[Open-graphics] From PCI to VGA registers

[Mark]

Anton Soppelsa wrote:
>> > * From the discussion going on here, it looks like initialising the
>> > video card is not straightforward at all. Is a PCI VGA card more
>> > difficult to set up that any other types of PCI cards?
>>   
> It's totally straightforward, if you have proper documentation.  The
> VGA BIOS, also, is just code in ROM that the CPU executes.  It is
> called from the system BIOS at an appropriate time.  VGA is only made
> complex by the fact that PC BIOS and software assume certain specific
> capabilities of the graphics card.
> 
Does the PC BIOS expect anything *besides* 80x25 text mode?  What's the 
minimal set of expectations the PC BIOS has of the graphics card?

Let me guess: it's not standard, right? ;)  I'm thinking of PC BIOSes 
that give a splash screen during POST, for instance.

What's a reasonable minimum, then?