Hi Jonathan On Wed, May 9, 2018 at 11:01 AM, Michael Nazzareno Trimarchi <michael@xxxxxxxxxxxxxxxxxxxx> wrote: > 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? > cat /sys/bus/iio/devices/iio:device1/out_altvoltage0_hardwaregain -10.000000 dB echo -10 > /sys/bus/iio/devices/iio:device1/out_altvoltage0_hardwaregain uname -a Linux linaro-alip 4.4.93 #7 SMP Sun May 6 13:23:08 CEST 2018 armv7l GNU/Linux Michael > Michael > >> Jonathan > > > > -- > | Michael Nazzareno Trimarchi Amarula Solutions BV | > | COO - Founder Cruquiuskade 47 | > | +31(0)851119172 Amsterdam 1018 AM NL | > | [`as] http://www.amarulasolutions.com | -- | 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
