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)