pmbus: Add driver for Maxim MAX31785 Intelligent Fan Controller

The Maxim MAX31785 is a PMBus device providing closed-loop, multi-channel
fan management with temperature and remote voltage sensing. It supports
various fan control features, including PWM frequency control, temperature
hysteresis, dual tachometer measurements, and fan health monitoring.

This patch presents a basic driver using only the existing features of the
PMBus subsystem.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
[groeck: Modified description to clarify that fan control is not yet provided]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/max31785

@@ -0,0 +1,51 @@
+Kernel driver max31785
+======================
+
+Supported chips:
+  * Maxim MAX31785, MAX31785A
+    Prefix: 'max31785' or 'max31785a'
+    Addresses scanned: -
+    Datasheet: https://datasheets.maximintegrated.com/en/ds/MAX31785.pdf
+
+Author: Andrew Jeffery <andrew@aj.id.au>
+
+Description
+-----------
+
+The Maxim MAX31785 is a PMBus device providing closed-loop, multi-channel fan
+management with temperature and remote voltage sensing. Various fan control
+features are provided, including PWM frequency control, temperature hysteresis,
+dual tachometer measurements, and fan health monitoring.
+
+For dual rotor fan configuration, the MAX31785 exposes the slowest rotor of the
+two in the fan[1-4]_input attributes.
+
+Usage Notes
+-----------
+
+This driver does not probe for PMBus devices. You will have to instantiate
+devices explicitly.
+
+Sysfs attributes
+----------------
+
+fan[1-4]_alarm		Fan alarm.
+fan[1-4]_fault		Fan fault.
+fan[1-4]_input		Fan RPM.
+
+in[1-6]_crit		Critical maximum output voltage
+in[1-6]_crit_alarm	Output voltage critical high alarm
+in[1-6]_input		Measured output voltage
+in[1-6]_label		"vout[18-23]"
+in[1-6]_lcrit		Critical minimum output voltage
+in[1-6]_lcrit_alarm	Output voltage critical low alarm
+in[1-6]_max		Maximum output voltage
+in[1-6]_max_alarm	Output voltage high alarm
+in[1-6]_min		Minimum output voltage
+in[1-6]_min_alarm	Output voltage low alarm
+
+temp[1-11]_crit		Critical high temperature
+temp[1-11]_crit_alarm	Chip temperature critical high alarm
+temp[1-11]_input	Measured temperature
+temp[1-11]_max		Maximum temperature
+temp[1-11]_max_alarm	Chip temperature high alarm

drivers/hwmon/pmbus/Kconfig

@@ -114,6 +114,16 @@ config SENSORS_MAX20751
 	  This driver can also be built as a module. If so, the module will
 	  be called max20751.
 
+config SENSORS_MAX31785
+	tristate "Maxim MAX31785 and compatibles"
+	default n
+	help
+	  If you say yes here you get hardware monitoring support for Maxim
+	  MAX31785.
+
+	  This driver can also be built as a module. If so, the module will
+	  be called max31785.
+
 config SENSORS_MAX34440
 	tristate "Maxim MAX34440 and compatibles"
 	default n

drivers/hwmon/pmbus/Makefile

@@ -12,6 +12,7 @@ obj-$(CONFIG_SENSORS_LTC2978)	+= ltc2978.o
 obj-$(CONFIG_SENSORS_LTC3815)	+= ltc3815.o
 obj-$(CONFIG_SENSORS_MAX16064)	+= max16064.o
 obj-$(CONFIG_SENSORS_MAX20751)	+= max20751.o
+obj-$(CONFIG_SENSORS_MAX31785)	+= max31785.o
 obj-$(CONFIG_SENSORS_MAX34440)	+= max34440.o
 obj-$(CONFIG_SENSORS_MAX8688)	+= max8688.o
 obj-$(CONFIG_SENSORS_TPS40422)	+= tps40422.o

drivers/hwmon/pmbus/max31785.c

@@ -0,0 +1,116 @@
+/*
+ * Copyright (C) 2017 IBM Corp.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include "pmbus.h"
+
+enum max31785_regs {
+	MFR_REVISION		= 0x9b,
+};
+
+#define MAX31785_NR_PAGES		23
+
+#define MAX31785_FAN_FUNCS \
+	(PMBUS_HAVE_FAN12 | PMBUS_HAVE_STATUS_FAN12)
+
+#define MAX31785_TEMP_FUNCS \
+	(PMBUS_HAVE_TEMP | PMBUS_HAVE_STATUS_TEMP)
+
+#define MAX31785_VOUT_FUNCS \
+	(PMBUS_HAVE_VOUT | PMBUS_HAVE_STATUS_VOUT)
+
+static const struct pmbus_driver_info max31785_info = {
+	.pages = MAX31785_NR_PAGES,
+
+	/* RPM */
+	.format[PSC_FAN] = direct,
+	.m[PSC_FAN] = 1,
+	.b[PSC_FAN] = 0,
+	.R[PSC_FAN] = 0,
+	.func[0] = MAX31785_FAN_FUNCS,
+	.func[1] = MAX31785_FAN_FUNCS,
+	.func[2] = MAX31785_FAN_FUNCS,
+	.func[3] = MAX31785_FAN_FUNCS,
+	.func[4] = MAX31785_FAN_FUNCS,
+	.func[5] = MAX31785_FAN_FUNCS,
+
+	.format[PSC_TEMPERATURE] = direct,
+	.m[PSC_TEMPERATURE] = 1,
+	.b[PSC_TEMPERATURE] = 0,
+	.R[PSC_TEMPERATURE] = 2,
+	.func[6]  = MAX31785_TEMP_FUNCS,
+	.func[7]  = MAX31785_TEMP_FUNCS,
+	.func[8]  = MAX31785_TEMP_FUNCS,
+	.func[9]  = MAX31785_TEMP_FUNCS,
+	.func[10] = MAX31785_TEMP_FUNCS,
+	.func[11] = MAX31785_TEMP_FUNCS,
+	.func[12] = MAX31785_TEMP_FUNCS,
+	.func[13] = MAX31785_TEMP_FUNCS,
+	.func[14] = MAX31785_TEMP_FUNCS,
+	.func[15] = MAX31785_TEMP_FUNCS,
+	.func[16] = MAX31785_TEMP_FUNCS,
+
+	.format[PSC_VOLTAGE_OUT] = direct,
+	.m[PSC_VOLTAGE_OUT] = 1,
+	.b[PSC_VOLTAGE_OUT] = 0,
+	.R[PSC_VOLTAGE_OUT] = 0,
+	.func[17] = MAX31785_VOUT_FUNCS,
+	.func[18] = MAX31785_VOUT_FUNCS,
+	.func[19] = MAX31785_VOUT_FUNCS,
+	.func[20] = MAX31785_VOUT_FUNCS,
+	.func[21] = MAX31785_VOUT_FUNCS,
+	.func[22] = MAX31785_VOUT_FUNCS,
+};
+
+static int max31785_probe(struct i2c_client *client,
+			  const struct i2c_device_id *id)
+{
+	struct device *dev = &client->dev;
+	struct pmbus_driver_info *info;
+	s64 ret;
+
+	info = devm_kzalloc(dev, sizeof(struct pmbus_driver_info), GFP_KERNEL);
+	if (!info)
+		return -ENOMEM;
+
+	*info = max31785_info;
+
+	ret = i2c_smbus_write_byte_data(client, PMBUS_PAGE, 255);
+	if (ret < 0)
+		return ret;
+
+	return pmbus_do_probe(client, id, info);
+}
+
+static const struct i2c_device_id max31785_id[] = {
+	{ "max31785", 0 },
+	{ "max31785a", 0 },
+	{ },
+};
+
+MODULE_DEVICE_TABLE(i2c, max31785_id);
+
+static struct i2c_driver max31785_driver = {
+	.driver = {
+		.name = "max31785",
+	},
+	.probe = max31785_probe,
+	.remove = pmbus_do_remove,
+	.id_table = max31785_id,
+};
+
+module_i2c_driver(max31785_driver);
+
+MODULE_AUTHOR("Andrew Jeffery <andrew@aj.id.au>");
+MODULE_DESCRIPTION("PMBus driver for the Maxim MAX31785");
+MODULE_LICENSE("GPL");