linux-kernel - Re: [RFC PATCH 1/2] Input: rotary-encoder- Add support for absolute encoder

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Message-ID: <574565ED.3060205@ti.com>
Date:	Wed, 25 May 2016 14:14:29 +0530
From:	Vignesh R <vigneshr@...com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
CC:	Rob Herring <robh+dt@...nel.org>, Tony Lindgren <tony@...mide.com>,
	Jonathan Corbet <corbet@....net>,
	Johan Hovold <johan@...nel.org>,
	Sylvain Rochet <sylvain.rochet@...secur.com>,
	Masanari Iida <standby24x7@...il.com>,
	Ezequiel Garcia <ezequiel@...guardiasur.com.ar>,
	S Twiss <stwiss.opensource@...semi.com>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Moritz Fischer <moritz.fischer@...us.com>,
	Arnd Bergmann <arnd@...db.de>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Timo Teras <timo.teras@....fi>,
	Guido Martinez <guido@...guardiasur.com.ar>,
	Clifton Barnes <clifton.a.barnes@...il.com>,
	Uwe Kleine-Konig <u.kleine-koenig@...gutronix.de>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH 1/2] Input: rotary-encoder- Add support for absolute
 encoder

Hi Dmitry,

On 05/23/2016 02:48 PM, R, Vignesh wrote:
> 
> 
> On 5/20/2016 10:04 PM, Dmitry Torokhov wrote:
>> On Thu, May 19, 2016 at 02:34:00PM +0530, Vignesh R wrote:
>>> There are rotary-encoders where GPIO lines reflect the actual position
>>> of the rotary encoder dial. For example, if dial points to 9, then four
>>> GPIO lines connected to the rotary encoder will read HLLH(1001b = 9).
>>> Add support for such rotary-encoder.
>>> The driver relies on rotary-encoder,absolute-encoder DT property to
>>> detect such encoders.
>>> Since, GPIO IRQs are not necessary to work with
>>> such encoders, optional polling mode support is added using
>>> input_poll_dev skeleton. This is can be used by enabling
>>> CONFIG_INPUT_GPIO_ROTARY_ENCODER_POLL_MODE_SUPPORT.
>>
>> Does this really belong to a rotary encoder and not a new driver that
>> simply translates gpio-encoded value into ABS* event?
>>
> 
> Currently rotary encoder driver only supports incremental/step counting
> rotary devices. However, the device that is there on am335x-ice is an
> absolute encoder but, IMO, nevertheless a kind of rotary encoder. The
> only difference is that there is no need to count steps and the absolute
> position value is always available as binary encoded state of connected
> GPIOs.
> The hardware on am335x-ice is a mechanical rotary encoder switch
> connected over 4 GPIOs. It is same as binary encoder described at [1]
> (except there are 4 GPIO lines), so this lead me to add support in
> rotary-encoder.
> 
> [1]https://en.wikipedia.org/wiki/Rotary_encoder#Standard_binary_encoding
> 

Could you please comment on how would you like to support above
described encoder: As a new driver or with existing driver with new
compatible/mode setting via DT or as suggest by Uwe in another reply?
IMHO, supporting using existing driver with new mode/compatible string
looks a better option as the hardware is a kind of rotary-encoder.

-- 
Regards
Vignesh