linux-kernel - Re: [RFC PATCH] input: Add disable sysfs entry for every input device

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Message-ID: <20180102214852.pnsocg7qaxt5y6qh@pali>
Date:   Tue, 2 Jan 2018 22:48:52 +0100
From:   Pali Rohár <pali.rohar@...il.com>
To:     Bastien Nocera <hadess@...ess.net>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Sebastian Reichel <sre@...nel.org>,
        Pavel Machek <pavel@....cz>,
        Mauro Carvalho Chehab <mchehab@....samsung.com>,
        Chuck Ebbert <cebbert.lkml@...il.com>,
        Henrik Rydberg <rydberg@...omail.se>,
        Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] input: Add disable sysfs entry for every input device

On Tuesday 03 January 2017 12:21:21 Bastien Nocera wrote:
> On Mon, 2017-01-02 at 18:09 +0100, Pali Rohár wrote:
> > On Monday 02 January 2017 16:27:05 Bastien Nocera wrote:
> > > On Sun, 2016-12-25 at 11:04 +0100, Pali Rohár wrote:
> > > > This patch allows user to disable events from any input device so
> > > > events
> > > > would not be delivered to userspace.
> > > > 
> > > > Currently there is no way to disable particular input device by
> > > > kernel.
> > > > User for different reasons would need it for integrated PS/2
> > > > keyboard or
> > > > touchpad in notebook or touchscreen on mobile device to prevent
> > > > sending
> > > > events. E.g. mobile phone in pocket or broken integrated PS/2
> > > > keyboard.
> > > > 
> > > > This is just a RFC patch, not tested yet. Original post about
> > > > motivation
> > > > about this patch is there: https://lkml.org/lkml/2014/11/29/92
> > > 
> > > Having implemented something of that ilk in user-space (we
> > > automatically disable touch devices when the associated screen is
> > > turned off/suspended), I think this might need more thought.
> > 
> > How to implement such thing in userspace? I think you cannot do that 
> > without rewriting every one userspace application which uses input.
> > 
> > > What happens when a device is opened and the device disabled
> > through
> > > sysfs, are the users revoked?
> > 
> > Applications will not receive events. Same as if input device does
> > not 
> > generates events.
> > 
> > > Does this put the device in suspend in the same way that closing
> > the
> > > device's last user does?
> > 
> > Current code not (this is just RFC prototype), but it should be
> > possible 
> > to implement.
> > 
> > > Is this not better implemented in user-space at the session level,
> > > where it knows about which output corresponds to which input
> > device?
> > 
> > How to do that without rewriting existing applications?
> > 
> > > Is this useful enough to disable misbehaving devices on hardware,
> > so
> > > that the device is not effective on boot?  
> > 
> > In case integrated device is absolutely unusable and generates
> > always 
> > random events, it does not solve problem at boot time.
> > 
> > But more real case is laptop with closed LID press buttons and here
> > it 
> > is useful.
> 
> There's usually a display manager in between the application and the
> input device.

But that is not always truth. In some cases there are applications which
opens input device directly.

> Whether it's X.org, or a Wayland compositor. Even David's
>  https://github.com/dvdhrm/kmscon could help for console applications.

That kmscon needs KMS, right? So it would not work on hardware which do
not have KMS drivers.

-- 
Pali Rohár
pali.rohar@...il.com