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

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Date:	Mon, 30 Nov 2009 08:23:05 -0500
From:	Jon Smirl <jonsmirl@...il.com>
To:	Andy Walls <awalls@...ix.net>
Cc:	Mauro Carvalho Chehab <mchehab@...hat.com>,
	Ray Lee <ray-lk@...rabbit.org>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Krzysztof Halasa <khc@...waw.pl>,
	Christoph Bartelmus <lirc@...telmus.de>,
	dmitry.torokhov@...il.com, j@...nau.net, jarod@...hat.com,
	jarod@...sonet.com, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	stefanr@...6.in-berlin.de, superm1@...ntu.com
Subject: Re: [RFC] What are the goals for the architecture of an in-kernel IR 
	system?

On Mon, Nov 30, 2009 at 7:57 AM, Andy Walls <awalls@...ix.net> wrote:
> I suppose my best answer to that is question back to you: Why does udev
> run in userspace versus a kernel thread?

Because udev is a scripting system. I've always said that the
scripting piece of IR belongs in user space. IR scripting should be
optional, none of the systems I work on need it.

This is the event flow being built...

device timing data
 -- send timing data to user space
 -- do protocol decode (40K code)
 -- send decoded data back to kernel
other devices that decode in HW add events here
 -- send decoded data to user space
 -- map to keys (30K code)
 -- send keys back to kernel
apps listen for keys
 -- send keys back to user space
 -- user space apps act on key (possibly run scripts)

I'd like to see...

device timing data
-- user space can inject timing data from user space drivers
do protocol decode (40K code)
other devices that decode in HW add events here
-- user space can inject decoded data from user space drivers
map to keys (30K code)
apps listen for keys
 -- send keys back to user space
 -- user space apps act on key (possibly run scripts)



>
> My personal thoughts on why user space is more flexible:
>
> 1. You have all of *NIX available to you to use as tools to achieve your
> requirements.
>
> 2. You are not constrained to use C.
>
> 3. You can link in libraries with functions that are not available in
> the kernel.  (udev has libudev IIRC to handle complexities)
>
> 4. Reading a configuration file or other file from the filesystem is
> trivial - file access from usespace is easy.
>
> 5. You don't have to be concerned about the running context (am I
> allowed to sleep here or not?).
>
>
>
>
>
>
>> A kernelspace input device driver can start working since boot time.
>> On the other hand, an userspace device driver will be available only
>> after mounting the filesystems and starting the deamons
>> (e. g. after running inittab).
>>
>> So, you cannot catch a key that would be affecting the boot
>> (for example to ask the kernel to run a different runlevel or entering
>> on some administrative mode).
>
> Right.  That's another requirement that makes sense, if we're talking
> about systems that don't have any other keyboard handy to the user.
>
> So are we optimizing for the embedded/STB and HTPC with no keyboard use
> case, or the desktop or HTPC with a keyboard for maintencance?
>
>
> Regards,
> Andy
>
>
> --
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-- 
Jon Smirl
jonsmirl@...il.com
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