[coreboot] VGA and Graphics

Wed Apr 5 20:46:58 CEST 2017

Man, I did not know that my picking on Legacy vBIOS, VBT, and legacy
mechanisms will make such a noise. And so many responses.

I should say, I am glad that I provoked such an avalanche of info, since, I
have to say, I am learning a lot reading this email thread. I hope others
learn a lot too. And... We all are trying to connect missing puzzles. I
certainly do (and pass to you what I do know - NOT always the case)!

I just came back from BBALL, and I am pretty dead, as dead cat's last
jump... It was tough on my body (3:3 on full real court, two hoops, 2
hours)... I'll try reasonably to reply to these emails! :-(

> Intel provides a binary-only GOP driver (IntelGopDriver.efi) to OEMs who
> embed it into their UEFI implementations. I don't know if it itself requires
VBT.

Igor,

In present BIOSes (most of them are 64b, thus UEFI), as I understand, there
are three modes of operations:
[1] Legacy only (CSM ON);
[2] Combined mode (have no idea how this does work);
[3] True UEFI (CSM OFF)!

Now, I never use/used mode [2]. I am NOT fan of mixing these modes. I use
[1] if I must too, but my preferred mode is [3].

Regarding these two modes,:
[1] Legacy - does use vBIOS (maximum size 64KB), INT 10H, VBT, and all this
is inherited by OS.
[3] UEFI - does use GOP driver (MORE that 64KB in size, there is no such a
limit as for vBIOS).

These are The Facts. Matt (De Viller) can beat me with the baseball bat,
but this I know, this is in concrete. I would NOT change (about what I
wrote here above) my opinion.

It seems that, after GOP dies, still, orphaned VBT survives post mortem
UEFI (as part of UEFI run time data passed to OS).

I (here, Matt makes me doubtful, and I will thank him for that) always was
naive and thought that VBT is NOT part of GOP driver. But, apparently, I
might be mistaken, and Matt (De Viller) is probably right.

Now... The bloody name VBT is one which confuses me: Video BIOS Table
(VBT). This is my problem, but, if I better think, maybe INTEL CCG/OTC pros
wanted just to continue to inherit the transparency. About what I think,
about VBT, I'll reply to Matt (DaEmon) and Coreboot himself. ;-)

I am glad that I missed some points. :-)

Zoran

On Wed, Apr 5, 2017 at 7:59 PM, Igor Skochinsky via coreboot <
coreboot at coreboot.org> wrote:

> Hello Zoran,
>
> Wednesday, April 5, 2017, 5:03:33 PM, you wrote:
>
> ZS> To Coreboot,
>
> ZS> http://www.uefi.org/sites/default/files/resources/
> UPFS11_P4_UEFI_GOP_AMD.pdf
>
> ZS> Please, read about GOP, and what GOP suppose to be.
>
> ZS> So, GOP actually need to replace vBIOS, VBT, legacy INT 10H, and
> ZS> complete VBE 3.0 standard. Why (I have no idea what INTEL does
> ZS> with GOP and how it implements it) it is not done in this
> ZS> fashion...?! At least this is my impression how this should be done.
>
> Well, yes, the GOP is used in UEFI for video output (e.g. in the UEFI
> shell or the BIOS setup screens) and in theory any OS can use it to
> access video after boot although I don't know any OS that does; at
> least both Linux and Windows use their own drivers which talk to the
> hardware directly (and those drivers seem to require VBT currently).
> Though I think the Windows bootloader (winload.efi) can use GOP to
> display the boot menu.
>
> Intel provides a binary-only GOP driver (IntelGopDriver.efi) to OEMs who
> embed it into their UEFI implementations. I don't know if it itself
> requires VBT.
>
>
> ZS> I'll continue to investigate.
>
> ZS> Thank you,
> ZS> Zoran
>
> ZS> On Wed, Apr 5, 2017 at 4:54 PM, Matt DeVillier
> ZS> <matt.devillier at gmail.com> wrote:
> ZS> On Tue, Apr 4, 2017 at 10:12 PM, Zoran Stojsavljevic
> ZS> <zoran.stojsavljevic at gmail.com> wrote:
> ZS> Hello Matt,
>
> ZS> Pretty sure there is NO Option ROM, vBIOS and INT10H. Why INTEL
> ZS> for GOP uses VBT is point of debate. Probably just reduced
> ZS> functionality up to 1280x1024. So they have VBT to support BIOS phase
> GOP GFX. Only!
>
> ZS> From what I can tell, it's mainly used to provide the output
> ZS> connector types/mapping to the GOP driver, as well as level shifting
> etc.
> ZS>
>
> ZS> But I am also 100% sure neither GOP, neither VBT survives post
> ZS> BIOS phase. It is out of mind to use VBT for WUXGA, or 1080p, or
> ZS> 4K displays, don't you agree? The detected GFX I/F are passed to
> ZS> Linux as Run Time info (via HOB). Then Linux brings from scratch
> ZS> GFX, using its own, modern I/Fs. And ports appropriate drivers to
> existing GFX info from HOB.
>
> ZS> The VBT data is used by both the Linux and Windows display
> ZS> drivers (via the OpRegion ACPI structure), and the latter will
> ZS> give you a nice black screen if your VBT is missing or incorrectly
> ZS> configured.  As I noted above, it appears to be used more for
> ZS> output/pipe info than display modes (which are all generated from
> ZS> EDID, outside of standard VESA/CEA ones)
>
> ZS> On Tue, Apr 4, 2017 at 10:12 PM, Zoran Stojsavljevic
> ZS> <zoran.stojsavljevic at gmail.com> wrote:
> ZS> Hello Matt,
>
> ZS> Pretty sure there is NO Option ROM, vBIOS and INT10H. Why INTEL
> ZS> for GOP uses VBT is point of debate. Probably just reduced
> ZS> functionality up to 1280x1024. So they have VBT to support BIOS phase
> GOP GFX. Only!
>
> ZS> But I am also 100% sure neither GOP, neither VBT survives post
> ZS> BIOS phase. It is out of mind to use VBT for WUXGA, or 1080p, or
> ZS> 4K displays, don't you agree? The detected GFX I/F are passed to
> ZS> Linux as Run Time info (via HOB). Then Linux brings from scratch
> ZS> GFX, using its own, modern I/Fs. And ports appropriate drivers to
> existing GFX info from HOB.
>
> ZS> Zoran
>
> ZS> On Tue, Apr 4, 2017 at 11:51 PM, Matt DeVillier
> ZS> <matt.devillier at gmail.com> wrote:
>
>
> ZS> On Tue, Apr 4, 2017 at 2:23 PM, Zoran Stojsavljevic
> ZS> <zoran.stojsavljevic at gmail.com> wrote:
> ZS> Furthermore, let me tell you all that this is a mechanism to
> ZS> support ONLY The Legacy BIOS (UEFI works ONLY with GOP, but this
> ZS> is another dimension/discussion), and, to all of your knowledge
> ZS> (which I have no idea how deep it is, I doubt), VBT table survives
> ZS> postmortem BIOS. By Linux, it will be RELOCATED into much higher
> ZS> (over 1MB) 32bit protected mode memory (addresses recalculated),
> ZS> and still use INT10H, using vBIOS (Option ROM, my best guess) down
> there.
>
>
> ZS> no, the UEFI GOP driver needs the VBT to actually do anything.
> ZS> Look at any current PC UEFI firmware, or even x86 ChromeOS
> ZS> firmware, and you'll see they all use/contain a VBT still.
>
>
>
>
> --
> WBR,
>  Igor                            mailto:skochinsky at mail.ru
>
>
> --
> coreboot mailing list: coreboot at coreboot.org
> https://www.coreboot.org/mailman/listinfo/coreboot
>
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