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hwmon: (core) Document new kernel API

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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>
This commit is contained in:
Guenter Roeck 2016-06-23 18:57:03 -07:00
parent 8faee73f92
commit bf7153fd2c
1 changed files with 227 additions and 2 deletions
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229
Documentation/hwmon/hwmon-kernel-api.txt
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@ -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.