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

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Date:	Mon, 29 Dec 2014 14:35:55 -0600
From:	Nishanth Menon <nm@...com>
To:	Pavel Machek <pavel@....cz>
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 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
generating heat has to be a factor as well. If you are just looking
for an approximation temperature (thermometerish kind), you might be
ok with this. I am not sure we'd find any TI data around this.. just a
heads up.

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.

-- 
Regards,
Nishanth Menon
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