linux-kernel - Re: [RFC] What are the goals for the architecture of an in-kernel IR system?

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Message-Id: <200911291601.53368.mike@mtgambier.net>
Date:	Sun, 29 Nov 2009 16:01:53 +1030
From:	Mike Lampard <mike@...ambier.net>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Jon Smirl <jonsmirl@...il.com>,
	Christoph Bartelmus <christoph@...telmus.de>,
	jarod@...sonet.com, awalls@...ix.net, j@...nau.net,
	jarod@...hat.com, khc@...waw.pl, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	mchehab@...hat.com, superm1@...ntu.com
Subject: Re: [RFC] What are the goals for the architecture of an in-kernel IR system?

On Sun, 29 Nov 2009 03:25:49 pm Dmitry Torokhov wrote:
> On Sun, Nov 29, 2009 at 01:17:03PM +1030, Mike Lampard wrote:
> > On Sat, 28 Nov 2009 02:27:59 am Jon Smirl wrote:
> > > On Fri, Nov 27, 2009 at 2:45 AM, Christoph Bartelmus
> > >
> > > <christoph@...telmus.de> wrote:
> > > > Hi Mauro,
> > > >
> > > > on 26 Nov 09 at 14:25, Mauro Carvalho Chehab wrote:
> > > >> Christoph Bartelmus wrote:
> > > >
> > > > [...]
> > > >
> > > >>> But I'm still a bit hesitant about the in-kernel decoding. Maybe
> > > >>> it's just because I'm not familiar at all with input layer toolset.
> > > >
> > > > [...]
> > > >
> > > >> I hope it helps for you to better understand how this works.
> > > >
> > > > So the plan is to have two ways of using IR in the future which are
> > > > incompatible to each other, the feature-set of one being a subset of
> > > > the other?
> > >
> > > Take advantage of the fact that we don't have a twenty year old legacy
> > > API already in the kernel. Design an IR API that uses current kernel
> > > systems. Christoph, ignore the code I wrote and make a design proposal
> > > that addresses these goals...
> > >
> > > 1) Unified input in Linux using evdev. IR is on equal footing with
> > > mouse and keyboard.
> >
> > I think this a case where automating setup can be over-emphasised (in the
> > remote-as-keyboard case).
> >
> > Apologies in advance if I've misunderstood the idea of utilising the
> > 'input subsystem' for IR.  If the plan is to offer dedicated IR events
> > via a yet-to- be-announced input event subsystem and to optionally
> > disallow acting as a keyboard via a module option or similar then please
> > ignore the following.
> >
> > Whilst having remotes come through the input subsystem might be 'the
> > correct thing' from a purely technical standpoint, as an end-user I find
> > the use-case for remotes completely different in one key aspect: 
> > Keyboards and mice are generally foreground-app input devices, whereas
> > remotes are often controlling daemons sitting in the background piping
> > media through dedicated devices.  As an example I have a VDR instance
> > running in the background on my desktop machine outputting to a TV in
> > another room via a pci mpeg decoder - I certainly don't want the VDR
> > remote control interacting with my X11 desktop in any way unless I go out
> > of my way to set it up to do so, nor do I want it interacting with other
> > applications (such as MPD piping music around the house) that are
> > controlled via other remotes in other rooms unless specified.
> >
> > Setting this up with Lircd was easy, how would a kernel-based proposal
> > handle this?
> 
> Why would that be different really? On my keyboard there is a key for
> e-mail application (and many others) - what HID calls Application Launch
> keys IIRC. There also application control keys and system control keys,
> KEY_COFFEE aka KEY_SCREENLOCK. Those are not to be consumed by
> foreground application but by daemons/session-wide application.
> 
In my real-world examples above, both VDR and MPD are started at system start 
and are not associated with any user-initiated sessions (X login etc) - they 
are not X11 clients.  Their only input is via Lircd.  Conversely todays 
Xserver (if I read my logfiles correctly) consumes all input event devices by 
default, turning them into keypresses for its client apps.  This is exactly 
the wrong behaviour for my use-case.  In order to ensure that my daemons 
receive their input I must first ensure that X doesn't receive those events - 
assuming this is possible it still complicates matters further than they are 
today (I'd need a simple way of automatically differentiating between remote 
devices and keyboard devices) .

Mike
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