linux-kernel - Re: [PATCH v2] Input: add 'safe' user switch codes

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Date:   Fri, 5 Nov 2021 16:04:23 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Jeff LaBundy <jeff@...undy.com>
Cc:     Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        linux-input@...r.kernel.org, Geert Uytterhoeven <geert@...der.be>,
        linux-renesas-soc@...r.kernel.org,
        Max Gurtovoy <mgurtovoy@...dia.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Wu Hao <hao.wu@...el.com>, Bjorn Helgaas <bhelgaas@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Ertman <david.m.ertman@...el.com>,
        Maximilian Luz <luzmaximilian@...il.com>,
        Stephan Gerhold <stephan@...hold.net>,
        Xu Yilun <yilun.xu@...el.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] Input: add 'safe' user switch codes

Hi Jeff, Kieran,

On Fri, Nov 05, 2021 at 12:00:37PM -0500, Jeff LaBundy wrote:
> Hi Kieran,
> 
> On Fri, Nov 05, 2021 at 10:35:07AM +0000, Kieran Bingham wrote:
> > All existing SW input codes define an action which can be interpreted by
> > a user environment to adapt to the condition of the switch.
> > 
> > For example, switches to define the audio mute, will prevent audio
> > playback, and switches to indicate lid and covers being closed may
> > disable displays.
> > 
> > Many evaluation platforms provide switches which can be connected to the
> > input system but associating these to an action incorrectly could
> > provide inconsistent end user experiences due to unmarked switch
> > positions.
> > 
> > Define two custom user defined switches allowing hardware descriptions
> > to be created whereby the position of the switch is not interpreted as
> > any standard condition that will affect a user experience.
> > 
> > This allows wiring up custom generic switches in a way that will allow
> > them to be read and processed, without incurring undesired or otherwise
> > undocumented (by the hardware) 'default' behaviours.
> > 
> > Signed-off-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
> > ---
> > 
> > Sigh, a compile test might have at least saved the buildbots the trouble
> > of notifying me I also need to update the INPUT_DEVICE_ID_SW_MAX. But
> > even so - I'm really looking for a discussion on the best ways to
> > describe a non-defined switch in device tree.
> > 
> > Here's a compiling v2 ;-) But the real questions are :
> > 
> >  - Should an existing feature switch be used for generic switches?
> >  - Should we even have a 'user' defined switch?
> >  - If we add user switches, how many?
> > 
> 
> This is merely my opinion, but if a hardware switch does not have a defined
> purpose, it does not seem necessary to represent it with an input device.

Yes, exactly. For input core we are trying to avoid generic events with
no defined meaning.

What are these switches? GPIOs? Maybe it would be better to use GPIO
layer to test the state for them?

Thanks.

-- 
Dmitry