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

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Mon, Dec 07, 2009 at 09:42:22PM -0500, Andy Walls wrote:
> On Mon, 2009-12-07 at 13:19 -0500, Jarod Wilson wrote:
> > On Nov 26, 2009, at 2:43 PM, Andy Walls wrote:
> > 
> > > On Thu, 2009-11-26 at 12:05 -0200, Mauro Carvalho Chehab wrote:
> > >> Krzysztof Halasa wrote:
> > >>> Andy Walls <awalls@radix.net> writes:
> > >>> 
> > >>>> I would also note that RC-6 Mode 6A, used by most MCE remotes, was
> > >>>> developed by Philips, but Microsoft has some sort of licensing interest
> > >>>> in it and it is almost surely encumbered somwhow:
> > >>> 
> > >>> I don't know about legal problems in some countries but from the
> > >>> technical POV handling the protocol in the kernel is more efficient
> > >>> or (/and) simpler.
> > >> 
> > >> A software licensing from Microsoft won't apply to Linux kernel, so I'm
> > >> assuming that you're referring to some patent that they could be filled
> > >> about RC6 mode 6A.
> > >> 
> > >> I don't know if is there any US patent pending about it (AFAIK, only US
> > >> accepts software patents), but there are some prior-art for IR key
> > >> decoding. So, I don't see what "innovation" RC6 would be adding. 
> > >> If it is some new way to transmit waves, the patent issues
> > >> aren't related to software, and the device manufacturer had already handled
> > >> it when they made their devices.
> > >> 
> > >> If it is just a new keytable, this issue 
> > >> could be easily solved by loading the keytable via userspace.
> > >> 
> > >> Also, assuming that you can use the driver only with a hardware that comes
> > >> with a licensed software, the user has already the license for using it.
> > >> 
> > >> Do you have any details on what patents they are claiming?
> > > 
> > > The US Philips RC-6 patent is US Patent 5,877,702
> > > 
> > > http://www.google.com/patents?vid=USPAT5877702
> > > 
> > > Click on download PDF to get a copy of the whole patent.
> > > 
> > > I am not a lawyer.  Philips claims' all appear to tie to a transmitter
> > > or receiver as part of a system, but most of the claims are about
> > > information and bit positions and lengths.
> > ...
> > > IMO, given
> > > 
> > > a. the dearth of public information about RC-6, indicating someone
> > > thinks it's their trade secret or intellectual property
> > > 
> > > b. Microsoft claiming to license something related to the MCE remote
> > > protocols (which are obviously RC-6 Mode 6A),
> > > 
> > > c. my inability to draw a "clear, bright line" that RC-6 Mode 6A
> > > encoding and decoding, as needed by MCE remotes, implemented in software
> > > doesn't violate anyone's government granted rights to exclusivity.
> > > 
> > > I think it's much better to implement software RC-6 Mode 6A encoding and
> > > decoding in user space, doing only the minimum needed to get the
> > > hardware setup and going in the kernel.  
> > > 
> > > Encoding/decoding of RC-6 by microcontrollers with firmware doesn't
> > > worry me. 
> > > 
> > > 
> > > Maybe I'm being too conservative here, but I have a personal interest in
> > > keeping Linux free and unencumbered even in the US which, I cannot deny,
> > > has a patent system that is screwed up.
> > 
> > So I had one of the people who does all the license and patent audits
> > for Fedora packages look at the Philips patent on RC-6. He's 100%
> > positive that the patent *only* covers hardware, there should be no
> > problem whatsoever writing a software decoder for RC-6.
> 
> OK.  Thanks for having some professionals take a look.  (I'm assuming
> that's the only patent.)
> 
> 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)? 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. Applications
expect to query device capabilities and expect them to stay somewhat
stable (we do support keymap change but I don't think anyone expectes
flip-flopping).

-- 
Dmitry