Subject: Re: [PATCH 2/3] Input: rotary-encoder-counter: add DT bindings

From: Alexandre Belloni <[email-masked]>
Date: Fri, 10 Apr 2020 00:39:07 +0200

Hi Dmitry,

On 09/04/2020 15:21:15-0700, Dmitry Torokhov wrote:
> On Mon, Apr 06, 2020 at 05:58:05PM +0200, Kamel Bouhara wrote:
> > Add dt binding for the counter variant of the rotary encoder driver.
> > 
> > Signed-off-by: Kamel Bouhara <[email-masked]>
> > ---
> >  .../input/rotary-encoder-counter.yaml         | 67 +++++++++++++++++++
> >  1 file changed, 67 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/input/rotary-encoder-counter.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/input/rotary-encoder-counter.yaml b/Documentation/devicetree/bindings/input/rotary-encoder-counter.yaml
> > new file mode 100644
> > index 000000000000..a59f7c1faf0c
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/input/rotary-encoder-counter.yaml
> > @@ -0,0 +1,67 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/input/rotary-encoder-counter.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Rotary Encoder Counter
> > +
> > +maintainers:
> > +  - Kamel Bouhara <[email-masked]>
> > +
> > +description:
> > +  Registers a Rotary encoder connected through a counter device.
> > +
> > +properties:
> > +  compatible:
> > +    const: rotary-encoder-counter
> 
> I wonder if a separate driver is really needed. The original driver be
> taught to use counter device when available?
> 

By the original driver, do you mean drivers/input/misc/rotary_encoder.c
that is using gpios ?

> > +
> > +  counter:
> > +    description: Phandle for the counter device providing rotary position.
> > +
> > +  linux-axis:
> > +    description: The input subsystem axis to map to this rotary encoder.
> > +    type: boolean
> > +
> > +  qdec-mode:
> > +    description: |
> > +      Quadrature decoder function to set in the counter device.
> > +      3: x1-PHA
> > +      4: x1-PHB
> > +      5: x2-PHA
> > +      6: x2-PHB
> > +      7: x4-PHA and PHB
> 
> Is it really property of the rotary encoder itself or property of the
> counter device?
> 

The mode the quadrature decoder has to be put in depends on both the
rotary encoder and the qdec.

> > +
> > +  steps:
> > +    description: Number of steps in a full turnaround of the encoder.
> > +      Only relevant for absolute axis. Defaults to 24 which is a typical
> > +      value for such devices.
> > +
> > +  relative-axis:
> > +    description: Register a relative axis rather than an absolute one.
> > +    type: boolean
> > +
> > +  rollover:
> > +    description: Automatic rollover when the rotary value becomes greater
> > +      than the specified steps or smaller than 0. For absolute axis only.
> > +    type: boolean
> > +
> > +  poll-interval:
> > +    description: Poll interval at which the position is read from the counter
> > +      device (default 500ms).
> 
> Is there a way found counters to signal an interrupt?
> 

For some counters, there are interrupts available, this is not trivial
with the counter that is the target of this work but this is on the TODO
list. Of course, this will also require adding a bit more to the
in-kernel counter API to allow registering a callback that would be
called when an interrupt happens.

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

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