[coreboot] VGA and Graphics

[ron minnich]

These are great corrections! Thanks everyone, sorry for my confusion.

The information I'm seeing here is really useful, would somebody consider
putting it on the wiki? Among other things, it would reduce my own levels
of confusion.

ron

On Tue, Apr 4, 2017 at 12:23 PM Zoran Stojsavljevic <
zoran.stojsavljevic at gmail.com> wrote:

> Wait a moment, Ron... :-)
>
> Igor is in some points correct. But I need to digest document, you've
> attached, much more in details. I recall some interesting things, reading
> this document, while reading some (jumping around) context.
>
> Very interesting discussion it is, although BIOS is associated with vBIOS
> and VBT in Option ROMs. I need to digest more about these data, you have
> presented, Ron.
>
> VBT stands for Video BIOS Table, VBE is VESA BIOS Extension. I am very
> sure these two things have very much to do with each other, since I can
> imagine that modes (described in VBE 3.0, are supported exactly by VBT,
> which needs to translate VBE modes to some Video timings, and video HSync,
> VSync, Back Porch, Front Porch, blanking dot and line intervals... Low
> Level GFX, which is not too much known to vast majority of the people.
>
> I would like all to look into the document
> http://www.petesqbsite.com/sections/tutorials/tuts/vbe3.pdf, page 19.
> These are the modes VBE 3.0 supports.
>
> Furthermore, let me tell you all that this is a mechanism to support ONLY
> The Legacy BIOS (UEFI works ONLY with GOP, but this is another
> dimension/discussion), and, to all of your knowledge (which I have no idea
> how deep it is, I doubt), VBT table survives postmortem BIOS. By Linux, it
> will be RELOCATED into much higher (over 1MB) 32bit protected mode memory
> (addresses recalculated), and still use INT10H, using vBIOS (Option ROM, my
> best guess) down there.
>
> I would not draw so fast... As many of you do! ;-)
>
> Thank you,
> Zoran
>
> On Tue, Apr 4, 2017 at 7:46 PM, ron minnich <rminnich at gmail.com> 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.
>
>
> thanks
>
> ron
>
> On Tue, Apr 4, 2017 at 10:19 AM Igor Skochinsky via coreboot <
> coreboot at coreboot.org> wrote:
>
> Hello Zoran,
>
>
> Monday, April 3, 2017, 8:58:43 PM, you wrote:
>
>
>
> VBT should fulfill this VBE standard, as my best understanding is, or not?!
>
> VBE only describes the int 10h BIOS interface extensions, VBT are tables
> used by Intel to provide info about how to control the GPU (I assume).
> AFAIK there is no public description of these tables' layout and contents,
> only Intel knows how to build and parse them.
> Both VBE(code) and VBT (data) may be present in the video card's option
> ROM, I guess that's the only common part.
>
>
>
>
> Zoran
>
> On Mon, Apr 3, 2017 at 7:36 PM, Igor Skochinsky via coreboot <
> coreboot at coreboot.org> wrote:
> Hello Zoran,
>
> Monday, April 3, 2017, 9:24:41 AM, you wrote:
>
>
> > *VBT is not code, it's a table* -- that's what the T is -- and you can
> create it any way you want.
>
> Not going to say more, anyway. Just to point to the standard:
> https://en.wikipedia.org/wiki/
> <https://en.wikipedia.org/wiki/VESA_BIOS_Extensions>VESA_BIOS_Extensions
> <https://en.wikipedia.org/wiki/VESA_BIOS_Extensions>
>
>
> Not sure why you posted this link. VBE is not VBT, it's a completely
> separate and different thing.
>
>
>
>
>
> To clever enough! ;-)
>
> Zoran
>
> On Mon, Apr 3, 2017 at 2:38 AM, ron minnich <rminnich at gmail.com> wrote:
> As for graphics startup, here's what I learned when I was doing this in
> 2012/2013: the kernel could start sandy and ivy with no vbios needed.
> However, I have been told that the veil of secrecy has started to draw a
> bit closer in subsequent chipsets, and that something like a VGA BIOS/GOP
> has to run or graphics will not work. I really don't know, I have not
> looked at this in over 3 years.
>
> Todd, just to make sure we're on the same page, VBT is not code, it's a
> table -- that's what the T is -- and you can create it any way you want.
>
> Also, as for numbers: the fastest graphics startup, by far, was when we
> had coreboot- based startup with configuration specialized to the chromeos
> laptop. How fast? At one point we had a pixel booting to chromeos prompt in
> 2.7 seconds, reduced from 7.7 seconds when linux did the graphics init.
> We've seen that the linux graphics init is highly concurrent and
> generalized, and that tends to mean slow. Of course this was all far faster
> than the 8086-mode vga BIOS supplied by "the vendor". But we were a bit
> surprised to see how much faster coreboot was than the linux kernel.
>
> I doubt this speed difference matters any more, since boot time only needs
> to be "fast enough" nowadays and 10 seconds seems to do it for most people
> -- plus, any 5-second advantage in boot time vanishes as soon as you go to
> your first web page.
>
> ron
>
>
>
> On Sun, Apr 2, 2017 at 5:31 PM ron minnich <rminnich at gmail.com> wrote:
> So, I'll mention go userland one last time, for a simple reason: I have it
> on good authority that at some places, saying you have a go userland
> instead of a c userland checks a check box on a security checklist. I think
> that's a sensible decision, having watched all the awful ways that C
> programs tend to go wrong :-)
>
> ron
>
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> *--  WBR,  Igor *--
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