linux-kernel - Re: [PATCH v2 5/5] iio: mxs-lradc: add write

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Message-ID: <51E967D8.8020001@digi.com>
Date:	Fri, 19 Jul 2013 18:22:48 +0200
From:	Hector Palacios <hector.palacios@...i.com>
To:	Marek Vasut <marex@...x.de>
CC:	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"alexandre.belloni@...e-electrons.com" 
	<alexandre.belloni@...e-electrons.com>,
	"jic23@...nel.org" <jic23@...nel.org>,
	"lars@...afoo.de" <lars@...afoo.de>,
	"fabio.estevam@...escale.com" <fabio.estevam@...escale.com>
Subject: Re: [PATCH v2 5/5] iio: mxs-lradc: add write_raw function to modify
 scale

Dear Marek,

On 07/19/2013 06:17 PM, Marek Vasut wrote:
>> Here you have three entries per channel:
>> in_voltageX_raw		-> the sample raw value
>> in_voltageX_scale	-> the scale to multiply the raw value to get the
> voltage
>> in mV in_voltageX_scale_available -> lists the available scales of the
>> channel
>>
>> For example for channel 0:
>>
>> # cat in_voltage0_scale_available
>> 0.451660156 0.903320312	(two scales available, first with divider by two
>> disabled, second with divider by two enabled)
>>
>> # cat in_voltage0_scale
>> 0.451660156			(divider by two is currently disabled)
>>
>> # cat in_voltage0_raw		(shows measured value)
>> 1000
>>
>> If you multiply the value by the scale you get: 1000 * 0.451660156 = 451.6
>> mV
>>
>> # echo 0.903320312 > in_voltage0_scale	(enables the divider by two)
>
> Ok, so I have to remember this value : '0.903320312' in case I want to enable
> divide-by-two functionality?

No you don't. That's why there is a 'in_voltage_scale_available' that lists the 
available values.

> Hmmmm ... why would this interface not work:
> echo 2 > in_voltage0_scale
>
> or
>
> echo 1 > in_voltage0_scale

An easy thing like that is what I first submitted, but it was rejected and I was told 
to use the scale_available descriptor instead, which is the common interface the rest 
of drivers use.

Best regards,
--
Hector Palacios
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