Re: [PATCH v9 3/4] dt-bindings: pps: pps-gpio PPS ECHO implementation

[tom burkart]

Hi Rob,

Quoting Rob Herring <robh@xxxxxxxxxx>:

> On Thu, Nov 22, 2018 at 3:49 AM Tom Burkart <tom@xxxxxxxxxx> wrote:
> > This patch implements the device tree changes required for the pps
> > echo functionality for pps-gpio, that sysfs claims is available
> > already.
> >
> > This patch was originally written by Lukas Senger as part of a masters
> > thesis project and modified for inclusion into the linux kernel by Tom
> > Burkart.
> >
> > Signed-off-by: Lukas Senger <lukas@xxxxxxxxxxxx>
> > Signed-off-by: Tom Burkart <tom@xxxxxxxxxx>
> > ---
> >  Documentation/devicetree/bindings/pps/pps-gpio.txt | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/pps/pps-gpio.txt  
> > b/Documentation/devicetree/bindings/pps/pps-gpio.txt
> > index 1155d49c2699..e09f6f2405c5 100644
> > --- a/Documentation/devicetree/bindings/pps/pps-gpio.txt
> > +++ b/Documentation/devicetree/bindings/pps/pps-gpio.txt
> > @@ -7,10 +7,15 @@ Required properties:
> >  - compatible: should be "pps-gpio"
> >  - gpios: one PPS GPIO in the format described by ../gpio/gpio.txt
> >
> > +Additional required properties for the PPS ECHO functionality:
> > +- echo-gpios: one PPS ECHO GPIO in the format described by ../gpio/gpio.txt
> > +- echo-active-ms: duration in ms of the active portion of the echo pulse
> > +
> >  Optional properties:
> >  - assert-falling-edge: when present, assert is indicated by a falling edge
> >                         (instead of by a rising edge)
> >  - capture-clear: when present, also capture the PPS clear event
> > +- invert-pps-echo: when present, invert the PPS ECHO pulse
>
> Why do you need this? Can't you just make the echo gpio GPIO_ACTIVE_LOW?
>
> BTW, using the flag probably should have been done for
> 'assert-falling-edge' as well.

The hardware I use expects a positive-going echo pulse, however, it  
was really easy to give users the option to have it inverted in case  
they use different hardware that expects a negative-going edge.

I may well be needing this option myself if I find that the GPS I am  
using produces better results for negative-going edges than  
positive-going edges.

Tom