linux-kernel - Re: [RFC PATCH 5/6] extcon-gpio: Describe devicetree bindings

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Date:	Thu, 12 Sep 2013 09:53:04 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Mark Rutland <mark.rutland@....com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	Pawel Moll <Pawel.Moll@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ian.campbell@...rix.com>,
	MyungJoo Ham <myungjoo.ham@...sung.com>,
	Chanwoo Choi <cw00.choi@...sung.com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>
Subject: Re: [RFC PATCH 5/6] extcon-gpio: Describe devicetree bindings

On Thu, Sep 12, 2013 at 05:41:00PM +0100, Mark Rutland wrote:
> On Fri, Aug 30, 2013 at 05:29:37AM +0100, Guenter Roeck wrote:
> > Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> > ---
> >  .../devicetree/bindings/extcon/extcon-gpio         |   23 ++++++++++++++++++++
> >  1 file changed, 23 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/extcon/extcon-gpio
> > 
> > diff --git a/Documentation/devicetree/bindings/extcon/extcon-gpio b/Documentation/devicetree/bindings/extcon/extcon-gpio
> > new file mode 100644
> > index 0000000..091ddc6
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/extcon/extcon-gpio
> > @@ -0,0 +1,23 @@
> > +Device-Tree bindings for extcon/extcon-gpio driver
> 
> Bindings shouldn't refer to Linux-specifics like particular drivers.
> What class of hardware are you actually trying to describe?
> 
Agreed. Question is where to put the bindings, as they are not really 
specific to the extcon driver. The extcon driver merely implements 
the bindings. This is why the "compatible" statement reads "gpio-connector"
and not "extcon-something".

The bindings describe a connector managed through gpio pins.

> > +
> > +Required properties:
> > +	- compatible = "gpio-connector";
> > +	- presence-detect-gpios - presence detect gpio pin
> > +
> > +Optional properties:
> > +	- debounce-interval - debounce interval in milli-seconds
> > +	- state-on - on (connected) state
> > +	- state-off - off (disconnected) state
> > +	  Depending on the type of connector or cable, states may
> > +	  for example be reported as "connected"/"disconnected"
> > +	  or "inserted"/"removed".
> 
> I don't understand what the state-* properties describe. Do these
> provide semantic information to drivers? What is the full set of valid
> values?
> 
That is merely text which is ultimately passed on to the user.
Guess 'semantic information' might be a way to phrase it.

> > +
> > +Example node:
> > +
> > +	some-connector {
> > +		compatible = "gpio-connector";
> > +		presence-detect-gpios = <&gpio1 7 1>;
> > +		debounce-interval = <1>;
> > +		state-on = "connected";
> > +		state-on = "disconnected";
> > +	};
> 
> I'm not sure how much value this adds to bindings over describing the
> gpios directly. This seems to add a layer of indirection because of
> Linux internals.
> 
Not sure I understand what you mean with "describing the gpios directly".
Can you elaborate and/or provide an example ?

How would you describe the use of gpio pins used to detect board presence ?
That doesn't seem very Linux specific to me.

Thanks,
Guenter
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