[Linux-fbdev-devel] Re: Who is stomping PCI config space?

[Egbert Eich]

Benjamin Herrenschmidt writes:
 > On Thu, 2005-03-03 at 22:03 -0500, Jon Smirl wrote:
 > > Hopefully someone who knows what is going on with VT switching and how
 > > hardware gets enabled will respond and we can get this fixed in the
 > > server.  I see Zoltan's patch but we shouldn't have to tell X to leave
 > > hardware alone that doesn't belong to it. X just has no business
 > > messing with cards it does not own.
 > > 
 > > Meanwhile I am forced to write to PCI config space and reenable IO
 > > access from inside my interrupt handler. Yuck, yuck, yuck!!!
 > 
 > Well, that shows why we need this arbitration for who gets the VGA
 > enable bits in the kernel :)

It needs to have it in some central place which doesn't necessarily
have to be the kernel. 
The point is: if Jon needs these registers in an interrupt handler
he may have to tweak PCI config space form there anyway since another 
card may currently have VGA routed.

 > 
 > X disables any other VGA card IO/MEM in the system so that at one given
 > point in time, only one of them will decode VGA cycles. Wether it has
 > those cards to drive in it's config or not doesn't matter, the problem
 > at the bus level is the same.

Right. It however should only do so if one of the cards it is driving 
itself requires VGA registers for its mode of operation.

Egbert.