linux-kernel - Re: [RFC] Should we create a raw input interface for IR's ? - Was: Re: [PATCH 1/3 v2] lirc core device driver infrastructure

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Message-ID: <4B10FC0A.7050408@s5r6.in-berlin.de>
Date:	Sat, 28 Nov 2009 11:31:38 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Mauro Carvalho Chehab <mchehab@...hat.com>
CC:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Krzysztof Halasa <khc@...waw.pl>,
	Jarod Wilson <jarod@...hat.com>, linux-kernel@...r.kernel.org,
	Mario Limonciello <superm1@...ntu.com>,
	linux-input@...r.kernel.org, linux-media@...r.kernel.org,
	Janne Grunau <j@...nau.net>,
	Christoph Bartelmus <lirc@...telmus.de>
Subject: Re: [RFC] Should we create a raw input interface for IR's ? - Was:
 Re: [PATCH 1/3 v2] lirc core device driver infrastructure

Mauro Carvalho Chehab wrote:
> Dmitry Torokhov wrote:
[scancode-to-keycode map size]
>> Hmm, why can't you just resize it when you get EVIOCSKEYCODE for
>> scancode that would be out of bounds for the current table (if using
>> table approach)?
[...]
> Let's suppose, for example that instead of using a 49 keys
> IR, they want to use some programable IR with 55 keys, with different
> scancodes. This means that they'll need to delete all 49 scancodes from the old IR 
> and add 55 new scancodes. As there's no explicit call to delete a scan code, the solution
> I found with the current API is to read the current scancode table and replace them with
> KEY_UNKNOWN, allowing its re-use (this is what the driver currently does) or deleting
> that scancode from the table. After deleting 49 keys, you'll need to add the 55 new keys.
> If we do dynamic table resize for each operation, we'll do 104 sequences of kmalloc/kfree
> for replacing one table.

It is not a performance sensitive task, is it?  If you can trade ABI
simplicity for performance (which shouldn't actually matter), that'd be
a better deal.

Besides, some of the necessary kernel-internal house-keeping can also be
deferred until close().

> IMO, it would be better to have an ioctl to do the keycode table resize. An optional flag
> at the ioctl (or a separate one) can be used to ask the driver to clean the current
> keymap table and allocate a new one with the specified size. 
> This will avoid playing with memory allocation for every new key and will provide a simple
> way to say to the driver to discard the current keybable, since a new one will be used.

OTOH, an additional "forget all current mappings" ioctl sounds like an
ABI simplification.
-- 
Stefan Richter
-=====-==--= =-== ===--
http://arcgraph.de/sr/
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