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

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Message-ID: <20091207075100.GB24958@core.coreip.homeip.net>
Date:	Sun, 6 Dec 2009 23:51:00 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Christoph Bartelmus <lirc@...telmus.de>
Cc:	awalls@...ix.net, j@...nau.net, jarod@...hat.com,
	jarod@...sonet.com, jonsmirl@...il.com, khc@...waw.pl,
	kraxel@...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] What are the goals for the architecture of an in-kernel
	IR  system?

On Sun, Dec 06, 2009 at 12:58:00PM +0100, Christoph Bartelmus wrote:
> Hi Dmitry,
> 
> on 04 Dec 09 at 15:15, Dmitry Torokhov wrote:
> [...]
> >>>>>> http://lirc.sourceforge.net/remotes/lg/6711A20015N
> >>>>>>
> >>>>>> This is an air-conditioner remote.
> >>>>>> The entries that you see in this config file are not really separate
> >>>>>> buttons. Instead the remote just sends the current settings for e.g.
> >>>>>> temperature encoded in the protocol when you press some up/down key.
> >>>>>> You really don't want to map all possible temperature settings to KEY_*
> >>>>>> events. For such cases it would be nice to have access at the raw scan
> >>>>>> codes from user space to do interpretation of the data.
> >>>>>> The default would still be to pass the data to the input layer, but it
> >>>>>> won't hurt to have the possibility to access the raw data somehow.
> >>>>
> >>>>> Interesting. IMHO, the better would be to add an evdev ioctl to return
> >>>>> the scancode for such cases, instead of returning the keycode.
> >>>>
> >>>> That means you would have to set up a pseudo keymap, so that you can get
> >>>> the key event which you could than react on with a ioctl. Or are you
> >>>> generating KEY_UNKNOWN for every scancode that is not mapped?
> >>>> What if different scan codes are mapped to the same key event? How do you
> >>>> retrieve the scan code for the key event?
> >>>> I don't think it can work this way.
> >>>>
> >>
> >>> EV_MSC/MSC_SCAN.
> >>
> >> How would I get the 64 bit scan codes that the iMON devices generate?
> >> How would I know that the scan code is 64 bit?
> >> input_event.value is __s32.
> >>
> 
> > I suppose we could add MSC_SCAN_END event so that we can transmit
> > "scancodes" of arbitrary length. You'd get several MSC_SCAN followed by
> > MSC_SCAN_END marker. If you don't get MSC_SCAN_END assume the code is 32
> > bit.
> 
> And I set a timeout to know that no MSC_SCAN_END will arrive? This is  
> broken design IMHO.
> 

EV_SYN signals the end of state transmission.

> Furthermore lircd needs to know the length of the scan code in bits, not  
> as a multiple of 32.

I really do not think that LIRCD is the type of application that should
be using evdev interface, but rather other way around.

> 
> > FWIW there is MSC_RAW as well.
> 
> It took me some time to convice people that this is not the right way to  
> handle raw timing data.
> 
> Christoph

-- 
Dmitry
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