Hi On Sat, May 12, 2018 at 11:45 AM, Jonathan Cameron <jic23@xxxxxxxxxx> wrote: > On Wed, 9 May 2018 11:19:51 +0200 > Michael Nazzareno Trimarchi <michael@xxxxxxxxxxxxxxxxxxxx> wrote: > >> 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 > > Wow, somehow that entire thing had slipped my mind. I guess we went > through the whole question of how to support dB scales years ago > and it has just been very little used. > > Hmm. Sorry for my absent mindedness! Anyhow, there are a few additional > comments that need cleaning up. > > It is going to be a little odd as the only potentiometer (I think) that > is acting as a scale free attenuator, rather that being controlled on the basis > of resistance, but for the part that seems to make sense so fair enough. > > I'm slightly curious to know what you have this wired up to though? I'm design GIOTTO ;) an audio module that use those to control the volume. It's a dsd native sound card that demultiplex i2s to L and R dsd on a pcm1795a. Everything already run under linux. The idea is to create an audio card and connect iio device to the volume to change dsd volume > Are the inputs and outputs invisible to the kernel or is this feeding > into another device? I think a reply above. Anyway we don't want to have driver duplication and I think should be land there > > If we are feeding another device then the work recently done on a > generic AFE driver may be useful. At somepoint we'll need a version Can you point to it? I need to read about ;) Michael > of that which deals with standalone amplifiers and attenuators anyway, > but I don't know if it is useful to you. > > Jonathan > > Jonathan > > >> >> 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
