hwmon: (core) Document new kernel API

Describe the new registration API function as well as the data
structures it requires.
Acked-by: Punit Agrawal <punit.agrawal@arm.com>
Reviewed-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/hwmon-kernel-api.txt

@@ -34,6 +34,19 @@ devm_hwmon_device_register_with_groups(struct device *dev,
 				       const char *name, void *drvdata,
 				       const struct attribute_group **groups);
 
+struct device *
+hwmon_device_register_with_info(struct device *dev,
+				const char *name, void *drvdata,
+				const struct hwmon_chip_info *info,
+				const struct attribute_group **groups);
+
+struct device *
+devm_hwmon_device_register_with_info(struct device *dev,
+				     const char *name,
+				     void *drvdata,
+				     const struct hwmon_chip_info *info,
+				     const struct attribute_group **groups);
+
 void hwmon_device_unregister(struct device *dev);
 void devm_hwmon_device_unregister(struct device *dev);
 
@@ -60,15 +73,227 @@ devm_hwmon_device_register_with_groups is similar to
 hwmon_device_register_with_groups. However, it is device managed, meaning the
 hwmon device does not have to be removed explicitly by the removal function.
 
+hwmon_device_register_with_info is the most comprehensive and preferred means
+to register a hardware monitoring device. It creates the standard sysfs
+attributes in the hardware monitoring core, letting the driver focus on reading
+from and writing to the chip instead of having to bother with sysfs attributes.
+Its parameters are described in more detail below.
+
+devm_hwmon_device_register_with_info is similar to
+hwmon_device_register_with_info. However, it is device managed, meaning the
+hwmon device does not have to be removed explicitly by the removal function.
+
 hwmon_device_unregister deregisters a registered hardware monitoring device.
 The parameter of this function is the pointer to the registered hardware
 monitoring device structure. This function must be called from the driver
 remove function if the hardware monitoring device was registered with
-hwmon_device_register or with hwmon_device_register_with_groups.
+hwmon_device_register, hwmon_device_register_with_groups, or
+hwmon_device_register_with_info.
 
 devm_hwmon_device_unregister does not normally have to be called. It is only
 needed for error handling, and only needed if the driver probe fails after
-the call to devm_hwmon_device_register_with_groups.
+the call to devm_hwmon_device_register_with_groups and if the automatic
+(device managed) removal would be too late.
+
+Using devm_hwmon_device_register_with_info()
+--------------------------------------------
+
+hwmon_device_register_with_info() registers a hardware monitoring device.
+The parameters to this function are
+
+struct device *dev	Pointer to parent device
+const char *name	Device name
+void *drvdata		Driver private data
+const struct hwmon_chip_info *info
+			Pointer to chip description.
+const struct attribute_group **groups
+			Null-terminated list of additional sysfs attribute
+			groups.
+
+This function returns a pointer to the created hardware monitoring device
+on success and a negative error code for failure.
+
+The hwmon_chip_info structure looks as follows.
+
+struct hwmon_chip_info {
+	const struct hwmon_ops *ops;
+	const struct hwmon_channel_info **info;
+};
+
+It contains the following fields:
+
+* ops:	Pointer to device operations.
+* info: NULL-terminated list of device channel descriptors.
+
+The list of hwmon operations is defined as:
+
+struct hwmon_ops {
+	umode_t (*is_visible)(const void *, enum hwmon_sensor_types type,
+			      u32 attr, int);
+	int (*read)(struct device *, enum hwmon_sensor_types type,
+		    u32 attr, int, long *);
+	int (*write)(struct device *, enum hwmon_sensor_types type,
+		     u32 attr, int, long);
+};
+
+It defines the following operations.
+
+* is_visible: Pointer to a function to return the file mode for each supported
+  attribute. This function is mandatory.
+
+* read: Pointer to a function for reading a value from the chip. This function
+  is optional, but must be provided if any readable attributes exist.
+
+* write: Pointer to a function for writing a value to the chip. This function is
+  optional, but must be provided if any writeable attributes exist.
+
+Each sensor channel is described with struct hwmon_channel_info, which is
+defined as follows.
+
+struct hwmon_channel_info {
+	enum hwmon_sensor_types type;
+	u32 *config;
+};
+
+It contains following fields:
+
+* type: The hardware monitoring sensor type.
+  Supported sensor types are
+  * hwmon_chip		A virtual sensor type, used to describe attributes
+			which apply to the entire chip.
+  * hwmon_temp		Temperature sensor
+  * hwmon_in		Voltage sensor
+  * hwmon_curr		Current sensor
+  * hwmon_power		Power sensor
+  * hwmon_energy	Energy sensor
+  * hwmon_humidity	Humidity sensor
+  * hwmon_fan		Fan speed sensor
+
+* config: Pointer to a 0-terminated list of configuration values for each
+  sensor of the given type. Each value is a combination of bit values
+  describing the attributes supposed by a single sensor.
+
+As an example, here is the complete description file for a LM75 compatible
+sensor chip. The chip has a single temperature sensor. The driver wants to
+register with the thermal subsystem (HWMON_C_REGISTER_TZ), and it supports
+the update_interval attribute (HWMON_C_UPDATE_INTERVAL). The chip supports
+reading the temperature (HWMON_T_INPUT), it has a maximum temperature
+register (HWMON_T_MAX) as well as a maximum temperature hysteresis register
+(HWMON_T_MAX_HYST).
+
+static const u32 lm75_chip_config[] = {
+	HWMON_C_REGISTER_TZ | HWMON_C_UPDATE_INTERVAL,
+	0
+};
+
+static const struct hwmon_channel_info lm75_chip = {
+	.type = hwmon_chip,
+	.config = lm75_chip_config,
+};
+
+static const u32 lm75_temp_config[] = {
+	HWMON_T_INPUT | HWMON_T_MAX | HWMON_T_MAX_HYST,
+	0
+};
+
+static const struct hwmon_channel_info lm75_temp = {
+	.type = hwmon_temp,
+	.config = lm75_temp_config,
+};
+
+static const struct hwmon_channel_info *lm75_info[] = {
+	&lm75_chip,
+	&lm75_temp,
+	NULL
+};
+
+static const struct hwmon_ops lm75_hwmon_ops = {
+	.is_visible = lm75_is_visible,
+	.read = lm75_read,
+	.write = lm75_write,
+};
+
+static const struct hwmon_chip_info lm75_chip_info = {
+	.ops = &lm75_hwmon_ops,
+	.info = lm75_info,
+};
+
+A complete list of bit values indicating individual attribute support
+is defined in include/linux/hwmon.h. Definition prefixes are as follows.
+
+HWMON_C_xxxx	Chip attributes, for use with hwmon_chip.
+HWMON_T_xxxx	Temperature attributes, for use with hwmon_temp.
+HWMON_I_xxxx	Voltage attributes, for use with hwmon_in.
+HWMON_C_xxxx	Current attributes, for use with hwmon_curr.
+		Notice the prefix overlap with chip attributes.
+HWMON_P_xxxx	Power attributes, for use with hwmon_power.
+HWMON_E_xxxx	Energy attributes, for use with hwmon_energy.
+HWMON_H_xxxx	Humidity attributes, for use with hwmon_humidity.
+HWMON_F_xxxx	Fan speed attributes, for use with hwmon_fan.
+
+Driver callback functions
+-------------------------
+
+Each driver provides is_visible, read, and write functions. Parameters
+and return values for those functions are as follows.
+
+umode_t is_visible_func(const void *data, enum hwmon_sensor_types type,
+			u32 attr, int channel)
+
+Parameters:
+	data:	Pointer to device private data structure.
+	type:	The sensor type.
+	attr:	Attribute identifier associated with a specific attribute.
+		For example, the attribute value for HWMON_T_INPUT would be
+		hwmon_temp_input. For complete mappings of bit fields to
+		attribute values please see include/linux/hwmon.h.
+	channel:The sensor channel number.
+
+Return value:
+	The file mode for this attribute. Typically, this will be 0 (the
+	attribute will not be created), S_IRUGO, or 'S_IRUGO | S_IWUSR'.
+
+int read_func(struct device *dev, enum hwmon_sensor_types type,
+	      u32 attr, int channel, long *val)
+
+Parameters:
+	dev:	Pointer to the hardware monitoring device.
+	type:	The sensor type.
+	attr:	Attribute identifier associated with a specific attribute.
+		For example, the attribute value for HWMON_T_INPUT would be
+		hwmon_temp_input. For complete mappings please see
+		include/linux/hwmon.h.
+	channel:The sensor channel number.
+	val:	Pointer to attribute value.
+
+Return value:
+	0 on success, a negative error number otherwise.
+
+int write_func(struct device *dev, enum hwmon_sensor_types type,
+	       u32 attr, int channel, long val)
+
+Parameters:
+	dev:	Pointer to the hardware monitoring device.
+	type:	The sensor type.
+	attr:	Attribute identifier associated with a specific attribute.
+		For example, the attribute value for HWMON_T_INPUT would be
+		hwmon_temp_input. For complete mappings please see
+		include/linux/hwmon.h.
+	channel:The sensor channel number.
+	val:	The value to write to the chip.
+
+Return value:
+	0 on success, a negative error number otherwise.
+
+
+Driver-provided sysfs attributes
+--------------------------------
+
+If the hardware monitoring device is registered with
+hwmon_device_register_with_info or devm_hwmon_device_register_with_info,
+it is most likely not necessary to provide sysfs attributes. Only non-standard
+sysfs attributes need to be provided when one of those registration functions
+is used.
 
 The header file linux/hwmon-sysfs.h provides a number of useful macros to
 declare and use hardware monitoring sysfs attributes.