linux-kernel - Re: factor out common s2ram wakeup code

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Date:	Tue, 22 Jan 2008 22:24:40 +0100
From:	Pavel Machek <pavel@....cz>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	kernel list <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: factor out common s2ram wakeup code

Hi!

(Lists added back to CC, I dropped them by mistake).

>>>> It seems to compile 32/64bit, and work 32bit... Now, video code should
>>>> be probably shared with kernel/boot; but that was rewritten to C and
>>>> I'm not sure if I know enough about linkers... basically the C code
>>>> should replace mode_set() and friends. Peter, can you help?
>>> Yes, absolutely.  I think we should probably segregate out into a 
>>> subdirectory the part of the code that should be run in 16-bit mode, and 
>>> then it's just a matter of pretty much replicating the mechanisms used in 
>>> arch/x86/boot.
>>
>> I'd basically need second copy of bootup code, placed into page with
>> wakeup_code. I guess I could let gcc compile .c into .s , and then
>> include that... but perhaps there is better way?
>>
>>> How can I best be of help?
>>
>> Teach me how to include .c into wakeup.S. I should be able to figure
>> the rest...
>
> Yes, there is a better way.
>
> The biggest question is if your 16-bit code needs to touch symbols in the 
> 32/64-bit code, or vice versa.  That complicates things a little bit, 
> obviously.

The code is in arch/x86/kernel/acpi/wakeup_32.S
. acpi_copy_wakeup_routine needs to know offsets within 16-bit 
code. I'd like to somehow call code from arch/x86/boot/video*.c
... current version just took (old) .S code, and cut&paste-s it.

> If not, the easiest way is to link the 16-bit code into a separate binary 
> (including both assembly and C code) which can then be included in the 
> kernel proper as a binary blob.  If it *does* need to reference outside 
> symbols, then it needs to be part of the overall link, which means mucking 
> with the top-level link script.
> That's obviously more complex.
>
> Either way, the Makefile bit of this will be a lot easier if we move the 
> 16-bit code into a separate directory.

I only need arch/x86/boot/video*.c ...

> Let me know which way you think makes more sense, and I can send you a 
> framework patch.

I need to access data in that 16-bit code...
									Pavel
-- 
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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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