linux-kernel - Re: [PATCH 3/4] hwmon: Add a simple driver to read the MXS SoC temperature

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Date:	Fri, 28 Jun 2013 17:24:43 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
CC:	Guenter Roeck <linux@...ck-us.net>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Shawn Guo <shawn.guo@...aro.org>,
	Jean Delvare <khali@...ux-fr.org>, jimwall@...om,
	brian@...stalfontz.com, Grant Likely <grant.likely@...aro.org>,
	Rob Herring <rob.herring@...xeda.com>,
	Rob Landley <rob@...dley.net>,
	Russell King <linux@....linux.org.uk>,
	devicetree-discuss@...ts.ozlabs.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, lm-sensors@...sensors.org,
	linux-arm-kernel@...ts.infradead.org, linux-iio@...r.kernel.org
Subject: Re: [PATCH 3/4] hwmon: Add a simple driver to read the MXS SoC temperature

On 06/28/2013 04:50 PM, Alexandre Belloni wrote:
> On 28/06/2013 16:18, Lars-Peter Clausen wrote:
>> On 06/27/2013 09:26 PM, Alexandre Belloni wrote:
>>>
>>> They are already registered as IIO_TEMP but only implement read_raw. Also,
>>>
>>> iio_hwmon_read_val() is using iio_read_channel_processed() and that will
>>> basically only read one of the 2 channels. As I documented, you actually
>>> need to read both channel 8 and channel 9 and then compute the value in
>>> Kelvins. I'm not sure how you want me to do that in the current framework.
>> What are these two channels actually measuring? Is the value of a single
>> channel meaningful on it's own? If not it might make sense to update the IIO
>> driver to just have one temperature channel.
> 
> It's not actually meaningful on its own. So, what you would do is expose
> one iio channel for two ADC channels and do the computation in read_raw
> ? or read_processed ? Then using iio-hwon to export it. ?
> 
> Regards,
> 

Yes, return channel9 - channel8 as the raw value for the temperature channel
and provide proper scale and offset values, so that
iio_read_channel_processed() will return the correct value.

- Lars
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