[coreboot] VGA and Graphics

[Igor Skochinsky]

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