Re: [PATCH] iio: potentiometer: add driver for Maxim Integrated DS1807

[Jonathan Cameron <jic23@kernel.org>]

On Sat, 23 Feb 2019 10:04:31 +0100
Michael Nazzareno Trimarchi <michael@amarulasolutions.com> wrote:

> Hi Jonathan
> 
> Very old thread. I have created Giotto Tune based on this design and
> now try to attach to ds1807. I have done some hack on the current
> interface to have it working in alsa. I have some trouble with the API
> 
>   fragment@3 {
>                 target = <&sound>;
>                 __overlay__ {
>                         compatible = "bcm2708,bcm2708-audio-giotto";
>                         i2s-controller = <&i2s>;
>                         io-channels = <&volume 0>;

This is a list, not just one.

>                         #io-channel-cells = <1>;
>                         nreset = <&gpio 5 1>;
>                         status = "okay";
>                 };
>         };
> 
>         fragment@4 {
>                 target = <&spidev0>;
>                 __overlay__ {
>                         status = "disabled";
>                 };
>         };
> 
>         fragment@5 {
>                 target = <&i2c1>;
>                 __overlay__ {
>                         #address-cells = <1>;
>                         #size-cells = <0>;
>                         status = "okay";
> 
>                         volume: ds1807@1 {
>                                 compatible = "maxim,ds1807";
>                                 reg = <0x28>;
>                                 status = "okay";
>                                 #io-channel-cells = <1>;
>                         };
>                 };
>         };
> 
> This is the overlay and this is the change of the API
> 
> -static int iio_channel_write(struct iio_channel *chan, int val, int val2,
> +static int iio_channel_write(struct iio_channel *chan, int index, int
> val, int val2,
>                              enum iio_chan_info_enum info)
>  {
>         return chan->indio_dev->info->write_raw(chan->indio_dev,
> -                                               chan->channel, val, val2, info);
> +                                               &chan->channel[index],
> val, val2, info);
>  }
> 
> +int iio_write_channel_attribute(struct iio_channel *chan, int index,
> int val, int val2,
> +                                enum iio_chan_info_enum attribute)
> +{
> +       int ret;
> +
> +       mutex_lock(&chan->indio_dev->info_exist_lock);
> +       if (chan->indio_dev->info == NULL) {
> +               ret = -ENODEV;
> +               goto err_unlock;
> +       }
> +
> +       if (index < 0 || index > chan->indio_dev->num_channels)
> +               return -EINVAL;
> +
> +       ret = iio_channel_write(chan, index, val, val2, attribute);
> +err_unlock:
> +       mutex_unlock(&chan->indio_dev->info_exist_lock);
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(iio_write_channel_attribute);
> 
> I order to trigger both controls
> 
> +       ret = iio_write_channel_attribute(&data->iio_ch[0], 0,
> +                                         val, 0,
> +                                         IIO_CHAN_INFO_HARDWAREGAIN);
> +       if (ret < 0)
> +                return ret;
> +
> +       ret = iio_write_channel_attribute(&data->iio_ch[0], 1,
> +                                         val, 0,
> +                                         IIO_CHAN_INFO_HARDWAREGAIN);
> +       if (ret < 0)
> +                return ret;
> +
> 
> The problem is that we can have one iio_dev and multiple raw value for
> each one. 

Absolutely we can, but you need to register multiple channels and get them
all, not just one and then try and build off that.

> Is this the correct way?

No.  You need to have multiple channels listed, not just the one.

There are examples in Documentation/bindings/iio/iio-bindings.txt

I may be misunderstanding what you are trying to do.

Jonathan


> 
> Michael
> 
> On Sat, May 12, 2018 at 2:10 PM Michael Nazzareno Trimarchi
> <michael@amarulasolutions.com> wrote:
> >
> > Hi
> >
> > On Sat, May 12, 2018 at 1:07 PM, Jonathan Cameron <jic23@kernel.org> wrote:  
> > > On Sat, 12 May 2018 11:50:23 +0200
> > > Michael Nazzareno Trimarchi <michael@amarulasolutions.com> wrote:
> > >  
> > >> Hi
> > >>
> > >> On Sat, May 12, 2018 at 11:45 AM, Jonathan Cameron <jic23@kernel.org> wrote:  
> > >> > On Wed, 9 May 2018 11:19:51 +0200
> > >> > Michael Nazzareno Trimarchi <michael@amarulasolutions.com> wrote:
> > >> >  
> > >> >> Hi Jonathan
> > >> >>
> > >> >>
> > >> >> On Wed, May 9, 2018 at 11:01 AM, Michael Nazzareno Trimarchi
> > >> >> <michael@amarulasolutions.com> wrote:  
> > >> >> > Hi
> > >> >> >
> > >> >> > On Mon, May 7, 2018 at 7:17 PM, Jonathan Cameron <jic23@kernel.org> wrote:  
> > >> >> >> On Mon, 7 May 2018 18:55:16 +0200
> > >> >> >> Lars-Peter Clausen <lars@metafoo.de> 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@amarulasolutions.com> 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!)  
> >
> > Yes it's a good idea. I will try but I need to move my development
> > board on latest
> > kernel.
> >
> > Michael
> >  
> > >
> > > 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               |  
> > >> >>
> > >> >>
> > >> >>  
> > >> >  
> > >>
> > >>
> > >>  
> > >  
> >
> >
> >
> > --
> > | Michael Nazzareno Trimarchi                     Amarula Solutions BV |
> > | COO  -  Founder                                      Cruquiuskade 47 |
> > | +31(0)851119172                                 Amsterdam 1018 AM NL |
> > |                  [`as] http://www.amarulasolutions.com               |  
> 
> 
>