AGPGART driver for ArticiaS - ioremap() problem

Benjamin Herrenschmidt benh at
Thu Jan 19 20:59:55 EST 2006

On Thu, 2006-01-19 at 09:50 +0100, Gerhard Pircher wrote:
> > > Hmm, I'm not sure what value agp_bridge->gart_bus_addr should have. The
> > > BIOS doesn't setup it and the VIA AGPGART driver even reads it out from
> > > the northbridge's registers! Where does the value for
> > > agp_bridge->gart_bus_addr come from? For now it is set to 0x0, which
> > > would require the modification in drm_vm.c!?
> > 
> > Well... this is where you AGP aperture will be in bus space.. you'd
> > rather know what to do with it to do a driver...
> I'm afraid so. :)
> > > :) The driver seems to work better with cant_use_aperture set to 1, so
> > > I leave it as it is. BTW: What's the meaning of needs_scratch_page?
> > 
> > Well, set to 1 would mean the aperture isn't accessible on the CPU
> > space. It might seem to work better either because indeed that is the
> > case... or simply because you put it in a wrong place (ie 0 !) There
> > must be a chipset register somewhere that tells you where the aperture
> > is no ?
> I set the AGP aperture base register and agp_bridge->gart_bus_addr to
> 0x01000000 (>=16MB) (trial and error :-) and it seems to work with
> cant_use_aperture=1 

Makes sense, since this value is right in the middle of your RAM :) What
does the firmware sets the base register too ? Can't you try to allocate
some resource in the PCI area that isn't already occupied instead ?

> (and without the modification in drm_vm.c). Even the X
> server maps all the data to this address and displays a login screen.
> Unfortunately it always freezes in. I guess this is due to the missing GART
> flush functionality. So I have to get this working first.

Yah, that would be pretty bad...


More information about the Linuxppc-dev mailing list