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

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Date:	Tue, 8 Dec 2009 09:12:36 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Mauro Carvalho Chehab <mchehab@...hat.com>
Cc:	Jon Smirl <jonsmirl@...il.com>, Krzysztof Halasa <khc@...waw.pl>,
	hermann pitton <hermann-pitton@...or.de>,
	Christoph Bartelmus <lirc@...telmus.de>, awalls@...ix.net,
	j@...nau.net, jarod@...hat.com, jarod@...sonet.com,
	kraxel@...hat.com, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	superm1@...ntu.com
Subject: Re: [RFC] What are the goals for the architecture of an in-kernel
	IR  system?

On Tue, Dec 08, 2009 at 09:58:53AM -0200, Mauro Carvalho Chehab wrote:
> Dmitry Torokhov wrote:
> > On Mon, Dec 07, 2009 at 09:44:14PM -0200, Mauro Carvalho Chehab wrote:
> 
> >>> What about capabilities of the receiver, what frequencies?
> >>> If a receiver has multiple frequencies, how do you report what
> >>> frequency the data came in on?
> >> IMO, via sysfs.
> > 
> > We probably need to think what exactly we report through sysfs siunce it
> > is ABI of sorts.
> 
> Yes, sure.
> 
> Probably, the exact needs will popup only when we start to actually writing that
> part of the core.
> 
> My intention for now is to just create a /sys/class/irrcv, with one node
> per each IR receiver and adding a protocol enumeration/selection node
> there, and add some capabilities for the in-kernel decoders and lirc_dev
> to create new nodes under that class.
> 
> When the decoders/lirc_dev patches popup, we'll need to review those sysfs
> API's.
>  
> >>> What about multiple apps simultaneously using the pulse data?
> >> IMO, the better is to limit the raw interface to just one open.
> >>
> > 
> > Why woudl we want to do this? Quite often there is a need for "observer"
> > that maybe does not act on data but allows capturing it. Single-user
> > inetrfaces are PITA. 
> 
> That should work fine as well, but I'm not sure how we'll detect overrun with
> several kfifo readers.
> 

Push the data into readers so they can do te decoding at their own pace.
Some can do it in interrupt context, some will need workqueue/thread.
They can also regilate the depth of the buffer, according to their
needs.

> >>> How big is the receive queue?
> >> It should be big enough to receive at least one keycode event. Considering that
> >> the driver will use kfifo (IMO, it is a good strategy, especially since you
> >> won't need any lock if just one open is allowed), it will require a power of two size.
> >>
> > 
> > Would not it be wither driver- or protocol-specific?
> 
> Probably.
> 
> > 
> >>> How does access work, root only or any user?
> >> IMO, it should be the same requirement as used by an input interface.
> >>
> >>> How are capabilities exposed, sysfs, etc?
> >> IMO, sysfs.
> >>
> >>> What is the interface for attaching an in-kernel decoder?
> >> IMO, it should use the kfifo for it. However, if we allow both raw data and
> >> in-kernel decoders to read data there, we'll need a spinlock to protect the
> >> kfifo.
> >>
> > 
> > I think Jon meant userspace interface for attaching particular decoder.
> 
> I don't think we need an userspace interface for the in-kernel decoders. All
> it needs is to enable/disable the protocol decoders, imo via sysfs interface.
> 
> >>> If there is an in-kernel decoder should the pulse data stop being
> >>> reported, partially stopped, something else?
> >> I don't have a strong opinion here, but, from the previous discussions, it
> >> seems that people want it to be double-reported by default. If so, I think
> >> we need to implement a command at the raw interface to allow disabling the
> >> in-kernel decoder, while the raw interface is kept open.
> > 
> > Why don't you simply let consumers decide where they will get their data?
> 
> How?
> 

You end up with N evdev devices. Let application (MythTV) say "I want to
use /dev/input/event1" (well, it will need persistent udev rule, but
that's a detail). Another application will chose another event node.
User can decide she'd rather use lircd - and so configire applications
to use event5. Any maybe turned off the in-kernel decoders if they are
of no use and there is a concern that they consume too mcuh resoures.

Won't this work? 

-- 
Dmitry
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