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

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Date:	Thu, 16 Jun 2016 16:17:11 +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 Wednesday 25 May 2016 02:14 PM, Vignesh R wrote:
> 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.
> 

It would be great if you could comment on how would you like to see
support for absolute rotary-encoder(the one I described above)? As a new
driver or handle it by adding new compatible to existing rotary-encoder
driver?


-- 
Regards
Vignesh