Message-ID: <4B1E656F.3020507@redhat.com>
Date:	Tue, 08 Dec 2009 12:40:47 -0200
From:	Mauro Carvalho Chehab <mchehab@...hat.com>
To:	Jon Smirl <jonsmirl@...il.com>
CC:	Andy Walls <awalls@...ix.net>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Jarod Wilson <jarod@...sonet.com>,
	Krzysztof Halasa <khc@...waw.pl>,
	Christoph Bartelmus <lirc@...telmus.de>, j@...nau.net,
	jarod@...hat.com, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	superm1@...ntu.com
Subject: Re: [RFC] Should we create a raw input interface for IR's ? - Was:
 	Re: [PATCH 1/3 v2] lirc core device driver infrastructure

Jon Smirl wrote:
> On Tue, Dec 8, 2009 at 9:16 AM, Mauro Carvalho Chehab
> <mchehab@...hat.com> wrote:
>> Jon Smirl wrote:
>>> On Tue, Dec 8, 2009 at 8:40 AM, Mauro Carvalho Chehab
>>> <mchehab@...hat.com> wrote:
>>>> Jon Smirl wrote:
>>>>> On Tue, Dec 8, 2009 at 7:35 AM, Andy Walls <awalls@...ix.net> wrote:
>>>>>> On Mon, 2009-12-07 at 20:22 -0800, Dmitry Torokhov wrote:
>>>>>>> On Mon, Dec 07, 2009 at 09:42:22PM -0500, Andy Walls wrote:
>>>>>>>> So I'll whip up an RC-6 Mode 6A decoder for cx23885-input.c before the
>>>>>>>> end of the month.
>>>>>>>>
>>>>>>>> I can setup the CX2388[58] hardware to look for both RC-5 and RC-6 with
>>>>>>>> a common set of parameters, so I may be able to set up the decoders to
>>>>>>>> handle decoding from two different remote types at once.  The HVR boards
>>>>>>>> can ship with either type of remote AFAIK.
>>>>>>>>
>>>>>>>> I wonder if I can flip the keytables on the fly or if I have to create
>>>>>>>> two different input devices?
>>>>>>>>
>>>>>>> Can you distinguish between the 2 remotes (not receivers)?
>>>>>> Yes.  RC-6 and RC-5 are different enough to distinguish between the two.
>>>>>> (Honestly I could pile on more protocols that have similar pulse time
>>>>>> periods, but that's complexity for no good reason and I don't know of a
>>>>>> vendor that bundles 3 types of remotes per TV card.)
>>>>>>
>>>>>>
>>>>>>>  Like I said,
>>>>>>> I think the preferred way is to represent every remote that can be
>>>>>>> distinguished from each other as a separate input device.
>>>>>> OK.  With RC-5, NEC, and RC-6 at least there is also an address or
>>>>>> system byte or word to distingish different remotes.  However creating
>>>>>> multiple input devices on the fly for detected remotes would be madness
>>>>>> - especially with a decoding error in the address bits.
>>>>> I agree that creating devices on the fly has problems. Another
>>>>> solution is to create one device for each map that is loaded. There
>>>>> would be a couple built-in maps for bundled remotes - each would
>>>>> create a device. Then the user could load more maps with each map
>>>>> creating a device.
>>>> No, please. We currently have already 89 different keymaps in-kernel. Creating
>>>> 89 different interfaces per IR receiver is not useful at all.
>>>>
>>>> IMO, the interfaces should be created as the keymaps are associated
>>>> to an specific IR receiver.
>>> Each IR receiver device driver would have a built-in keymap for the
>>> remote bundled with it. When you load the driver it will poke the
>>> input system and install the map. Any additional keymaps would get
>>> loaded from user space. You would load one keymap per input device.
>>>
>>> You might have 89 maps in the kernel with each map being built into
>>> the device driver for those 89 IR receivers. But you'll only own one
>>> or two of those devices so only one or two of the 89 maps will load.
>>> Building the map for the bundled receiver into the device driver is an
>>> important part of achieving "just works".
>>>
>>> I suspect we'll have a 1,000 maps defined after ten years, most of
>>> these maps will be loaded from user space. But you'll only have two or
>>> three loaded at any one time into your kernel. You need one map per
>>> input device created. These maps are tiny, less than 1KB.
>>>
>>> Having all of these maps is the price of allowing everyone to use any
>>> more that they please. If you force the use of universal remotes most
>>> of the maps can be eliminated.
>> Makes sense. Yet, I would add an option at Kbuild to create a module or not
>> with the bundled IR keymaps.
>>
>> So, it should be possible to have all of them completely on userspace or
>> having them at kernelspace.
> 
> Removing the maps for the bundled remotes from the receiver device
> drivers will break "just works". 

No. This can be provided by an udev application that will load the keytable
when the device is connected.

Of course before adding it into a module, we'll need to write such app.

This will only affects the need of IR during boot time.

> The map will be in an __init section
> of the IR device driver. When it is fed into the input system a RAM
> based structure will be created. 

We can't use __init, since another device needing the keymap may be hot-plugged.

> If you really want the 1KB memory
> back, use sysfs to remove the default map.  An embedded system will
> have a bundled remote so it is going to want the map. 

Yes, but it needs just one map, not all of them. The maps shouldn't be linked
into the drivers, as the same map is used by several different devices on
different drivers. So, the option is to allow customizing the available keymaps,
if CONFIG_EMBEDDED.

Cheers,
Mauro.
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