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SubjectRe: [PATCH 7/7] hwmon: (core) Document new kernel API
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On 26/06/16 04:26, Guenter Roeck wrote:
> Describe the new registration API function as well as the data
> structures it requires.
>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Nice docs. Couple of typos inline.

Jonathan
> ---
> Documentation/hwmon/hwmon-kernel-api.txt | 229 ++++++++++++++++++++++++++++++-
> 1 file changed, 227 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/hwmon/hwmon-kernel-api.txt b/Documentation/hwmon/hwmon-kernel-api.txt
> index 2ecdbfc85ecf..1a96c36532f2 100644
> --- a/Documentation/hwmon/hwmon-kernel-api.txt
> +++ b/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 priovided if any writeable attributes exist.
provided
> +
> +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 atributes. Only non-standard
attributes
> +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.
>

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