linux-kernel - Re: [PATCH v6 6/9] dt-bindings: counter: Document stm32 quadrature encoder

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Date:   Sun, 20 May 2018 16:47:23 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        William Breathitt Gray <vilhelm.gray@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        devicetree@...r.kernel.org,
        Benjamin Gaignard <benjamin.gaignard@...com>,
        linux-iio@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Fabrice Gasnier <fabrice.gasnier@...com>
Subject: Re: [PATCH v6 6/9] dt-bindings: counter: Document stm32 quadrature
 encoder

On Fri, 18 May 2018 11:28:15 -0500
Rob Herring <robh@...nel.org> wrote:

> On Thu, May 17, 2018 at 08:59:40PM +0200, Benjamin Gaignard wrote:
> > 2018-05-17 18:23 GMT+02:00 Rob Herring <robh+dt@...nel.org>:  
> > > On Wed, May 16, 2018 at 12:51 PM, William Breathitt Gray
> > > <vilhelm.gray@...il.com> wrote:  
> > >> From: Benjamin Gaignard <benjamin.gaignard@...com>  
> > >
> > > v6? Where's v1-v5?
> > >  
> > >> Add bindings for STM32 Timer quadrature encoder.
> > >> It is a sub-node of STM32 Timer which implement the
> > >> counter part of the hardware.
> > >>
> > >> Cc: Rob Herring <robh+dt@...nel.org>
> > >> Cc: Mark Rutland <mark.rutland@....com>
> > >> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...com>
> > >> Signed-off-by: William Breathitt Gray <vilhelm.gray@...il.com>
> > >> ---
> > >>  .../bindings/counter/stm32-timer-cnt.txt      | 26 +++++++++++++++++++
> > >>  .../devicetree/bindings/mfd/stm32-timers.txt  |  7 +++++
> > >>  2 files changed, 33 insertions(+)
> > >>  create mode 100644 Documentation/devicetree/bindings/counter/stm32-timer-cnt.txt
> > >>
> > >> diff --git a/Documentation/devicetree/bindings/counter/stm32-timer-cnt.txt b/Documentation/devicetree/bindings/counter/stm32-timer-cnt.txt
> > >> new file mode 100644
> > >> index 000000000000..377728128bef
> > >> --- /dev/null
> > >> +++ b/Documentation/devicetree/bindings/counter/stm32-timer-cnt.txt
> > >> @@ -0,0 +1,26 @@
> > >> +STMicroelectronics STM32 Timer quadrature encoder
> > >> +
> > >> +STM32 Timer provides quadrature encoder counter mode to detect  
> > >
> > > 'mode' does not sound like a sub-block of the timers block.  
> > 
> > quadrature encoding is one of the counting modes of this hardware
> > block which is enable to count on other signals/triggers  
> 
> You don't need a child node and compatible to set a mode.

A pile of extra hardware becomes relevant and you only want
to be in this state if you have appropriate external device
wired up.  In this case there is admittedly not a lot here
but some devices will look a bit more like a touchscreen controller.

They are often build on top of an ADC module, but have a load
of touch screen only signals and electrical elements that
warrant being represented as a separate node in the DT.

> 
> > >> +angular position and direction of rotary elements,
> > >> +from IN1 and IN2 input signals.
> > >> +
> > >> +Must be a sub-node of an STM32 Timer device tree node.
> > >> +See ../mfd/stm32-timers.txt for details about the parent node.
> > >> +
> > >> +Required properties:
> > >> +- compatible:          Must be "st,stm32-timer-counter".
> > >> +- pinctrl-names:       Set to "default".
> > >> +- pinctrl-0:           List of phandles pointing to pin configuration nodes,
> > >> +                       to set IN1/IN2 pins in mode of operation for Low-Power
> > >> +                       Timer input on external pin.
> > >> +
> > >> +Example:
> > >> +       timers@...10000  {
> > >> +               compatible = "st,stm32-timers";
> > >> +               ...
> > >> +               counter {
> > >> +                       compatible = "st,stm32-timer-counter";  
> > >
> > > Is there only 1? How is the counter addressed?  
> > 
> > Yes there is only one counter per hardware block.
> > Counter is addressed like the two others sub-nodes and the details
> > about parent mode are describe in stm32-timers.txt
> > Should I add them here too ? so example will be like that:  
> 
> No, you should drop the child node and add pinctrl to the parent.
> 
> Any other functions this block has that you plan on adding? Please make 
> bindings as complete as possible, not what you currently have drivers 
> for.
> 
> > timers@...10000  {
> >   #address-cells = <1>;
> >   #size-cells = <0>;
> >   compatible = "st,stm32-timers";
> >   reg = <0x40010000 0x400>;
> >   clocks = <&rcc 0 160>;
> >   clock-names = "int";
> >   counter {
> >     compatible = "st,stm32-timer-counter";
> >     pinctrl-names = "default";
> >     pinctrl-0 = <&tim1_in_pins>;
> >     };
> >  };
> > 
> > Benjamin  
> > >
> > > _______________________________________________
> > > linux-arm-kernel mailing list
> > > linux-arm-kernel@...ts.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel  

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