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 11:11:44 +0200
From:	Jean Delvare <khali@...ux-fr.org>
To:	Wei Ni <wni@...dia.com>
Cc:	Guenter Roeck <linux@...ck-us.net>,
	Thierry Reding <thierry.reding@...il.com>, rui.zhang@...el.com,
	lm-sensors@...sensors.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH v3 1/4] hwmon: (lm90) split set&show temp as common
 codes

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 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.

-- 
Jean Delvare
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