[coreboot] VGA and Graphics

[Nico Huber]

On 05.04.2017 17:03, Zoran Stojsavljevic wrote:
> 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.

no, no, no, no. Since VBT is not related to the concept of a Video BIOS
or any standard (how many people does it need to convince you? :-), it
cannot be replaced by something (GOP) that continues this standards
story.

Maybe this helps you to untangle this: When the VBT was invented, it
might have been named after Intel's Video BIOS because that was its
first consumer. However the name is or has become unrelated to its func-
tion. If somebody would come up with a name for the VBT, looking at what
it is today, he might call it Intel Graphics Driver Configuration Table
(IGDT). The acronym IGDT looks much different from VBE, no temptation
to see them related. Also, why should GOP replace IGDT and reinvent how
Intel develops its graphics drivers? GOP is just about pre-OS environ-
ments (cross-vendor), while IGDT is common to all of Intel's graphics
drivers.

>From another perspective: IGDT contains proprietary settings for Intel
silicon, close to register level. VBE is, at its core, about high-level
framebuffer (data in RAM) formats.

Nico

> 
> I'll continue to investigate.
> 
> Thank you,
> Zoran
> 
> On Wed, Apr 5, 2017 at 4:54 PM, Matt DeVillier <matt.devillier at gmail.com>
> wrote:
> 
>> 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.
>>>>
>>>
>>>
>>
> 
> 
>