linux-kernel - Re: [PATCH v2 1/2] iio: core: introduce IIO_CHAN_INFO

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Message-ID: <56E08FD5.4060701@kernel.org>
Date:	Wed, 9 Mar 2016 21:04:21 +0000
From:	Jonathan Cameron <jic23@...nel.org>
To:	Lars-Peter Clausen <lars@...afoo.de>,
	Ludovic Desroches <ludovic.desroches@...el.com>
Cc:	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, nicolas.ferre@...el.com
Subject: Re: [PATCH v2 1/2] iio: core: introduce IIO_CHAN_INFO_SIGNED

On 07/03/16 20:09, Lars-Peter Clausen wrote:
> On 03/07/2016 03:29 PM, Ludovic Desroches wrote:
>> The same channel can be used to perform a signed or an unsigned
>> conversion. Add a new infomask element to be able to select the type of
>> conversion wanted: a raw one or a signed raw one.
> 
> If this is the difference between offset binary and two's complement then it
> makes no sense to expose this at this level. Both are the same number just
> in a different representation and converting between them is cheap. A few
> magnitudes cheaper than reading the result over sysfs. So, if your device
> supports both, just pick one.
> 
> For the buffered interface it may make sense to expose this, since the per
> sample overhead is a lot lower. But still doing the conversion should be
> cheap enough that it does not really matter. Before this is implemented I'd
> like to see hard performance numbers that this actually makes a difference.
> 
> - Lars
> 
Definitely looking for more detail on this.  I'd missed we were talking simply
about representation (which is also how I read 62.6.6 Conversion Results Format
in the datasheet). Not entirely sure what I imagined the difference between
signed and unsigned output would be!

Jonathan