Re: [PATCH] iio: potentiometer: add driver for Maxim Integrated DS1807

[Michael Nazzareno Trimarchi <michael@amarulasolutions.com>]

Hi

On Mon, May 7, 2018 at 7:17 PM, Jonathan Cameron <jic23@kernel.org> wrote:
> On Mon, 7 May 2018 18:55:16 +0200
> Lars-Peter Clausen <lars@metafoo.de> wrote:
>
>> On 05/07/2018 06:44 PM, Lars-Peter Clausen wrote:
>> > On 05/06/2018 07:37 PM, Jonathan Cameron wrote:
>> >> On Sun,  6 May 2018 15:30:47 +0200
>> >> Michael Trimarchi <michael@amarulasolutions.com> wrote:
>> >>
>> >>> The following functions are supported:
>> >>> - write, read potentiometer value
>> >>>
>> >>> Value are exported in DBm because it's used as an audio
>> >>> attenuator
>> >>
>> >> This is interesting.  The problem is that there is no way for
>> >> userspace to know that it is reporting in DBm rather than
>> >> reporting a linear gain or a straight forward resistance.
>> >>
>> >> This is rather closer in operation to the analog front end
>> >> driver I took the other day than to the other potentiometers
>> >> we have drivers for.
>> >>
>> >> Anyhow, how to solve this?  Two options come to mind.
>> >> 1) Look up table mapping to linear gain as per current ABI
>> >> 2) Add a new channel type to represent the fact we are
>> >> looking at a logarithmic value, letting us handle it as DB.
>> >
>> > Yeah, I guess it is a bit difficult. I don't think this should be a separate
>> > type since we are still describing the same thing, just the scale is
>> > logarithmic rather than linear. Translation table doesn't work either since
>> > your values would get ridiculous small/large. We could add a db suffix to
>> > the type, but that's just terrible. I guess the best we can do is have a
>> > scale attribute that says 1dB.
>>
>> The other problem of course is that dB is a relative unit. The ratio of one
>> value to another. Whereas our normal scale refers to an absolute value.
> I'm really not keen on this.  We have done the separate types
> for humidity already, where we had relative (which is a ratio) and absolute
> (which isn't).  It's not pretty though.
>
> Potentially we could define a new attribute that says this one is
> is db or linear but that's ugly too.
>
> As you asked, are we looking at a part that gets used for anything other
> than audio or not?  If just audio, alsa driver does indeed make more sense.
>

This can be used in audio but even in other field. It's just a potentiometer.
Can I know what is wrong to use the same approch of audio ampliefier that we
have already in the iio tree?

Michael

> Jonathan



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| Michael Nazzareno Trimarchi                     Amarula Solutions BV |
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