Re: [Linux-fbdev-devel] Reading the EDID block for x86 machines

[Antonino D. <ad...@po...>]

On Thu, 2003-03-13 at 02:16, Jon Smirl wrote:
> --- Antonino Daplas <ad...@po...> wrote:
> > Unless I missed some imported BIOS calls or other
> > methods to do this or
> > something similar in real-mode...
> 
> You missed something. The address of the VBIOS ROM can
> be controlled by writing to the PCI config space. You
> can make the ROM appear anywhere you want it to.
> 
> This happens even for the boot video device. 
> Somewhere very early in the boot the system BIOS
> enabled the VBIOS ROM and copied it to C000. This is
> the "shadow BIOS" option.
> 

So the steps needed would be:

1.  scan for pci devices looking for the vga controller type

2.  if 1 is found other than the primary, disable the current controller

3.  write to PCI config space of secondary controller the address you
want it to appear (ie C000:0000).  Can I use other addresses?

4. enable the controller

5. far call c000:0003

6. disable the controller

7. repeat

Besides the finer points, did I miss anything obvious?

Tony