linux-kernel - Re: [RFC v2] Another approach to IR

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Date:	Thu, 03 Dec 2009 07:02:49 -0500
From:	Andy Walls <awalls@...ix.net>
To:	Mauro Carvalho Chehab <mchehab@...hat.com>
Cc:	Jarod Wilson <jarod@...sonet.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Devin Heitmueller <dheitmueller@...nellabs.com>,
	Jon Smirl <jonsmirl@...il.com>,
	Maxim Levitsky <maximlevitsky@...il.com>, j@...nau.net,
	jarod@...hat.com, khc@...waw.pl, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	lirc-list@...ts.sourceforge.net, superm1@...ntu.com,
	Christoph Bartelmus <lirc@...telmus.de>
Subject: Re: [RFC v2] Another approach to IR

On Thu, 2009-12-03 at 08:00 -0200, Mauro Carvalho Chehab wrote:
> Andy Walls wrote:
> > On Wed, 2009-12-02 at 14:55 -0500, Jarod Wilson wrote:
> >> On Dec 2, 2009, at 2:33 PM, Mauro Carvalho Chehab wrote:

 
> > Both of those IR devices are/will be encapsulated in a v4l2_subdevice
> > object internally.  I was going to write lirc_v4l glue between the
> > v4l2_device/v4l2_subdev_ir_ops and lirc_dev.
> > 
> > As for the the I2C chips, I was going to go back and encapsulate those
> > in the v4l2_subdevice object as well, so then my notional lirc_v4l could
> > pick those up too.  The I2C subsystem only allows one binding to an I2C
> > client address/name on a bus.  So without some new glue like a notional
> > lirc_v4l, it *may* be hard to share between ir-kbd-i2c and lirc_i2c and
> > lirc_zilog.
> 
> Maybe you're having a bad time because you may be trying to integrate lirc
> at the wrong place.

These were just ideas.  I haven't done *anything* yet. ;)


> All devices at V4L tree including ir-kbd-i2c use ir-common.ko 
> (at /drivers/media/common tree) module to communicate to IR's. 
> I'm preparing some patches to extend this also to dvb-usb devices 
> (that uses a close enough infrastructure). 
> 
> Also, most of the decoding code are there, in a form of helper routines.
> 
> As the idea is to provide lirc interface to all devices that can work with
> raw pulse/space, the proper place is to write a subroutine there that, once
> called, will make those pulse/space raw codes available to lirc and will
> call the needed decoders to export them also to evdev.
> 
> The code at ir-common module was originally built to be used by V4L, but I'm
> porting the code there to be generic enough to be a library that can be used
> by other drivers. So, lirc_zilog and other lirc devices that will need to open
> evdev interfaces after running a decoder can use them.

I think I see what you are saying (I wish could see look at a whiteboard
somewhere...).  Wherever we come through internally to split to 2
different userspace interfaces is fine, if you've got a big picture plan
you think is feasible.

That seems like a bit of perturbation to lirc_zilog and lirc_i2c.  My
thought was that lirc_v4l using the standardized v4l2_subdev_ir_ops
interface, and maybe some new calls associted with v4l2_device, could
subsume/unify all the functionality of lirc_i2c, lirc_zilog, ...
lirc_whatever.

Maybe that's just a poorly thought out dream though...


> Due to that, we shouldn't add v4l2_subdevice there. Nothing prevents to create
> a v4l2-ir-subdev glue if you want to see the IR's as subdevices, but this should
> be implemented as a separate module.

The v4l_subdevice just abstracted the IR hardware into a nice (mental)
box for me -- easier to keep hardware separate from software decoders
and userspace interface logic.

Also, since v4l2_subdevices may have per subdevice /dev nodes and
the /dev/../mcN nodes providing a discovery mechanism due to the Meda
Controller framework, wrapping things in v4l2_subdevice may be handy for
development and debug.  Or ... as an additional operational interface to
userspace. :D  *ducks and runs for cover*

Regards,
Andy

> Cheers,
> Mauro.


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