Re: [RFC v2] Another approach to IR

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

On Wed, Dec 02, 2009 at 12:30:29PM -0500, Jon Smirl wrote:
> On Wed, Dec 2, 2009 at 12:10 PM, Dmitry Torokhov
> <dmitry.torokhov@gmail.com> wrote:
> > On Wed, Dec 02, 2009 at 10:44:58AM -0200, Mauro Carvalho Chehab wrote:
> >> Dmitry Torokhov wrote:
> >> > 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.
> >>
> >> The raw interface applies only to the devices that doesn't have a hardware decoder
> >> (something between 40%-60% of the currently supported devices).
> >
> > 50% is quite a number I think. But if driver does not allow access to
> > the raw stream - it will refuse binding to lirc_dev interface.
> >
> >>
> >> > - 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
> >>
> >> I don't see why having more than one interface, especially for devices with
> >> hardware decoders.
> >>
> >> On IR remote receivers, internally, there's just one interface per hardware.
> >>
> >> Considering the hardware decoding case, why to artificially create other
> >> interfaces that can't be used simultaneously? No current hardware
> >> decoders can do that (or, at least, no current implementation allows).
> >> We're foreseen some cases where we'll have that (like Patrick's dib0700 driver),
> >> but for now, it is not possible to offer more than one interface to userspace.
> >> Creating an arbitrary number of artificial interfaces just to pass a parameter
> >> to the driver (the protocol), really seems overkill to me.
> >
> > We need to cater to the future cases as well. I don't want to redesign
> > it in 2 years. But for devices that have only hardware decoders I
> > suppose we can short-curcuit "interfaces" and have a library-like module
> > creating input devices directly.
> >
> >>
> >> In the case of the cheap devices with just raw interfaces, running in-kernel
> >> decoders, while it will work if you create one interface per protocol
> >> per IR receiver, this also seems overkill. Why to do that? It sounds that it will
> >> just create additional complexity at the kernelspace and at the userspace, since
> >> now userspace programs will need to open more than one device to receive the
> >> keycodes.
> >
> > _Yes_!!! You open as many event devices as there are devices you are
> > interested in receiving data from. Multiplexing devices are bad, bad,
> > bad. Witness /dev/input/mouse and all the attempts at working around the
> > fact that if you have a special driver for one of your devices you
> > receive events from the same device through 2 interfaces and all kind of
> > "grab", "super-grab", "smart-grab" schemes are born.
> >
> >>
> >> > (for each remote/substream that they can recognize).
> >>
> >> I'm assuming that, by remote, you're referring to a remote receiver (and not to
> >> the remote itself), right?
> >
> > If we could separate by remote transmitter that would be the best I
> > think, but I understand that it is rarely possible?
> 
> The code I posted using configfs did that. Instead of making apps IR
> aware it mapped the vendor/device/command triplets into standard Linux
> keycodes.  Each remote was its own evdev device.
>

That is what I liked about the patchset.
 
> That scheme could be made to "just work" by building in a couple of
> mapping tables. The driver would pre-populate configfs entries for a
> some standard IR devices. Set the remote for Motorala DVR. Default
> Myth to look for the evdev device associated with Motorola DVR. The
> built-in mapping table would then map from pulse timing to Linux
> keycodes.
> 
> If everyone hates configfs the same mapping can be done via the set
> keys IOCTL and making changes to the user space apps like loadkeys.
> 

It is not the hate of configfs per se, but rather concern that configfs
takes too much resources and is not normally enabled.

-- 
Dmitry