[Xorg] The big multiconsole nasty

Keith Packard keithp at keithp.com
Fri Jul 2 10:51:12 PDT 2004

Around 18 o'clock on Jul 2, Egbert Eich wrote:

> We have never been able to support multiple ISA video cards.
> However RAC is an importand issue for a lot of PCI (AGP) graphics cards
> at least during initialization.

Ok; I didn't understand the limits of ISA card access; having 
(fortunately) never used a computer with an ISA video card...

And, of course we need some way to touch the VGA I/O ports on arbitrary 
video cards (I believe some S3 cards must be poked in I/O ports before 
they enable MMIO register access).

> It is not only Intel that creates these problems. For many brand new video
> cards the VESA driver is the only option.

Right; you can either use the VESA X driver or the VESA fbdev kernel 
driver.  I mostly wanted to note that even "vendor" drivers can rely on 
the BIOS for mode selection, which is pretty harsh.

> We should not need any PCI remapping if the kernel itself does the right
> mapping.

I thought the problem was that sometimes the kernel can't know what address
range is needed by an arbitrary card -- motherboard and video card bugs
sometimes mean that only a subset of the video memory ends up getting
mapped by the time the X server starts.  Without some way to ask the kernel
to remap things, it wouldn't be possible to fix this safely from user-mode.

> What we may need is an IOCTL to set VGA routing on bridges. 

I'd sure rather see the X server not need to understand the whole PCI bus 


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