VGA arbitration: API proposal

[Jon Smirl]

The Intel chips appear to have a clean way to totally turn off VGA.

4.1.16 GGC GMCH Graphics Control Register (D0:F0)
(82915G/82915GV/82915GL/82910GL GMCH only)
PCI Device: 0 
Address Offset: 52h 
Default Value: 0030h 
Access: R/W/L Size: 16 bits 

Bit 1 R/W 0b IGD VGA Disable (IVD): 
  0 = Enable. Device 2 (IGD) claims VGA memory and I/O cycles, the
Sub-Class Code within Device 2 Class Code register is 00h.
  1 = Disable. Device 2 (IGD) does not claim VGA cycles (Memory and
I/O), and the Sub-Class Code field within Device 2, Function 0 Class
Code register is 80h.

It even turns off the PCI VGA class mode bit.

I haven't figured out yet how PCI Express routes VGA, but PCI Express
definitely supports VGA since this is from a PCI Express chipset.

-- 
Jon Smirl
jonsmirl at gmail.com