Re: [PATCH v7 1/4] dt-bindings: pps: descriptor-based gpio, capture-clear addition

[tom burkart]

Hi Rob,

Quoting Rob Herring <robh@xxxxxxxxxx>:

> On Sat, Nov 17, 2018 at 6:35 PM tom burkart <tom@xxxxxxxxxx> wrote:
> > Quoting Rob Herring <robh@xxxxxxxxxx>:
> >
> > > On Sat, Nov 17, 2018 at 4:35 AM tom burkart <tom@xxxxxxxxxx> wrote:
> > >>
> > >> Quoting Rob Herring <robh@xxxxxxxxxx>:
> > >>
> > >> > On Wed, Nov 14, 2018 at 11:54:29PM +1100, Tom Burkart wrote:
> > >> >> This patch changes the devicetree bindings for the pps-gpio driver
> > >> >> from the integer based ABI to the descriptor based ABI.
> > >> > ? That has nothing to do with DT.
> > >>
> > >> I believe it does, as the change in ABI forces a rename in the DT
> > >> naming convention.
> > >> This is due to the descriptor based ABI appending "-gpio" or  
> > "-gpios" (see
> > >> Documentation/gpio/base.txt.)
> > >> Admittedly, I may have called it by the wrong name due to ignorance,
> > >> my apologies.
> > >
> > > If what you say is correct, then you can't change this driver. You'll
> > > break compatibility with any existing DT.
> > >
> > > Changing the binding reasoning should purely be that this is the
> > > preferred form. Bindings must be independent from changing kernel
> > > APIs.
> >
> > See comments from Philip Zabel.  I misread the documentation and this
> > has now been corrected in v8 of the patch.  I hope that eliminates all
> > comments made above.
> >
> > >> >>  It also adds
> > >> >> documentation for the device tree capture-clear option.  The legacy
> > >> >> device tree entry for the GPIO pin is supported.
> > >> >>
> > >> >> Signed-off-by: Tom Burkart <tom@xxxxxxxxxx>
> > >> >> ---
> > >> >>  Documentation/devicetree/bindings/pps/pps-gpio.txt | 8 ++++++--
> > >> >>  1 file changed, 6 insertions(+), 2 deletions(-)
> > >> >>
> > >> >> diff --git a/Documentation/devicetree/bindings/pps/pps-gpio.txt
> > >> >> b/Documentation/devicetree/bindings/pps/pps-gpio.txt
> > >> >> index 3683874832ae..6c9fc0998d94 100644
> > >> >> --- a/Documentation/devicetree/bindings/pps/pps-gpio.txt
> > >> >> +++ b/Documentation/devicetree/bindings/pps/pps-gpio.txt
> > >> >> @@ -5,19 +5,23 @@ a GPIO pin.
> > >> >>
> > >> >>  Required properties:
> > >> >>  - compatible: should be "pps-gpio"
> > >> >> -- gpios: one PPS GPIO in the format described by ../gpio/gpio.txt
> > >> >> +- pps-gpios: one PPS GPIO in the format described by ../gpio/gpio.txt
> > >> >> +Alternatively (DEPRECATED), instead of pps-gpios above, it may have:
> > >> >> +- gpios: one PPS GPIO as above
> > >> >>
> > >> >>  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
> > >> >
> > >> > Is this a h/w thing? or driver configuration?
> > >>
> > >> Driver configuration.  Most of the code was present in the driver, yet
> > >> it was not documented, or usable due to a two line (code) omission
> > >> (the value was not being fetched from DT).
> > >
> > > So what determines how you want to configure this? If the user will
> > > want to change it, then it should be a sysfs attr and exposed to
> > > userspace. If it depends on h/w config for a board then it can be in
> > > DT.
> >
> > Sorry, I misled you somewhat.  If the PPS pulse active transition from
> > the hardware is on the falling edge, this flag is required to get the
> > OS to use that as the active transition.  This would not change at the
> > user's whim but rather it is dependent on connected hardware.
>
> This description sounds more like 'assert-falling-edge' than 'capture-clear'.
>
> I'm still not clear on what 'capture-clear' is.

Ignoring my patch for a minute, the pps_gpio_irq_handler will only  
report a pps PPS_CAPTURECLEAR event if 'capture-clear' is set.  As the  
current pps-gpio driver is not able to set this flag, it cannot ever  
report a PPS_CAPTURECLEAR event.

My patch adds the ability to set this flag and adds the documentation  
to go with it.
Admittedly, I do not require this functionality for what I want, but  
working with the code, I noticed the omission and decided to add it  
for someone else to use it, if they need it.

I am happy to remove this out of my patch, if you feel this to be the  
best way forward.

Tom