Re: [PATCH v5 07/10] dt-bindings: iio: sx9324: Add input analog gain

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 9 May 2022 22:48:26 -0700
Gwendal Grignou <gwendal@chromium.org> wrote:

> On Sun, May 1, 2022 at 10:09 AM Jonathan Cameron <jic23@kernel.org> wrote:
> >
> > On Fri, 29 Apr 2022 15:01:41 -0700
> > Gwendal Grignou <gwendal@chromium.org> wrote:
> >  
> > > Allow setting the configure the input analog gain.
> > >
> > > Signed-off-by: Gwendal Grignou <gwendal@chromium.org>  
> >
> > Hi Gwendal.
> >
> > So, my immediate thought on this is whether it make sense as a
> > dt controlled thing or not. It's the sort of thing hardwaregain
> > is for in the userspace ABI. However, I see that's already
> > in use for the digital gain. This one also unhelpfully applies
> > to all changes whereas the digital gain is pair wise. Hence
> > there is basically no way we can map the two controls to a
> > single ABI element.
> >
> > So, how would we expect a board designer to set this value?
> >
> > If the answer is we basically have no idea but some boards do
> > want it set then I'm fine with this basically being a somewhat magic
> > value that is in some vague way associated with the antenna setup...  
> More or less :-). All these parameters are set with the help of
> Semtech application engineers. The input analog gain is directly
> linked to the antenna design, as it is used by the AFE (Analog Front
> End). The hardwaregain (aka digital gain) comes second during the
> digital processing. We could have put all the settings in the device
> tree, as we don't expect changes once the values are satisfactory to
> pass regulatory testings, but the hybrid approach still allows some
> tinkering: I've use to get a sense of the data amplitude when
> collecting data with /dev/iio:devoceX.

Fair enough. Applied,

Thanks,

Jonathan

> >
> > Jonathan
> >  
> > > ---
> > > New in v5.
> > >
> > >  .../bindings/iio/proximity/semtech,sx9324.yaml        | 11 +++++++++++
> > >  1 file changed, 11 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/iio/proximity/semtech,sx9324.yaml b/Documentation/devicetree/bindings/iio/proximity/semtech,sx9324.yaml
> > > index 0be87ac05b97a..d265eb5258c84 100644
> > > --- a/Documentation/devicetree/bindings/iio/proximity/semtech,sx9324.yaml
> > > +++ b/Documentation/devicetree/bindings/iio/proximity/semtech,sx9324.yaml
> > > @@ -143,6 +143,17 @@ properties:
> > >      description:
> > >        Pre-charge input resistance in Ohm.
> > >
> > > +  semtech,input-analog-gain:
> > > +    $ref: /schemas/types.yaml#/definitions/uint32
> > > +    minimum: 0
> > > +    maximum: 3
> > > +    description: |
> > > +      Defines the input antenna analog gain
> > > +      0: x1.247
> > > +      1: x1 (default)
> > > +      2: x0.768
> > > +      3: x0.552
> > > +
> > >  required:
> > >    - compatible
> > >    - reg  
> >