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

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Message-ID: <4B1D9714.5060000@redhat.com>
Date:	Mon, 07 Dec 2009 22:00:20 -0200
From:	Mauro Carvalho Chehab <mchehab@...hat.com>
To:	Krzysztof Halasa <khc@...waw.pl>
CC:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Gerd Hoffmann <kraxel@...hat.com>,
	Jarod Wilson <jarod@...sonet.com>,
	Christoph Bartelmus <lirc@...telmus.de>, awalls@...ix.net,
	j@...nau.net, jarod@...hat.com, jonsmirl@...il.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?

Krzysztof Halasa wrote:
> Mauro Carvalho Chehab <mchehab@...hat.com> writes:
> 

>> struct input_keytable_entry {
>>  	u16	index;
>>  	u64	scancode;
>>  	u32	keycode;
>> } __attribute__ ((packed));
>>
>> (the attribute packed avoids needing a compat for 64 bits)
> 
> Maybe { u64 scancode; u32 keycode; u16 index; u16 reserved } would be a
> bit better, no alignment problems and we could eventually change
> "reserved" into something useful.
> 
> But I think, if we are going to redesign it, we better use scancodes of
> arbitrary length (e.g. protocol-dependent length). It should be opaque
> except for the protocol handler.

Yes, an opaque type for scancode at the userspace API can be better, but
passing a pointer to kernel will require some compat32 logic (as pointer
size is different on 32 and 64 bits).

We may use something like an u8[] with an arbitrary large number of bytes.
In this case, we need to take some care to avoid LSB/MSB troubles.

Cheers,
Mauro.
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