On Thu, 19 Apr 2007, Greg KH wrote:
> On Thu, Apr 19, 2007 at 04:11:50PM -0700, Jesse Barnes wrote:
> > On Thursday, April 5, 2007 3:37 pm Adam Jackson wrote:
> > > So I'm attempting to do something fairly heinous (X server across
> > > five video cards), and I hit a fun bug in bridge range setup. See
> > > attached lspci and dmesg, but the short of it is I've got two VGA
> > > chips on one card behind a bridge, which is itself behind a second
> > > PCI bridge, and the bridge ranges get set up so that I can't map the
> > > ROMs, which means I can't post them, and therefore can't use them
> > > period.
Ok, let me start out by saying that at this point in the development cycle
(ie trying to get 2.6.21 out some day), I can't really find it in myself
to care all that deeply about people doing something quote _that_ fairly
heinous ;)
> > > The alignment restriction on the ROMs seems a bit extreme:
> > >
> > > % sudo setpci -s 7:2 ROM_ADDRESS=ffffffff
> > > % sudo setpci -s 7:2 ROM_ADDRESS
> > > f0000001
Yeah, they seem to want 256MB.
> > Yep, looks like those two devices had a problem. Supposedly they want
> > to sit at 256M? Given that we're only giving each bridge 1M of memory
> > space that would definitely be a problem.
We should be sizing the bridge regions by how much space the devices
behind the bridges actually need, BUT I can guess at two problems:
- On PC's, we generally trust any BIOS setup. If the bridge has been
initialized to some value that seems half-way valid we generally leave
it there. Moving things around tends to cause a lot more problems than
it fixes.
- we normally do *not* try to assign ROM resources at all, because a
number of video cards in particular do some really strange stuff with
the ROMS, like share the decoders for the ROM's and the other PCI
resources!
IOW, I think that what happens is that the BIOS has set it up to have a
32MB window, and since the kernel doesn't think there is anything wrong
with that, it leaves it well enough alone.
You could try adding "pci=rom" to the kernel command line, which should
make the kernel try to assign space for the roms too.
I think we used to *never* assign PCI bus resources on x86, but that thing
got fixed some time ago. Now I think we only re-assign them if they were
unassigned *or* if the assignment wasn't working before. But I'm not 100%
sure about that second part... It's been working so well that I don't
think we've had a lot of problems with resource assignment lately, and
I've paged it all out of my brain.
Ivan, can you remind my tired old brain?
Linus
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