linux-kernel - Re: [RFC] Should we create a raw input interface for IR's ? - Was: Re: [PATCH 1/3 v2] lirc core device driver infrastructure

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Date:	Tue, 8 Dec 2009 09:16:52 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Jon Smirl <jonsmirl@...il.com>
Cc:	Andy Walls <awalls@...ix.net>, Jarod Wilson <jarod@...sonet.com>,
	Mauro Carvalho Chehab <mchehab@...hat.com>,
	Krzysztof Halasa <khc@...waw.pl>,
	Christoph Bartelmus <lirc@...telmus.de>, j@...nau.net,
	jarod@...hat.com, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	superm1@...ntu.com
Subject: Re: [RFC] Should we create a raw input interface for IR's ? - Was:
	Re: [PATCH 1/3 v2] lirc core device driver infrastructure

On Tue, Dec 08, 2009 at 07:52:02AM -0500, Jon Smirl wrote:
> On Tue, Dec 8, 2009 at 7:35 AM, Andy Walls <awalls@...ix.net> wrote:
> > On Mon, 2009-12-07 at 20:22 -0800, Dmitry Torokhov wrote:
> >> On Mon, Dec 07, 2009 at 09:42:22PM -0500, Andy Walls wrote:
> >
> >> > So I'll whip up an RC-6 Mode 6A decoder for cx23885-input.c before the
> >> > end of the month.
> >> >
> >> > I can setup the CX2388[58] hardware to look for both RC-5 and RC-6 with
> >> > a common set of parameters, so I may be able to set up the decoders to
> >> > handle decoding from two different remote types at once.  The HVR boards
> >> > can ship with either type of remote AFAIK.
> >> >
> >> > I wonder if I can flip the keytables on the fly or if I have to create
> >> > two different input devices?
> >> >
> >>
> >> Can you distinguish between the 2 remotes (not receivers)?
> >
> > Yes.  RC-6 and RC-5 are different enough to distinguish between the two.
> > (Honestly I could pile on more protocols that have similar pulse time
> > periods, but that's complexity for no good reason and I don't know of a
> > vendor that bundles 3 types of remotes per TV card.)
> >
> >
> >>  Like I said,
> >> I think the preferred way is to represent every remote that can be
> >> distinguished from each other as a separate input device.
> >
> > OK.  With RC-5, NEC, and RC-6 at least there is also an address or
> > system byte or word to distingish different remotes.  However creating
> > multiple input devices on the fly for detected remotes would be madness
> > - especially with a decoding error in the address bits.
> 
> I agree that creating devices on the fly has problems. Another
> solution is to create one device for each map that is loaded. There
> would be a couple built-in maps for bundled remotes - each would
> create a device. Then the user could load more maps with each map
> creating a device.
> 
> Incoming scancodes are matched against all of the loaded maps and a
> keycode event is generated if a match occurs.
> 

How many sancodes do we need to reliably recognize the device though? I
am not sure users would want to press 5 random buttons in order to start
using the remote, unless it happens exactly once and then we manage to
store the data somewhere.

> This illustrates why there should an EV_IR event which communicates
> scancodes, without this event you can't see the scancodes that don't
> match a map entry. A scancode would be first matched against the map,
> then if there as no match an EV_IR event would be reported.

Just report MSC_SCAN always. As I said elsewhere we can extend it to be
multi-dword if needed (just need to agree on endianness).

-- 
Dmitry
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