Date:	Thu, 15 May 2014 09:58:59 -0700
From:	Randy Dunlap <rdunlap@...radead.org>
To:	Guenter Roeck <linux@...ck-us.net>, Jean Delvare <jdelvare@...e.de>
CC:	lm-sensors@...sensors.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwmon: Document hwmon kernel API

On 05/14/2014 08:02 PM, Guenter Roeck wrote:
> The hwmon subsystem has been around for a while. Time to document
> its kernel API.
> 
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> ---
>  Documentation/hwmon/hwmon-kernel-api.txt | 107 +++++++++++++++++++++++++++++++
>  1 file changed, 107 insertions(+)
>  create mode 100644 Documentation/hwmon/hwmon-kernel-api.txt
> 
> diff --git a/Documentation/hwmon/hwmon-kernel-api.txt b/Documentation/hwmon/hwmon-kernel-api.txt
> new file mode 100644
> index 0000000..70889de
> --- /dev/null
> +++ b/Documentation/hwmon/hwmon-kernel-api.txt
> @@ -0,0 +1,107 @@
> +The Linux Hardware Monitoring kernel API.
> +=========================================
> +
> +Guenter Roeck
> +
> +Introduction
> +------------
> +
> +This document describes the API that can be used by hardware monitoring
> +drivers that want to use the hardware monitoring framework.
> +
> +This document does not describe what a hardware monitoring (hwmon) Driver or
> +Device is. It also does not describe the API which can be used by user space
> +to communicate with a hardware monitoring device. If you want to know this
> +then please read the following file: Documentation/hwmon/sysfs-interface.
> +
> +For additional guidelines on how to write and improve hwmon drivers, please
> +also read Documentation/hwmon/submitting-patches.
> +
> +The API
> +-------
> +Each hardware monitoring driver must #include <linux/hwmon.h> and, in most
> +cases, <linux/hwmon-sysfs.h>. linux/hwmon.h declares the following
> +register/unregister functions:
> +
> +struct device *hwmon_device_register(struct device *dev);
> +struct device *
> +hwmon_device_register_with_groups(struct device *dev, const char *name,
> +				  void *drvdata,
> +				  const struct attribute_group **groups);
> +
> +struct device *
> +devm_hwmon_device_register_with_groups(struct device *dev,
> +				       const char *name, void *drvdata,
> +				       const struct attribute_group **groups);
> +
> +void hwmon_device_unregister(struct device *dev);
> +void devm_hwmon_device_unregister(struct device *dev);
> +
> +hwmon_device_register registers a hardware monitoring device. The parameter
> +of this function is a pointer to the parent device.
> +This function returns a pointer to the newly created hardware monitoring device
> +or PTR_ERR for failure. If this registration function is used, hardware
> +monitoring sysfs attributes are expected to have been created and attached to
> +the parent device prior to calling hwmon_device_register. A name attribute must
> +have been created by the caller.
> +
> +hwmon_device_register_with_groups is similar to hwmon_device_register. However,
> +it has additional parameters. The name parameter is a pointer to the hwmon
> +device name. The registration function wil create a name sysfs attribute
> +pointing to this name. The drvdata parameter is the pointer to the local
> +driver data.  hwmon_device_register_with_groups will attach this pointer
> +to the newly allocated hwmon device. The pointer can be retrieved by the driver
> +using dev_get_drvdata() on the hwmon device pointer. The groups parameter is
> +a pointer to a list of sysfs attribute groups. The list must be NULL terminated.
> +hwmon_device_register_with_groups creates the hwmon device with name attribute
> +as well as all sysfs attributes attached to the hwmon device.
> +
> +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_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.
> +
> +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 include file linux/hwmon-sysfs.h provides a number of useful macros to

       header file

> +declare and use hardware monitoring sysfs attributes.
> +
> +In many cases, you can use the exsting define DEVICE_ATTR to declare such
> +attributes. This is feasible if an attribute has no additional context. However,
> +in many cases there will be additional information such as a sensor index which
> +will need to be passed to the sysfs attribute handling function.
> +
> +SENSOR_DEVICE_ATTR and SENSOR_DEVICE_ATTR_2 can be used to define attributes
> +which need such additional context information. SENSOR_DEVICE_ATTR requires
> +one additional argument, SENSOR_DEVICE_ATTR_2 requires two.
> +
> +SENSOR_DEVICE_ATTR defines a struct sensor_device_attribute variable.
> +This structure has the following fields.
> +
> +struct sensor_device_attribute {
> +	struct device_attribute dev_attr;
> +	int index;
> +};
> +
> +You can use to_sensor_dev_attr to get the pointer to this structure from the
> +attribute read or write function. Parameter is the device to which the attribute

                                     Its parameter is

> +is attached.
> +
> +SENSOR_DEVICE_ATTR_2 defines a struct sensor_device_attribute_2 variable,
> +which is defined as follows.
> +
> +struct sensor_device_attribute_2 {
> +	struct device_attribute dev_attr;
> +	u8 index;
> +	u8 nr;
> +};
> +
> +Use to_sensor_dev_attr_2 to get the pointer to this structure. Parameter is the

                                                                  Its parameter is

> +device to which the attribute is attached.
> 


Acked-by: Randy Dunlap <rdunlap@...radead.org>

Please merge thru the hwmon tree.

thanks,
-- 
~Randy
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