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

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Message-ID: <70fe4260-ffec-e069-25c6-bcc93ccbfb0a@ti.com>
Date:	Tue, 19 Jul 2016 18:34:40 +0530
From:	"R, Vignesh" <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

Dmitry,

On 6/16/2016 4:17 PM, Vignesh R 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.
>>

Could you please suggest the right solution here? Do you think new
driver is need to support above described absolute encoder h/w? It would
be great to have your input now, so that I can work on the new set of
patches and submit them for v4.9 merge window as soon as v4.8 merge
window closes?

Regards
Vignesh