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 06:26:20 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Jean Delvare <khali@...ux-fr.org>
Cc:	Wei Ni <wni@...dia.com>, Guenter Roeck <linux@...ck-us.net>,
	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 Mon, Jul 15, 2013 at 09:24:15AM +0200, Jean Delvare wrote:
> On Mon, 15 Jul 2013 14:25:29 +0800, Wei Ni wrote:
> > On 07/12/2013 10:40 PM, Guenter Roeck wrote:
> > > On Fri, Jul 12, 2013 at 04:30:34PM +0200, Jean Delvare wrote:
> > >> If that means that for example the ACPI thermal zone is no longer
> > >> displayed by "sensors", then I strongly object - unless it is
> > >> explicitly registered as a separate hwmon device from now on, of course.
> > >
> > > If I recall correctly that was the idea. Of course, in practice that will mean
> > > that devices will _not_ get exposed as hwmon devices, as implementers won't
> > > bother doing both.
> > > 
> > >> My idea was to make the bridge optional - you decide when you register
> > >> a thermal device if it should be exposed as hwmon or not.
> > >
> > > Yes, that would be a much better solution.
> > 
> > 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.

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.

Thierry

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