Re: [PATCH 2/5] Documentation: devicetree: Add property for controlling power saving mode for the us5182 als sensor

[Adriana Reus]

On 25.11.2015 02:01, Rob Herring wrote:
> On Tue, Nov 24, 2015 at 12:59:49PM +0200, Adriana Reus wrote:
> > Add a property to allow changing the default power-saving mode.
> > By default, at read raw the chip will activate and provide
> > one measurent, then it will shut itself down. However, the
> > chip can also work in "continuous" mode which may be more reliable
> > but is also more power consuming.
> >
> > Signed-off-by: Adriana Reus <adriana.reus@xxxxxxxxx>
> > ---
> >   Documentation/devicetree/bindings/iio/light/us5182d.txt | 11 +++++++++++
> >   1 file changed, 11 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/iio/light/us5182d.txt b/Documentation/devicetree/bindings/iio/light/us5182d.txt
> > index 6f0a530..a619799 100644
> > --- a/Documentation/devicetree/bindings/iio/light/us5182d.txt
> > +++ b/Documentation/devicetree/bindings/iio/light/us5182d.txt
> > @@ -7,13 +7,24 @@ Required properties:
> >   Optional properties:
> >   - upisemi,glass-coef: glass attenuation factor - compensation factor of
> >                         resolution 1000 for material transmittance.
> > +
> >   - upisemi,dark-ths: array of 8 elements containing 16-bit thresholds (adc
> >                       counts) corresponding to every scale.
> > +
> >   - upisemi,upper-dark-gain: 8-bit dark gain compensation factor(4 int and 4
> >                              fractional bits - Q4.4) applied when light > threshold
> > +
> >   - upisemi,lower-dark-gain: 8-bit dark gain compensation factor(4 int and 4
> >                              fractional bits - Q4.4) applied when light < threshold
> >
> > +- upisemi,continuous: This chip has two power modes: one-shot (chip takes one
> > +                      measurement and then shuts itself down) and continuous (
> > +                      chip takes continuous measurements). The one-shot mode is
> > +                      more power-friendly but the continuous mode may be more
> > +                      reliable. If this property is specified the continuous
> > +                      mode will be used instead of the default one-shot one for
> > +                      raw reads.
>
> I could imagine an OS may want to decide this on its own or use a
> mixture of the modes.
>
> Rob

There is no possibility of mixing them up (at the same time), so for 
example proximity cannot work in one mode and als the other.

The one-shot mode can only be used for raw reads (for example when 
user-space polls in_[proximity|light]_raw). If user-space wants to 
enable events (activate interrupts when certain thresholds are met - 
patch 5 of the series), then the chip has to switch to continuous 
nonetheless because it needs to be active all the time. So one work-flow 
scenario would be:

Consumer1 starts polling the raw interface - default_mode
Consumer2 activates events - continuous mode
Consumer2 deactivates events - back to default_mode

The only choice here is the default mode for raw reads, it currently is
one-shot, this patch allows for continuous to be used if preferred.
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