Re: [PATCH 1/3 v3] dt-bindings: abx80x: Add autocal-filter property

[Alexandre Belloni <alexandre.belloni@bootlin.com>]

Hi Rob,

On 13/07/2020 12:39:06-0600, Rob Herring wrote:
> On Mon, Jun 15, 2020 at 06:51:11AM -0400, Kevin P. Fleming wrote:
> > Add a property to allow control of the autocalibration filter
> > capacitor.
> > 
> > Signed-off-by: Kevin P. Fleming <kevin+linux@km6g.us>
> > Cc: Alessandro Zummo <a.zummo@towertech.it>
> > Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
> > Cc: Rob Herring <robh+dt@kernel.org>
> > To: linux-rtc@vger.kernel.org
> > To: devicetree@vger.kernel.org
> > ---
> > v3: corrected whitespace
> >  Documentation/devicetree/bindings/rtc/abracon,abx80x.txt | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/rtc/abracon,abx80x.txt b/Documentation/devicetree/bindings/rtc/abracon,abx80x.txt
> > index 2405e35a1bc0f..1b606e33d1a83 100644
> > --- a/Documentation/devicetree/bindings/rtc/abracon,abx80x.txt
> > +++ b/Documentation/devicetree/bindings/rtc/abracon,abx80x.txt
> > @@ -29,3 +29,11 @@ and valid to enable charging:
> >   - "abracon,tc-diode": should be "standard" (0.6V) or "schottky" (0.3V)
> >   - "abracon,tc-resistor": should be <0>, <3>, <6> or <11>. 0 disables the output
> >                            resistor, the other values are in kOhm.
> > +
> > +All of the devices can have a 47pf capacitor attached to increase the
> > +autocalibration accuracy of their RC oscillators. To enable or disable usage
> > +of the capacitor the following property can be defined:
> > +
> > + - "abracon,autocal-filter": should be <0> or <1>. 0 indicates that there
> > +                             is no capacitor attached, 1 indicates that there
> > +                             is a capacitor attached.
> 
> What does not present mean? If you don't have a defined meaning (such 
> as maintain the default/bootloader initialized setting), then make this 
> boolean.

We discussed that on the previous revision. Not present means keeping
the current value. Like most RTC registers, this is battery backed and
it is expected to persist across reboots. If it has ever been
initialized to a value, (e.g. by the bootloader), then we need a way to
have the driver not change it.

-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com