Thanks for your reply! I need confirm I am understanding your comments
correctly. I think you're suggesting to traverse the pci devices and
check if it owns the I/O port 0x3d4 to detect if the vga device
is initialized. But it seems not be able to resolve the bug. Because
the machine initialization code runs before the generic device
initialization, the I/O port 0x3d4 will not be registered at the time
machine initializes. So it can't change the return value of
pci_vga_init. The return value is checked in ppc code, which causes the
bug.