[coreboot] VGA and Graphics

[Matt DeVillier]

On Tue, Apr 4, 2017 at 10:12 PM, Zoran Stojsavljevic <
zoran.stojsavljevic at 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 at 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 at gmail.com>
> wrote:
>
>>
>>
>> On Tue, Apr 4, 2017 at 2:23 PM, Zoran Stojsavljevic <
>> zoran.stojsavljevic at 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.
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.coreboot.org/pipermail/coreboot/attachments/20170405/44929a8e/attachment.html>