linux-kernel - Re: [PATCH] retrieve VBE EDID/DDC info independent of used video mode

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Date:	Thu, 02 Aug 2007 18:16:46 +0800
From:	"Antonino A. Daplas" <adaplas@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Daniel Drake <dsd@...too.org>,
	Zwane Mwaikambo <zwane@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Beulich <jbeulich@...ell.com>,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...e.de>
Subject: Re: [PATCH] retrieve VBE EDID/DDC info independent of used video
 mode

H. Peter Anvin wrote:
> Antonino A. Daplas wrote:
>> On Wed, 2007-08-01 at 09:54 +0800, Antonino A. Daplas wrote:
>>> On Tue, 2007-07-31 at 21:17 -0400, Daniel Drake wrote:
>>>> Zwane Mwaikambo wrote:
>>>>> Sorry if this has been hashed out before, but could you point me
>>>>> towards the gentoo bugzilla entry? I'm trying to understand how
>>>>> your setup broke. Which version VBE does your system have?
>>>> Here's the bug:
>>>> http://bugs.gentoo.org/show_bug.cgi?id=181067
>>>>
>>> Looking at the dmesg output of the working and failing kernel, it does
>>> seem that there's no EDID block available in the failing kernel.
>>>
>>
>> BTW, I looked at the above bug report, it seems his last dmesg does not
>> have fbcon enabled.  Make sure that CONFIG_FRAMEBUFFER_CONSOLE=y before
>> doing more tests (the problem of lack of the EDID block in the failing
>> kernel still applies).
>>
> 
> Okay, I'm royally puzzled why that would be.  I've gone over the code
> quite a few times, and I do not see any way (other than VESA < 2.0) that
> could cause that.
> 
> I look forward to getting the debug output; depending on what it is we
> might have to get some debugging output from the setup code.
> 
> We can printf in the new setup code, although obviously that requires
> leaving the screen in text mode.  However, EDID information should still
> be available.
> 
 
How about this patch?

Tony
---

Subject: video setup: Fix VBE DDC reading

Add memory operand constraint and write-only modifier to the inline
assembly to effect the writing of the EDID block to boot_params.edid_info.

Signed-off-by: Antonino Daplas <adaplas@...il.com>
---

 arch/i386/boot/video-vesa.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/i386/boot/video-vesa.c b/arch/i386/boot/video-vesa.c
index e6aa9eb..f1bc71e 100644
--- a/arch/i386/boot/video-vesa.c
+++ b/arch/i386/boot/video-vesa.c
@@ -268,7 +268,7 @@ #ifdef CONFIG_FIRMWARE_EDID
 	dx = 0;			/* EDID block number */
 	di =(size_t) &boot_params.edid_info; /* (ES:)Pointer to block */
 	asm(INT10
-	    : "+a" (ax), "+b" (bx), "+d" (dx)
+	    : "+a" (ax), "+b" (bx), "+d" (dx), "=m" (boot_params.edid_info)
 	    : "c" (cx), "D" (di)
 	    : "esi");
 #endif /* CONFIG_FIRMWARE_EDID */

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