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Date: Wed, 2 Dec 2009 01:38:04 -0800
From: Dmitry Torokhov <dmitry.torokhov@gmail.com>
To: Mauro Carvalho Chehab <mchehab@redhat.com>
Cc: Devin Heitmueller <dheitmueller@kernellabs.com>,
       Jon Smirl <jonsmirl@gmail.com>,
       Maxim Levitsky <maximlevitsky@gmail.com>, awalls@radix.net,
       j@jannau.net, jarod@redhat.com, jarod@wilsonet.com, khc@pm.waw.pl,
       linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
       linux-media@vger.kernel.org, lirc-list@lists.sourceforge.net,
       superm1@ubuntu.com, Christoph Bartelmus <lirc@bartelmus.de>
Subject: Re: [RFC v2] Another approach to IR
Message-ID: <20091202093803.GA8656@core.coreip.homeip.net>
References: <9e4733910912010708u1064e2c6mbc08a01293c3e7fd@mail.gmail.com> <1259682428.18599.10.camel@maxim-laptop> <9e4733910912010816q32e829a2uce180bfda69ef86d@mail.gmail.com> <4B154C54.5090906@redhat.com> <829197380912010909m59cb1078q5bd2e00af0368aaf@mail.gmail.com> <4B155288.1060509@redhat.com> <20091201175400.GA19259@core.coreip.homeip.net> <4B1567D8.7080007@redhat.com> <20091201201158.GA20335@core.coreip.homeip.net> <4B15852D.4050505@redhat.com>
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On Tue, Dec 01, 2009 at 07:05:49PM -0200, Mauro Carvalho Chehab wrote:
> Dmitry Torokhov wrote:
> > On Tue, Dec 01, 2009 at 05:00:40PM -0200, Mauro Carvalho Chehab wrote:
> >> Dmitry Torokhov wrote:
> >>> On Tue, Dec 01, 2009 at 03:29:44PM -0200, Mauro Carvalho Chehab wrote:
> >>>> For sure we need to add an EVIOSETPROTO ioctl to allow the driver 
> >>>> to change the protocol in runtime.
> >>>>
> >>> Mauro,
> >>>
> >>> I think this kind of confuguration belongs to lirc device space,
> >>> not input/evdev. This is the same as protocol selection for psmouse
> >>> module: while it is normally auto-detected we have sysfs attribute to
> >>> force one or another and it is tied to serio device, not input
> >>> device.
> >> Dmitry,
> >>
> >> This has nothing to do with the raw interface nor with lirc. This problem 
> >> happens with the evdev interface and already affects the in-kernel drivers.
> >>
> >> In this case, psmouse is not a good example. With a mouse, when a movement
> >> occurs, you'll receive some data from its port. So, a software can autodetect
> >> the protocol. The same principle can be used also with a raw pulse/space
> >> interface, where software can autodetect the protocol.
> > 
> > Or, in certain cases, it can not.
> > 
> > [... skipped rationale for adding a way to control protocol (with which
> > I agree) ...]
> > 
> >> To solve this, we really need to extend evdev API to do 3 things: enumberate the
> >> supported protocols, get the current protocol(s), and select the protocol(s) that
> >> will be used by a newer table.
> >>
> > 
> > And here we start disagreeing. My preference would be for adding this
> > API on lirc device level (i.e. /syc/class/lirc/lircX/blah namespace),
> > since it only applicable to IR, not to input devices in general.
> > 
> > Once you selected proper protocol(s) and maybe instantiated several
> > input devices then udev (by examining input device capabilities and
> > optionally looking up at the parent device properties) would use
> > input evdev API to load proper keymap. Because translation of
> > driver-specific codes into standard key definitions is in the input
> > realm. Reading these driver-specific codes from hardware is outside of
> > input layer domain.
> > 
> > Just as psmouse ability to specify protocol is not shoved into evdev;
> > just as atkbd quirks (force release key list and other driver-specific
> > options) are not in evdev either; we should not overload evdev interface
> > with IR-specific items.
> 
> I'm not against mapping those features as sysfs atributes, but they don't belong
> to lirc, as far as I understand. From all we've discussed, we'll create a lirc
> interface to allow the direct usage of raw IO. However, IR protocol is a property
> that is not related to raw IO mode but, instead, to evdev mode.
>

Why would protocol relate to evdev node? Evdev does not really care what
how the fact that a certain button was pressed was communicated to it.
It may be deliveretd through PS/2 port, or maybe it was Bluetooth HID,
or USB HID or USB boot protocol or some custom protocol, or RC-5, NEC or
some custom IR protocol. It makes no difference _whatsoever_ to evdev
nor any users of evdev care about protocol used by underlying hardware
device to transmit the data.
 
> We might add a /sys/class/IR and add IR specific stuff there, but it seems
> overkill to me and will hide the fact that those parameters are part of the evdev
> interface.
> 
> So, I would just add the IR sysfs parameters at the /sys/class/input, if
> the device is an IR (or create it is /sys/class/input/IR).
> 
> I agree that the code to implement the IR specific sysfs parameter should be kept
> oustide input core, as they're specific to IR implementations.
> 
> Would this work for you?

I am seeing a little bit differently structured subsystem for IR at the
moment. I think we should do something like this:

- receivers create /sys/class/lirc devices. These devices provide API
  with a ring buffer (fifo) for the raw data stream coming from (and to)
  them.
- we allow registering several data interfaces/decoders that can be bound
  (manually or maybe automatically) to lirc devices. lirc devices may
  provide hints as to which interface(s) better suited for handling the
  data coming form particular receiver. Several interfaces may be bound
  to one device at a time.
- one of the interfaces is interface implementing current lirc_dev
- other interfaces may be in-kernel RC-5 decoder or other decoders.
  decoders will create instances of input devices (for each
  remote/substream that they can recognize).

This way there is clear layering, protocol selection is kept at lirc
level.

Would this work?

-- 
Dmitry
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