linux-kernel - Re: [RFC PATCH 0/2] HWMON: add in-kernel interfaces to read sensor values.

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Date:	Mon, 14 Nov 2011 16:39:42 +0000
From:	Jonathan Cameron <jic23@....ac.uk>
To:	myungjoo.ham@...il.com
CC:	MyungJoo Ham <myungjoo.ham@...sung.com>,
	Ben Hutchings <bhutchings@...arflare.com>,
	lm-sensors@...sensors.org, linux-kernel@...r.kernel.org,
	Jean Delvare <khali@...ux-fr.org>,
	Guenter Roeck <guenter.roeck@...csson.com>,
	dg77.kim@...sung.com, kyungmin.park@...sung.com
Subject: Re: [RFC PATCH 0/2] HWMON: add in-kernel interfaces to read sensor
 values.

On 11/14/2011 01:31 AM, MyungJoo Ham wrote:
> On Sat, Nov 12, 2011 at 5:46 AM, Ben Hutchings
> <bhutchings@...arflare.com> wrote:
>> On Fri, 2011-11-04 at 15:50 +0900, MyungJoo Ham wrote:
>>> We have been reading hwmon values (TMU, the SoC-core temperature sensor,
>>> and NTC, the ambient or battery surface temperature sensor) for
>>> Charger-Manager. However, because hwmon does not have in-kernel interface,
>>> we have been using undesired method, including "../../../fs/*.h".
>>>
>>> This patch is to provide in-kernel interface for hwmon:
>>> hwmon_get_value and hwmon_set_value. In order to use these two functions,
>>> the hwmon driver should provide its sysfs attributes to hwmon framework
>>> as well. If the hwmon driver does not provide (by providing NULL), the users
>>> of the hwmon won't be able to use hwmon_get/set_value();
>>> The sysfs attribute (struct attribuyte_group *) is provided with
>>> hwmon_device_register; adding the second parameter to hwmon_device_register().
>>> The 2/2 patch shows the changes in device drivers due to this.
>> [...]
>>
>> This is an improvement, but I don't think it is quite enough.  As I
>> understand the hwmon sysfs interface, all sensor values should be
>> integers.  So the in-kernel interface should also work with integers,
>> not strings.
>>
>> As a first implementation you could perhaps parse the strings back to
>> integers.  However in the longer term the driver API should be changed
>> so that hwmon drivers fully describe their sensors to the core and the
>> core takes care of exposing them through sysfs and the in-kernel API.
> 
> I agree.
> 
> I'll let it the in-kernel interfaces provide integer value although it will
> simply parse strings as you've addressed until we have some other
> interfaces for sysfs entries in hwmon device drivers.
> 
> 
To throw another option into the mix, you could make it an IIO driver
and sit hwmon on top of that (there is already a simple driver for
doing this) - IIO has in kernel interfaces of the type
you want.  Not everything is there yet though.

Jonathan

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