linux-kernel - Re: [PATCH v3 1/4] hwmon: (lm90) split set&show temp as common codes

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Date:	Wed, 17 Jul 2013 17:54:54 +0800
From:	Wei Ni <wni@...dia.com>
To:	Jean Delvare <khali@...ux-fr.org>
CC:	Guenter Roeck <linux@...ck-us.net>,
	Thierry Reding <thierry.reding@...il.com>,
	"rui.zhang@...el.com" <rui.zhang@...el.com>,
	"lm-sensors@...sensors.org" <lm-sensors@...sensors.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v3 1/4] hwmon: (lm90) split set&show temp as common codes

On 07/17/2013 05:11 PM, Jean Delvare wrote:
> On Wed, 17 Jul 2013 14:26:54 +0800, Wei Ni wrote:
>> On 07/17/2013 01:14 PM, Guenter Roeck wrote:
>>> On Wed, Jul 17, 2013 at 06:26:20AM +0200, Thierry Reding wrote:
>>>> On Mon, Jul 15, 2013 at 09:24:15AM +0200, Jean Delvare wrote:
>>>>> On Mon, 15 Jul 2013 14:25:29 +0800, Wei Ni wrote:
>>>>>> I think we can decide it in the DT, we can add a dt property in the lm90
>>>>>> device node, such as:
>>>>>> sys-interface = SYS_HWMON;
>>>>>> or
>>>>>> sys-interface = SYS_THERMAL;
>>>>>> So we register it as the hwmon or thermal device
>>>>>
>>>>> This is an option, but please keep in mind that DT is not the only way
>>>>> to instantiate LM90-like devices, and we should not expose duplicate
>>>>> inputs by default. It is fine with me if the default is to create only a
>>>>> HWMON device (as the lm90 driver was doing so far), and only
>>>>> DT-instantiated devices have the choice.
>>>>
>>>> I don't think this information belongs in the device tree. Whether the
>>>> device is exposed as hwmon or thermal device (or both) is entirely a
>>>> software issue whereas DT is a means to describe the hardware.
>>>>
>>> Correct; this is exactly the type of information which does _not_ belong int
>>> devicetree.
>>>
>>>> It seems to me that the earlier proposal of communicating to the bridge
>>>> whether or not a device should be exposed as hwmon device is the right
>>>> thing to do here.
>>>
>>> Agreed..
>>
>> Sorry, what's the "bridge" mean,
> 
> The code which creates a virtual hwmon input when a new thermal zone is
> registered (this code is in thermal_core.c.)
> 
>> does it mean we need to add a flag in
>> the thermal_zone_device_register() to indicate if we want to register
>> virtual hwmon device or not?
> 
> I think so, yes.
> 
> Alternatively the flag could be added to struct
> thermal_zone_device_ops, so that you don't have to update all the
> callers. But I admit it's a hack as the flag doesn't really belong
> there, so I suppose we don't really want to do that.

I think it's better to add it to struct thermal_zone_params, the
thermal_zone_device_ops is for the callback functions.
And I ask it with thermal fw engineers in
http://thread.gmane.org/gmane.linux.power-management.general/35874.
May be you can look it.

> 
> I have been thinking of an automatic approach, based on comparing the
> type string passed to thermal_zone_device_register() with already
> registered hwmon devices, but I couldn't come up with something good
> and robust enough, so let's forget about it.
> 

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