On Sat, 12 May 2018 11:50:23 +0200 Michael Nazzareno Trimarchi <michael@xxxxxxxxxxxxxxxxxxxx> wrote: > 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 ;) https://patchwork.kernel.org/patch/10358131/ Should be in linux-next by now ready for the next merge window. As it turns out, probably not relevant in your case you will probably want to have the sound card as a consumer so that the volume control maps nicely via usual interface etc. Perhaps cc the relevant sound lists and maintainers on next version. I don't want to tread on anyone's toes if they are of the view that it shouldn't be done this way (should be fine from previous conversations with a few of them!) Jonathan > > 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 | > >> > >> > >> > > > > > -- 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
