheet recommends that RFB2 does not exceed 2.5kΩ.
+
 required:
   - compatible
   - reg
   - vddh-supply
 
+dependencies:
+  adi,vout-rfb1-ohms: ['adi,vout-rfb2-ohms']
+  adi,vout-rfb2-ohms: ['adi,vout-rfb1-ohms']
+
 unevaluatedProperties: false
 
 examples:
@@ -61,6 +87,8 @@ examples:
             compatible = "adi,max20830";
             reg = <0x30>;
             vddh-supply = <&vddh>;
+            adi,vout-rfb1-ohms = <10000>;
+            adi,vout-rfb2-ohms = <2000>;
         };
     };
 ...

Documentation/hwmon/max20830.rst

@@ -13,6 +13,22 @@ Supported chips:
 
     Datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/max20830.pdf
 
+  * Analog Devices MAX20830C
+
+    Prefix: 'max20830c'
+
+    Addresses scanned: -
+
+    Datasheet:
+
+  * Analog Devices MAX20840C
+
+    Prefix: 'max20840c'
+
+    Addresses scanned: -
+
+    Datasheet:
+
 Author:
 
   - Alexis Czezar Torreno <alexisczezar.torreno@analog.com>
@@ -21,12 +37,13 @@ Author:
 Description
 -----------
 
-This driver supports hardware monitoring for Analog Devices MAX20830
-Step-Down Switching Regulator with PMBus Interface.
+This driver supports hardware monitoring for Analog Devices MAX20830, MAX20830C
+and MAX20840C. These are Step-Down Switching Regulator with PMBus Interface.
 
-The MAX20830 is a 2.7V to 16V, 30A fully integrated step-down DC-DC switching
-regulator. Through the PMBus interface, the device can monitor input/output
-voltages, output current and temperature.
+MAX20830, and MAX20830C are 2.7V to 16V, 30A fully integrated step-down DC-DC
+switching regulators. MAX20840C is similar but can reach 40A. Through the PMBus
+interface, these devices can monitor input/output voltages, output current and
+temperature.
 
 The driver is a client driver to the core PMBus driver. Please see
 Documentation/hwmon/pmbus.rst for details on PMBus client drivers.

drivers/hwmon/pmbus/max20830.c

@@ -1,3 +1,3 @@
 // SPDX-License-Identifier: GPL-2.0
 /*
  * Hardware monitoring driver for Analog Devices MAX20830
@@ -7,12 +7,70 @@
 
 #include <linux/errno.h>
 #include <linux/i2c.h>
+#include <linux/math64.h>
+#include <linux/mod_devicetable.h>
 #include <linux/module.h>
 #include <linux/string.h>
 #include "pmbus.h"
 
 #define MAX20830_IC_DEVICE_ID_LENGTH	9
 
+struct max20830_data {
+	struct pmbus_driver_info info;
+	u32 vout_rfb1;
+	u32 vout_rfb2;
+};
+
+static const char * const supported_chip_ids[] = {
+	"MAX20830",
+	"MAX20830C",
+	"MAX20840C",
+};
+
+/*
+ * MAX20830 only supports READ_VOUT for VOUT monitoring.
+ *
+ * Limit registers (VOUT_OV_WARN_LIMIT, VOUT_OV_FAULT_LIMIT, etc.) are not
+ * supported by this driver and return -ENODATA. This means sysfs attributes
+ * like in1_max, in1_crit, etc. will not be available. Only in1_input (the
+ * scaled output voltage) is supported.
+ *
+ * MAX20830 uses an external resistor divider for voltage sensing:
+ * - VOUT_COMMAND and VOUT_MAX set the reference voltage at the feedback pin
+ * - READ_VOUT reports the feedback voltage, which needs to be scaled for actual
+ *   output voltage
+ *
+ * Scaling formula: vout_actual = vout_fb × (1 + RFB1 / RFB2)
+ *
+ * If regulator support is added in the future, some adjustments are needed to
+ * ensure correct feedback voltages are set.
+ */
+static int max20830_read_word_data(struct i2c_client *client, int page,
+				   int phase, int reg)
+{
+	const struct pmbus_driver_info *info = pmbus_get_driver_info(client);
+	const struct max20830_data *data = container_of(info, struct max20830_data, info);
+	int ret;
+	u64 temp;
+
+	switch (reg) {
+	case PMBUS_READ_VOUT:
+		ret = pmbus_read_word_data(client, page, phase, reg);
+		if (ret < 0)
+			return ret;
+
+		/* Apply voltage divider scaling if resistors are non-zero */
+		if (data->vout_rfb1 && data->vout_rfb2) {
+			temp = (u64)data->vout_rfb1 + (u64)data->vout_rfb2;
+			temp = DIV_ROUND_CLOSEST_ULL((u64)ret * temp, data->vout_rfb2);
+			ret = clamp_val(temp, 0, 0xFFFF);
+		}
+		return ret;
+	default:
+		return -ENODATA;
+	}
+}
+
 static struct pmbus_driver_info max20830_info = {
 	.pages = 1,
 	.format[PSC_VOLTAGE_IN] = linear,
@@ -23,12 +81,24 @@
 		PMBUS_HAVE_TEMP |
 		PMBUS_HAVE_STATUS_VOUT | PMBUS_HAVE_STATUS_IOUT |
 		PMBUS_HAVE_STATUS_INPUT | PMBUS_HAVE_STATUS_TEMP,
+	.read_word_data = max20830_read_word_data,
 };
 
 static int max20830_probe(struct i2c_client *client)
 {
 	u8 buf[I2C_SMBUS_BLOCK_MAX + 1] = {};
-	int ret;
+	struct max20830_data *data;
+	int i, ret;
+
+	data = devm_kzalloc(&client->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->info = max20830_info;
+
+	/* Read optional voltage divider resistor values */
+	device_property_read_u32(&client->dev, "adi,vout-rfb1-ohms", &data->vout_rfb1);
+	device_property_read_u32(&client->dev, "adi,vout-rfb2-ohms", &data->vout_rfb2);
 
 	if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_READ_BLOCK_DATA) &&
 	    !i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_READ_I2C_BLOCK))
@@ -40,13 +110,12 @@
 	 * which do not support SMBus block reads.
 	 */
 	if (i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_READ_BLOCK_DATA)) {
-		/* Reads 9 Data bytes from MAX20830 */
 		ret = i2c_smbus_read_block_data(client, PMBUS_IC_DEVICE_ID, buf);
 		if (ret < 0)
 			return dev_err_probe(&client->dev, ret,
 					     "Failed to read IC_DEVICE_ID\n");
 	} else {
-		/* Reads 1 length byte + 9 Data bytes from MAX20830 */
+		/* Reads 1 length byte + data bytes */
 		ret = i2c_smbus_read_i2c_block_data(client, PMBUS_IC_DEVICE_ID,
 						    MAX20830_IC_DEVICE_ID_LENGTH + 1,
 						    buf);
@@ -62,22 +131,27 @@
 		ret = ret - 1;
 	}
 
-	/*
-	 * MAX20830 IC_DEVICE_ID sends string data "MAX20830\0".
-	 * Return value should at least be 9 bytes of data.
-	 */
+	/* Verify we read the expected number of bytes */
 	if (ret < MAX20830_IC_DEVICE_ID_LENGTH)
 		return dev_err_probe(&client->dev, -ENODEV,
-				     "IC_DEVICE_ID too short: expected at least 9 bytes, got %d\n",
-				     ret);
+				     "IC_DEVICE_ID too short: expected %d bytes, got %d\n",
+				     MAX20830_IC_DEVICE_ID_LENGTH, ret);
+
+	/* Null-terminate the string */
+	buf[ret] = '\0';
+
+	/* Verify the device ID matches what we expect */
+	for (i = 0; i < ARRAY_SIZE(supported_chip_ids); i++) {
+		if (!strcmp(buf, supported_chip_ids[i]))
+			break;
+	}
 
-	/* 9 bytes of data, buf[0]-buf[7] = "MAX20830", buf[8] = '\0' */
-	buf[MAX20830_IC_DEVICE_ID_LENGTH - 1] = '\0';
-	if (strncmp(buf, "MAX20830", MAX20830_IC_DEVICE_ID_LENGTH - 1))
+	/* No match found - unsupported device */
+	if (i == ARRAY_SIZE(supported_chip_ids))
 		return dev_err_probe(&client->dev, -ENODEV,
-				     "Unsupported device: '%s'\n", buf);
+				     "Unsupported device: '%*pE'\n", ret, buf);
 
-	return pmbus_do_probe(client, &max20830_info);
+	return pmbus_do_probe(client, &data->info);
 }
 
 static const struct i2c_device_id max20830_id[] = {