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. -- 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
