Re: [PATCH 2/3] iio: adc: add STMPE ADC devicetree bindings

[Jonathan Cameron <jic23@jic23.retrosnub.co.uk>]

On Sun, 11 Nov 2018 15:42:07 +0000
Jonathan Cameron <jic23@kernel.org> wrote:

> On Tue,  6 Nov 2018 17:41:15 +0100
> Philippe Schenker <dev@pschenker.ch> wrote:
> 
> > From: Stefan Agner <stefan@agner.ch>
> > 
> > This adds the devicetree bindings for the STMPE ADC.
> > 
> > Signed-off-by: Stefan Agner <stefan@agner.ch>
> > Signed-off-by: Max Krummenacher <max.krummenacher@toradex.com>
> > Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
> > ---
> >  .../devicetree/bindings/iio/adc/stmpe-adc.txt | 34 +++++++++++++++++++
> >  1 file changed, 34 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/iio/adc/stmpe-adc.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/iio/adc/stmpe-adc.txt b/Documentation/devicetree/bindings/iio/adc/stmpe-adc.txt
> > new file mode 100644
> > index 000000000000..752ef35a794d
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/iio/adc/stmpe-adc.txt
> > @@ -0,0 +1,34 @@
> > +STMPE ADC driver
> > +----------------
> > +
> > +Required properties:
> > + - compatible: "st,stmpe-adc"
> > +
> > +Optional properties:
> > +Note that the ADC is shared with the STMPE touchscreen, so if using both the
> > +settings should be the same.  
> Ah, guessing there is already a binding in place for that which we need to closely
> match.  Should there be one overarching device with both as children though if
> it is the same hardware?

ah, there is an mfd, can these become elements of the binding for that so they
are only in one place? It's a bit ugly to do that given there are other
children, but certainly better than having them replicated like this...


> 
> > +If the settings are not the same, the settings of the driver initialized last
> > +will be active.
> > +- st,sample-time: ADC conversion time in number of clock. (0 -> 36 clocks,
> > +  1 -> 44 clocks, 2 -> 56 clocks, 3 -> 64 clocks, 4 -> 80 clocks,
> > +  5 -> 96 clocks, 6 -> 144 clocks), recommended is 4.  
> Could of questions here.  Is this a hardware dictated limit or is it dependent on
> application?  Basically I'm asking if it should be in userspace rather than here.
> 
> Ideally I'd love to see it in a unit of time, but failing that can we have it
> in clock cycles please rather than an enum?  Always nice if a binding is
> human readable.  st,sample-clock-cycles would be a better name.
> 
> 
> 
> > +- st,mod-12b: ADC Bit mode (0 -> 10bit ADC, 1 -> 12bit ADC)
> > +- st,ref-sel: ADC reference source (0 -> internal reference, 1 -> external
> > +  reference)  
> 
> If there is an external reference, I'd expect to see a regulator providing it.
> Usually the mere presence of such an optional regulator does the job of saying if
> it should be used.
> 
> 
> > +- st,adc-freq: ADC Clock speed (0 -> 1.625 MHz, 1 -> 3.25 MHz, 2 || 3 -> 6.5 MHz)  
> So this is some internal clock?  What dictates the right setting?  I.e. how
> should anyone know which one to pick?
> 
> > +- st,norequest-mask: bitmask specifying which ADC channels should _not_ be
> > +  requestable due to different usage (e.g. touch)  
> That's a little bit ugly.  Would prefer to see an explicit set of channels
> brought out as children in DT.  There are some patches around standardising
> some properties for doing that under review at the moment.
> 
> [PATCH v4 2/4] dt-bindings: iio: adc: Add common ADCs properties to a separate file
> 
> > +
> > +Node name must be stmpe_adc and should be child node of stmpe node to
> > +which it belongs.
> > +
> > +Example:
> > +
> > +	stmpe_adc {  
> 
> adc {
> is the moderately standard naming for ADCS.
> 
> > +		compatible = "st,stmpe-adc";
> > +		st,sample-time = <4>;
> > +		st,mod-12b = <1>;
> > +		st,ref-sel = <0>;
> > +		st,adc-freq = <1>;
> > +		st,norequest-mask = <0x0F>; /* dont use ADC CH3-0 */
> > +	};  
>