To Coreboot,

http://www.uefi.org/sites/default/files/resources/UPFS11_P4_UEFI_GOP_AMD.pdf

Please, read about GOP, and what GOP suppose to be.

So, GOP actually need to replace vBIOS, VBT, legacy INT 10H, and complete VBE 3.0 standard. Why (I have no idea what INTEL does with GOP and how it implements it) it is not done in this fashion...?! At least this is my impression how this should be done.

I'll continue to investigate.

Thank you,

Zoran

On Wed, Apr 5, 2017 at 4:54 PM, Matt DeVillier <matt.devillier@gmail.com> wrote:

On Tue, Apr 4, 2017 at 10:12 PM, Zoran Stojsavljevic <zoran.stojsavljevic@gmail.com> wrote:

Hello Matt,

Pretty sure there is NO Option ROM, vBIOS and INT10H. Why INTEL for GOP uses VBT is point of debate. Probably just reduced functionality up to 1280x1024. So they have VBT to support BIOS phase GOP GFX. Only!

From what I can tell, it's mainly used to provide the output connector types/mapping to the GOP driver, as well as level shifting etc.

 

But I am also 100% sure neither GOP, neither VBT survives post BIOS phase. It is out of mind to use VBT for WUXGA, or 1080p, or 4K displays, don't you agree? The detected GFX I/F are passed to Linux as Run Time info (via HOB). Then Linux brings from scratch GFX, using its own, modern I/Fs. And ports appropriate drivers to existing GFX info from HOB.

The VBT data is used by both the Linux and Windows display drivers (via the OpRegion ACPI structure), and the latter will give you a nice black screen if your VBT is missing or incorrectly configured.  As I noted above, it appears to be used more for output/pipe info than display modes (which are all generated from EDID, outside of standard VESA/CEA ones)

On Tue, Apr 4, 2017 at 10:12 PM, Zoran Stojsavljevic <zoran.stojsavljevic@gmail.com> wrote:

Hello Matt,

Pretty sure there is NO Option ROM, vBIOS and INT10H. Why INTEL for GOP uses VBT is point of debate. Probably just reduced functionality up to 1280x1024. So they have VBT to support BIOS phase GOP GFX. Only!

But I am also 100% sure neither GOP, neither VBT survives post BIOS phase. It is out of mind to use VBT for WUXGA, or 1080p, or 4K displays, don't you agree? The detected GFX I/F are passed to Linux as Run Time info (via HOB). Then Linux brings from scratch GFX, using its own, modern I/Fs. And ports appropriate drivers to existing GFX info from HOB.

Zoran

On Tue, Apr 4, 2017 at 11:51 PM, Matt DeVillier <matt.devillier@gmail.com> wrote:

On Tue, Apr 4, 2017 at 2:23 PM, Zoran Stojsavljevic <zoran.stojsavljevic@gmail.com> wrote:

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.

no, the UEFI GOP driver needs the VBT to actually do anything.  Look at any current PC UEFI firmware, or even x86 ChromeOS firmware, and you'll see they all use/contain a VBT still.