Why querying of EDID is limited only to VBE version greater then 2.0?

[Alex Deucher]

On Fri, May 15, 2009 at 1:22 PM, Evgeny M. Zubok <evgeny.zubok at tochka.ru> wrote:
> Alex Deucher <alexdeucher at gmail.com> writes:
>
>>> I have S3 Trio64V2 with VBE 1.2 and I want to add the possibility of
>>> display autodetection via DDC to s3 driver. There is two ways to deal
>>> with DDC: (i) VESA BIOS Extension and (ii) directly from videochip's
>>> DDC registers. The later method currently is impossible to implement
>>> due to the lack of information about DDC registers in accessible
>>> documentation.
>
>> Most of the S3 chips use similar methods for i2c, I'd bet the same
>> registers are used in the virge or savage drivers:
>> http://cgit.freedesktop.org/xorg/driver/xf86-video-s3virge/tree/src/s3v_i2c.c
>> http://cgit.freedesktop.org/xorg/driver/xf86-video-savage/tree/src/savage_i2c.c
>
> I'll try to port this stuff to verify this guess. Although I noticed
> some differences between Virge and TRIOs registers and
> programming. Thanks for idea. The documentation on Virge you sent me
> describes DDC register, but s3.txt for older chips (864, 964, 928, 868,
> 968 an so on) doesn't mention DDC.

The other option would be to execute vbe commands to get the edid and
dump the registers accessed.  this hacked version of vbetool does
exactly that:
http://people.freedesktop.org/~airlied/xresprobe-mjg59-0.4.21.tar.gz

Alex