linux-kernel - Re: [PATCH] Don't probe for DDC on VBE1.2

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Message-Id: <20070215205658.56096f97.akpm@linux-foundation.org>
Date:	Thu, 15 Feb 2007 20:56:58 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Zwane Mwaikambo <zwane@...radead.org>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...e.de>, Tobias Hain <tobias.hain@....de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] Don't probe for DDC on VBE1.2

On Thu, 15 Feb 2007 08:29:49 -0800 (PST) Zwane Mwaikambo <zwane@...radead.org> wrote:

> VBE1.2 doesn't support function 15h (DDC) resulting in a 'hang' whilst
> uncompressing kernel with some video cards. Make sure we check VBE version 
> before fiddling around with DDC.
> 
> http://bugzilla.kernel.org/show_bug.cgi?id=1458
> 
> Opened: 2003-10-30 09:12 Last update: 2007-02-13 22:03
> 
> :(
> 
> Much thanks to Tobias Hain for help in testing and investigating the bug. 
> Tested on;
> 
> i386, Chips & Technologies 65548 VESA VBE 1.2
> CONFIG_VIDEO_SELECT=Y
> CONFIG_FIRMWARE_EDID=Y
> 
> Untested on x86_64.
> 
> Signed-off-by: Zwane Mwaikambo <zwane@...radead.org>
> 
> Index: linux-2.6.20-rc6-mm1/arch/i386/boot/video.S
> ===================================================================
> RCS file: /home/cvsroot/linux-2.6.20-rc6-mm1/arch/i386/boot/video.S,v
> retrieving revision 1.1.1.1
> diff -u -p -B -r1.1.1.1 video.S
> --- linux-2.6.20-rc6-mm1/arch/i386/boot/video.S	30 Jan 2007 05:28:31 -0000	1.1.1.1
> +++ linux-2.6.20-rc6-mm1/arch/i386/boot/video.S	15 Feb 2007 16:27:32 -0000
> @@ -1945,6 +1945,20 @@ store_edid:
>  	rep
>  	stosl
>  
> +	pushw	%es
> +	pushw	%ds
> +	popw	%es
> +	leaw	modelist+1024, %di
> +	movw	$0x4f00, %ax
> +	int	$0x10
> +	popw	%es
> +
> +	cmpw	$0x004f, %ax
> +	jne	no_edid
> +
> +	cmpw	$0x0102, 4(%di)			# only do EDID on > 1.2
> +	je	no_edid
> +
>  	pushw   %es				# save ES
>  	xorw    %di, %di                        # Report Capability
>  	pushw   %di

This makes the long-suffering-but-vigorously-defended Vaio come up with a
black display.  Everything's working OK otherwise.  Sort of a Black Screen
of Life.  I wouldn't call it an improvement though.
-
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