Hi On Mon, May 7, 2018 at 7:17 PM, Jonathan Cameron <jic23@xxxxxxxxxx> wrote: > On Mon, 7 May 2018 18:55:16 +0200 > Lars-Peter Clausen <lars@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxx> 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 -- | Michael Nazzareno Trimarchi Amarula Solutions BV | | COO - Founder Cruquiuskade 47 | | +31(0)851119172 Amsterdam 1018 AM NL | | [`as] http://www.amarulasolutions.com | -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
