linux-kernel - Re: [PATCH v3 2/3] iio:adc:palmas: add DT support

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Date:	Mon, 19 Oct 2015 14:30:33 +0200
From:	"H. Nikolaus Schaller" <hns@...delico.com>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Benoît Cousson <bcousson@...libre.com>,
	Tony Lindgren <tony@...mide.com>,
	Russell King <linux@....linux.org.uk>,
	Marek Belisko <marek@...delico.com>,
	Pradeep Goudagunta <pgoudagunta@...dia.com>,
	Laxman Dewangan <ldewangan@...dia.com>,
	Graeme Gregory <gg@...mlogic.co.uk>,
	jic23@...23.retrosnub.co.uk, devicetree@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	linux-omap <linux-omap@...r.kernel.org>,
	linux-iio@...r.kernel.org, Grazvydas Ignotas <notasas@...il.com>,
	Lee Jones <lee.jones@...aro.org>,
	Samuel Ortiz <sameo@...ux.intel.com>
Subject: Re: [PATCH v3 2/3] iio:adc:palmas: add DT support


Am 19.10.2015 um 13:57 schrieb Lars-Peter Clausen <lars@...afoo.de>:

> On 10/16/2015 02:53 PM, H. Nikolaus Schaller wrote:
> [...]
>> +Optional sub-nodes:
>> +ti,channel0-current-microamp: Channel 0 current in uA.
>> +	Values are rounded to derive 0uA, 5uA, 15uA, 20uA.
>> +ti,channel3-current-microamp: Channel 3 current in uA.
>> +	Valid are rounded to derive 0uA, 10uA, 400uA, 800uA.
>> +ti,enable-extended-delay: Enable extended delay.
> 
> Those three above sound more like configuration policy, rather than hardware
> description. What influence which values should be chosen?

e.g. the nominal value of the NTC that can be connected if the Palmas
is hooked up in a standard way.

If a board has no NTC and uses channel0 for a different purpose one
should choose 0uA.

If it is let's say 10kOhm it should probably be 20uA to give a nominal voltage
reading of 200mV.

100kOhm will give 2V which is at the limit of the ADC input range and
therefore it would be better to choose 15uA or 5uA.

I think choosing extended delay depends on the noisiness of the input
signal but I am not a specialist for this feature.

So I would say the board hardware mandates some specific value.

BR,
Nikolaus

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