linux-kernel - Re: [RFC PATCH v2 1/4] dt-bindings: input: Add support for the MPR121 without interrupt line

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Date:   Sat, 27 Jul 2019 11:01:54 +0300
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Michal Vokáč <michal.vokac@...ft.com>,
        Mark Rutland <mark.rutland@....com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        linux-input@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Pengutronix Kernel Team <kernel@...gutronix.de>
Subject: Re: [RFC PATCH v2 1/4] dt-bindings: input: Add support for the
 MPR121 without interrupt line

On Thu, Jun 13, 2019 at 04:39:45PM -0600, Rob Herring wrote:
> On Fri, May 17, 2019 at 03:12:50PM +0200, Michal Vokáč wrote:
> > Normally, the MPR121 controller uses separate interrupt line to notify
> > the I2C host that a key was touched/released. To support platforms that
> > can not use the interrupt line, polling of the MPR121 registers can be
> > used.
> 
> 'separate' from what?
> 
> > 
> > Signed-off-by: Michal Vokáč <michal.vokac@...ft.com>
> > ---
> > Changes since v1:
> > - Document the polled binding in the original file, do not create a new one.
> >   (Rob)
> > 
> >  Documentation/devicetree/bindings/input/mpr121-touchkey.txt | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> > 
> > diff --git a/Documentation/devicetree/bindings/input/mpr121-touchkey.txt b/Documentation/devicetree/bindings/input/mpr121-touchkey.txt
> > index b7c61ee5841b..97f55273d473 100644
> > --- a/Documentation/devicetree/bindings/input/mpr121-touchkey.txt
> > +++ b/Documentation/devicetree/bindings/input/mpr121-touchkey.txt
> > @@ -1,9 +1,14 @@
> > -* Freescale MPR121 Controllor
> > +* Freescale MPR121 Controller
> >  
> >  Required Properties:
> > -- compatible:		Should be "fsl,mpr121-touchkey"
> > +- compatible:		Should be one of:
> > +			- "fsl,mpr121-touchkey" - MPR121 with interrupt line
> > +			- "fsl,mpr121-touchkey-polled" - MPR121 with polling
> >  - reg:			The I2C slave address of the device.
> >  - interrupts:		The interrupt number to the cpu.
> > +			In case of "fsl,mpr121-touchkey-polled" the interrupt
> > +			line is not used and hence the interrupts property is
> > +			not required.
> 
> Absence of the interrupts property is enough to determine polled mode 
> and you don't need a separate compatible string.

I would prefer if we could distinguish between chip working in polled
mode intentionally vs DT writer simply forgetting to specify interrupt
property. Should we key the polling mode off "linux,poll-interval"
property? We probably going to need it anyway as not everyone needs the
same polling frequency.

Thanks.

-- 
Dmitry