[coreboot] VGA and Graphics

[Nico Huber]

Hi Ron,

On 04.04.2017 19:46, ron minnich wrote:
> Igor, if you are going to say things like "AFAIK there is no public
> description of these tables' layout and contents, only Intel knows how to
> build and parse them.", it's really a good idea to back it up with a
> primary source, especially since you also use phrases like "I assume" and
> "I guess". I am pretty sure you're wrong in this case. The V in VBT, as I
> understand it, means VESA, and VESA has been a standard for about 30 years.
> 
> Please, everyone, if you're going to move this conversation forward, you
> need to cite primary sources at least, such as this one:
> http://www.petesqbsite.com/sections/tutorials/tuts/vbe3.pdf.

now you got confused too. I'll try to clarify.

VBE means VESA (Video Electronics Standards Association) BIOS Extension.
It's a Video BIOS interface extension (i.e. specifying additional BIOS
calls). Don't know if it was public from the beginning (you often have
to be a VESA member to get access to their "standards"), but the inter-
face is used by many open source programs. It's vendor independent. Also
it's off-topic, nobody was discussing it here.

As Igor noted, VBE has absolutely nothing to do with VBT.

VBT means Video BIOS Table. It's a 100% Intel specific table of confi-
guration options for Intel's Video BIOS and Intel's graphics drivers.
There is no public documentation, but as it's used by the Linux driver,
at least the structure and some of the values are publicly "documented"
[1]. Developers of the i915 Linux driver stated that they are not wil-
ling to support systems without a VBT. Most features of the i915 driver
work without a VBT by chance. But anything board specific, like inte-
grated panels in laptops, will likely _not_ work. I'd also expect that
they won't count it as a regression if something breaks but would still
work with a VBT. (Windows won't even try to get things running without
VBT, AFAIK.)

An OEM should have access to Intel's binary configuration tool and the
specification file for the VBT of his processor's generation. It comes
along with the VBIOS, I suppose.

Nico

PS. Igor, Zoran please write text-only emails or at least make sure the
    text version is readable and quotes are visible as quotes.

[1]
https://www.kernel.org/doc/html/latest/gpu/i915.html#video-bios-table-vbt