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:	Wed, 25 Nov 2009 22:58:29 +0100
From:	Gerd Hoffmann <kraxel@...hat.com>
To:	Devin Heitmueller <dheitmueller@...nellabs.com>
CC:	Jarod Wilson <jarod@...sonet.com>,
	Krzysztof Halasa <khc@...waw.pl>,
	Christoph Bartelmus <lirc@...telmus.de>, awalls@...ix.net,
	dmitry.torokhov@...il.com, j@...nau.net, jarod@...hat.com,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-media@...r.kernel.org, mchehab@...hat.com, 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 11/25/09 19:20, Devin Heitmueller wrote:
> On Wed, Nov 25, 2009 at 1:07 PM, Jarod Wilson<jarod@...sonet.com>
> wrote:
>> Took me a minute to figure out exactly what you were talking
>> about. You're referring to the current in-kernel decoding done on
>> an ad-hoc basis for assorted remotes bundled with capture devices,
>> correct?
>>
>> Admittedly, unifying those and the lirc driven devices hasn't
>> really been on my radar.

I think at the end of the day we'll want to have all IR drivers use the
same interface.  The way the current in-kernel input layer drivers work
obviously isn't perfect too, so we *must* consider both worlds to get a
good solution for long-term ...

> This is one of the key use cases I would be very concerned with. For
> many users who have bought tuner products, the bundled remotes work
> "out-of-the-box", regardless of whether lircd is installed.

I bet this simply isn't going to change.

> I have no objection so much as to saying "well, you have to install
> the lircd service now", but there needs to be a way for the driver to
>  automatically tell lirc what the default remote control should be,
> to avoid a regression in functionality.

*Requiring* lircd for the current in-kernel drivers doesn't make sense
at all.  Allowing lircd being used so it can do some more advanced stuff 
makes sense though.

> This is why I think we really should put together a list of use
> cases, so that we can see how any given proposal addresses those use
> cases. I offered to do such, but nobody seemed really interested in
> this.

Lets have a look at the problems the current input layer bits have 
compared to lirc:

(1) ir code (say rc5) -> keycode conversion looses information.

I think this can easily be addressed by adding a IR event type to the 
input layer, which could look like this:

   input_event->type  = EV_IR
   input_event->code  = IR_RC5
   input_event->value = <rc5 value>

In case the 32bit value is too small we might want send two events 
instead, with ->code being set to IR_<code>_1 and IR_<code>_2

Advantages:
   * Applications (including lircd) can get access to the unmodified
     rc5/rc6/... codes.
   * All the ir-code -> keycode mapping magic can be handled by the
     core input layer then.  All the driver needs to do is to pass on
     the information which keymap should be loaded by default (for the
     bundled remote if any).  The configuration can happen in userspace
     (sysfs attribute + udev + small utility in tools/ir/).
   * lirc drivers which get ir codes from the hardware can be converted
     to pure input layer drivers without regressions.  lircd is not
     required any more.

(2) input layer doesn't give access to the raw samples.

Not sure how to deal with that best.  Passing them through the input 
layer would certainly be possible to hack up.  But what would be the 
point?  The input layer wouldn't do any processing on them.  It wouldn't 
buy us much.  So we might want to simply stick with todays lirc 
interface for the raw samples.

Drivers which support both ir codes (be it by hardware or by in-kernel 
decoding) and raw samples would register two devices then, one input 
device and one lirc device.  It would probably a good idea to stop 
sending events to the input layer as soon as someone (most likely lircd) 
opens the lirc device to avoid keystrokes showing up twice.

By default the in-kernel bits will be at work, but optionally you can 
have lircd grab the raw samples and do fancy advanced decoding.

(3) input layer doesn't allow transmitting IR codes.

If we keep the lirc interface for raw samples anyway, then we can keep 
it for sending too, problem solved ;)  How does sending hardware work 
btw?  Do they all accept just raw samples?  Or does some hardware also 
accept ir-codes?

cheers,
   Gerd
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