linux-kernel - Re: [PATCH v3 0/2] AM335x-ICE: Add support for rotary switch

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Message-ID: <86711a29-8fb5-9804-8642-2f390081e677@zonque.org>
Date:   Wed, 24 Aug 2016 13:01:44 +0200
From:   Daniel Mack <daniel@...que.org>
To:     Vignesh R <vigneshr@...com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Tony Lindgren <tony@...mide.com>,
        Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Daniel Hung-yu Wu <hywu@...gle.com>,
        Grant Grundler <grundler@...omium.org>,
        S Twiss <stwiss.opensource@...semi.com>,
        Moritz Fischer <moritz.fischer@...us.com>,
        Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        "Andrew F . Davis" <afd@...com>, linux-input@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Subject: Re: [PATCH v3 0/2] AM335x-ICE: Add support for rotary switch

On 08/24/2016 11:15 AM, Vignesh R wrote:
> On Wednesday 24 August 2016 02:05 PM, Daniel Mack wrote:
>> On 08/24/2016 09:58 AM, Vignesh R wrote:
>>> This series adds support for rotary-switch on AM335x-ICE that is
>>> connected to TI PCA9536 I2C GPIO expander.
>>> First patch adds new generic driver to read status of group of GPIO
>>> lines and report the value as an input event. The second patch adds DT
>>> entries for the same.
>>>
>>> v2: https://lkml.org/lkml/2016/8/23/111
>>> v1: https://lkml.org/lkml/2016/8/12/7
>>
>> Is there a reason why the rotary-encoder driver cannot handle this?
>> Commit 7dde4e74744 ("Input: rotary-encoder - support more than 2 gpios
>> as input") added support for that mode AFAIU.
>>
> 
> Rotary encoder driver handles incremental encoders only and does not
> support absolute encoders. The rotary switch on am335x-ice is different
> from the incremental encoders in the
> sense that GPIO line status directly reflect the position(number)
> pointed by the dial of the encoder. So, there is no need to count steps
> or know the direction of rotation as it does not matter.
> 
> I did try to enhance rotary-encoder driver to support absolute
> encoder[1] but the comment there was to write new driver that simply
> translates gpio-encoded value into ABS* event. Indeed, the new driver
> looks more simple and can handle more such hardwares.

Okay. Yes, that makes sense. Thanks for the explanation!


Daniel