This
register is programmed to a value that falls within the AGP area (as
defined by RADEON_MC_AGP_LOCATION) if I understand the code correctly.
My understanding is that AGP only does transfers system RAM -> video RAM
and all transfers in the opposite direction have to use plain PCI
transfers at least as far as the bus is concerned.
You mean system RAM -> graphics card, right? Does this mean that the
graphics card cannot always write into memory that falls within
RADEON_MC_AGP_LOCATION?
I don't think we can rely on this.
My understanding is that dev->agp->base is the address where the AGP GART
mirrors the pieces of system RAM comprising AGP space.
Yes, that's my understanding, too. But what is the Radeon's business knowing
that address? Why does it need to know this address? I thought this was CPU
address space, not card address space.
Yes, however it is convenient to do so.
The point is that AGP base address will not normally overlap the location
of system RAM. This is, of course, only reasonable for 32 bit systems..
best
Vladimir Dergachev
cu,
Nicolai
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