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From: Geert Uytterhoeven <firstname.lastname@example.org>
To: Jeff LaBundy <email@example.com>
Cc: Kieran Bingham <firstname.lastname@example.org>,
Dmitry Torokhov <email@example.com>,
Max Gurtovoy <firstname.lastname@example.org>,
Hans de Goede <email@example.com>, Wu Hao <firstname.lastname@example.org>,
Bjorn Helgaas <email@example.com>,
Dan Williams <firstname.lastname@example.org>,
Dave Ertman <email@example.com>,
Maximilian Luz <firstname.lastname@example.org>,
Stephan Gerhold <email@example.com>,
Xu Yilun <firstname.lastname@example.org>,
open list <email@example.com>
Subject: Re: [PATCH v2] Input: add 'safe' user switch codes
Date: Mon, 8 Nov 2021 12:00:20 +0100 [thread overview]
Message-ID: <CAMuHMdUUbzTGWSybSpEgaN1oCzV9o+tdKJHEsdVvPD--52RbQg@mail.gmail.com> (raw)
On Sun, Nov 7, 2021 at 7:17 AM Jeff LaBundy <firstname.lastname@example.org> wrote:
> On Sat, Nov 06, 2021 at 10:13:15AM +0000, Kieran Bingham wrote:
> > Quoting Dmitry Torokhov (2021-11-05 23:04:23)
> > > On Fri, Nov 05, 2021 at 12:00:37PM -0500, Jeff LaBundy wrote:
> > > > 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 <email@example.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.
> > That's understandable, particularly as I could then ponder - how do we
> > even define generic switches, and how many ;-) I wanted to discuss it
> > because otherwise these switches will be defined in DT as buttons. And
> > they are not buttons...
> > > What are these switches? GPIOs? Maybe it would be better to use GPIO
> > > layer to test the state for them?
> > They are physical slide switches on the board. But they have no defined
> > purpose by the hardware designer. The purpose would be defined by the
> > end user, as otherwise they are generic test switches.
> > These have been previously handled as gpio-key buttons, for instance
> > key-1 to key-4 at  are actually four slides switches.
> >  https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e3414b8c45afa5cdfb1ffd10f5334da3458c4aa5
> > What I'm trying to determine/promote is that they are not push buttons,
> > and shouldn't be described as such. I have posted  to add support for
> > these switches, but I am limited to chosing 'functions' which will have
> > an impact on the system...
> >  https://firstname.lastname@example.org/
> > Presently in  I have chosen SW_LID and SW_DOCK as very arbitrary
> > functions for the switches. But my concern is that in doing so, the
> > SW_LID position could for instance suggest to a window environment or
> > power management system that the lid is closed, and the system should
> > be suspended (of course depending upon configurations). That would mean
> > that the board would now be potentially always heading into a suspend
> > after power up which would not be at all clear from the switch.
> > I believe a 'switch' is the correct way to define this hardware, so that
> > both positions can be determined, and read, and events generated on
> > state change - but that there shouldn't be any artificially imposed side
> > effects from the description.
> > If the answer is "no we can't have generic switches" then so be it, but
> > it feels wrong to further propogate the definition of these test
> > switches as keys.
> I agree that a slide switch tied to a GPIO is indeed a switch in terms of
> input core. Note, however, that definitions from your first example (such
> as KEY_1) are not any less generic; those have specific meanings too.
But at least the KEY_* events are less likely to cause harmful side
effects than the SW_* events. I have no idea which daemon in e.g. a
generic Ubuntu userspace would act on the SW_* events.
> If the concern is that toggling a switch effects undesired behavior, such
> as turning a display on or off, then the switch should not be represented
> with a gpio-keys node in the first place.
> Stated another way, the fact that the GPIO are connected to something does
> not necessarily mean they need to be supported. Only once they map to some
> function should they be defined, in my opinion.
Following the mantra "DT describes hardware, not software policy", I
think we should describe generic switches in DT, and perhaps have a way
to configure the actual event code from userspace (e.g. using sysfs?).
Without such configuration, perhaps they could emit a SW_* event with
the MSB set, so at least their state can be queried using e.g. evtest?
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- email@example.com
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
next prev parent reply other threads:[~2021-11-08 11:00 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-05 10:35 Kieran Bingham
2021-11-05 17:00 ` Jeff LaBundy
2021-11-05 23:04 ` Dmitry Torokhov
2021-11-06 10:13 ` Kieran Bingham
2021-11-07 6:17 ` Jeff LaBundy
2021-11-08 11:00 ` Geert Uytterhoeven [this message]
2021-11-08 12:35 ` Kieran Bingham
2021-11-08 12:41 ` Geert Uytterhoeven
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