linux-kernel - Re: [PATCH 2/3] hwmon: Driver for OMAP3 temperature sensor

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Date:	Sun, 18 Jan 2015 21:33:46 +0100
From:	Pavel Machek <pavel@....cz>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Nishanth Menon <nm@...com>, Grazvydas Ignotas <notasas@...il.com>,
	Sebastian Reichel <sre@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	dt list <devicetree@...r.kernel.org>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Tony Lindgren <tony@...mide.com>,
	Kumar Gala <galak@...eaurora.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	lm-sensors@...sensors.org, Rob Herring <robh+dt@...nel.org>,
	Jean Delvare <jdelvare@...e.de>,
	Benoît Cousson <bcousson@...libre.com>,
	Pali Rohar <pali.rohar@...il.com>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/3] hwmon: Driver for OMAP3 temperature sensor

On Wed 2015-01-07 08:19:44, Guenter Roeck wrote:
> On Sat, Jan 03, 2015 at 10:18:58AM +0100, Pavel Machek wrote:
> > On Mon 2014-12-29 11:04:48, Guenter Roeck wrote:
> > > On Mon, Dec 29, 2014 at 07:15:56PM +0100, Pavel Machek wrote:
> > > > On Mon 2014-12-29 12:01:03, Nishanth Menon wrote:
> > > > > On Mon, Dec 29, 2014 at 11:52 AM, Grazvydas Ignotas <notasas@...il.com> wrote:
> > > > > > On Fri, Dec 26, 2014 at 2:34 PM, Sebastian Reichel <sre@...nel.org> wrote:
> > > > > >> OMAP34xx and OMAP36xx processors contain a register in the syscon area,
> > > > > >> which can be used to determine the SoCs temperature. This patch provides
> > > > > >> a DT based driver for the temperature sensor based on an older driver
> > > > > >> written by Peter De Schrijver for the Nokia N900 and N9.
> > > > > >
> > > > > > The sensor looks like an earlier iteration of sensors used in newer
> > > > > > OMAPs, which are already supported by maybe
> > > > > > drivers/thermal/ti-soc-thermal/ , maybe it would make sense to update
> > > > > > that driver instead?
> > > > > 
> > > > > Just to be clear - OMAP4 is the first time that the sensors were
> > > > > reliable enough to be used.
> > > > 
> > > > When testing initial version of the patch, they seem to work very well
> > > > in the omap3 case.
> > > > 
> > > Pavel,
> > > 
> > > can you look into the omap4 thermal driver to see if it can be used ?
> > 
> > After some fixes... yes, it seems to be same hardware.
> > 
> So this should be the way to go, but then we have others claim that
> it should not be done because the OMAP3 sensors are too unreliable
> to use for thermal decisions. Not really sure where that leaves us.
> I am kind of opposed to have similar drivers for similar chips
> in two different subsystems.
> 
> Is it possible to add the patch below to the omap thermal driver
> and not use it for thermal decisions ?

Well... noone forces you to enable the driver, and I don't think it
will do any thermal decisions on N900 as it is ... so we should be ok.

Plus, it seems to work reasonably well (say +- 5 C), so situation does
not seem to be as bad as TI claims.

Nokia was actually using it in production.

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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