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

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Date:	Tue, 30 Dec 2014 19:00:02 +0100
From:	Pavel Machek <pavel@....cz>
To:	Nishanth Menon <nm@...com>
Cc:	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>,
	Guenter Roeck <linux@...ck-us.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/3] hwmon: Driver for OMAP3 temperature sensor

On Mon 2014-12-29 14:35:55, Nishanth Menon wrote:
> On 12/29/2014 12:15 PM, 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.
> 
> Just be careful when you try to make thermal policy like decisions
> based on this sensor. Placement of the sensor w.r.t the actual logic

I guess we won't do that, certainly not anytime soon.

> Also notice http://www.ti.com/lit/er/sprz278f/sprz278f.pdf "Advisory
> 3.1.1.186 MMC OCP Clock Not Gated When Thermal Sensor Is Used" I think
> there were accuracy issues at certain values etc.. So remember to do a
> off mode type PM tests as well before you consider requesting these to
> be merged.

Thanks a lot for a pointer. 3x 100uA power draw when you enable
temperature sensor, because it also errorneously enables MMC. I wonder
how the solution would look in the device tree...
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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