[coreboot] VGA and Graphics

[Igor Skochinsky]

Hello ron,

Wednesday, April 5, 2017, 5:16:33 PM, you wrote:

rm> Zoran, given that we still see _MP_ and even $PIR tables in BIOS,
rm> is it possible that VBT might always be there even if it's not strictly needed?

rm> How do non-EFI kernels get information about video if not via the VBT?

int 10h would be my guess, or possibly that PMInfoBlock VBE3 table. Or
maybe they just load whatever driver matches the PCI ID and let it
handle the details.

rm> On Wed, Apr 5, 2017 at 8:03 AM Zoran Stojsavljevic
rm> <zoran.stojsavljevic at gmail.com> wrote:
rm> To Coreboot,

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

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

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

rm> I'll continue to investigate.

rm> Thank you,
rm> Zoran

rm> On Wed, Apr 5, 2017 at 4:54 PM, Matt DeVillier
rm> <matt.devillier at gmail.com> wrote:
rm> On Tue, Apr 4, 2017 at 10:12 PM, Zoran Stojsavljevic
rm> <zoran.stojsavljevic at gmail.com> wrote:
rm> Hello Matt,

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

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

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

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

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

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

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

rm> Zoran

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


rm> On Tue, Apr 4, 2017 at 2:23 PM, Zoran Stojsavljevic
rm> <zoran.stojsavljevic at gmail.com> wrote:
rm> Furthermore, let me tell you all that this is a mechanism to
rm> support ONLY The Legacy BIOS (UEFI works ONLY with GOP, but this
rm> is another dimension/discussion), and, to all of your knowledge
rm> (which I have no idea how deep it is, I doubt), VBT table survives
rm> postmortem BIOS. By Linux, it will be RELOCATED into much higher
rm> (over 1MB) 32bit protected mode memory (addresses recalculated),
rm> and still use INT10H, using vBIOS (Option ROM, my best guess) down there.


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






-- 
WBR,
 Igor