[Xorg] The big multiconsole nasty

Egbert Eich eich at pdx.freedesktop.org
Mon Jul 12 05:30:41 PDT 2004

Jesse Barnes writes:
 > On Tuesday, July 6, 2004 9:36 am, Jon Smirl wrote:
 > > --- John Dennis <jdennis at redhat.com> wrote:
 > > > bus topology and that VGA routing is correct. Unlike the current
 > >
 > > You can't make the assumptions about VGA routing. When secondary video
 > > cards are reset by running their ROM, at the very least they enable
 > > their VGA support. Sometimes they remap the bridges too.
 > >
 > > We need kernel support for:
 > > 1) disabling all VGA devices
 > > 2) setting one VGA device active and get the bus routed to it
 > This is possible, but also points out a deficiency in the current X server's 
 > idea of I/O ports.  I spoke with John Dennis about this a few weeks ago, but 
 > it seems to me that we should either:
 >   o make the in/out routines take full pointers for the port address value

This is already done. All addresses in the code are already constructed
by using  base+offset.

 >     - or - 
 >   o pass a PCI tag to them so that the platform code can figure out where to
 >     route the I/O

I also had a similar idea years ago. However I dropped it again:
How about the latencies introduced when each IO operation has to
verify that it is routed correctly?

 > As it stands, the X server's platform code has to assume one, global, I/O port 
 > base address...

Not true any more. Take a look at the AXP and PPC code. Possibly also the 
IA64 code.
On these platforms PIO is 'redirected' to MMIO and each bus has its distinct 
range in the MMIO address space.


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