Dave Jones wrote:
2. 'The in-kernel AGPGART doesn't have all the features our driver requires'.
Newsflash: I take patches.
Sifting through the ATI mashed-up agpgart is quite painful, as there are so many changes in there ifdef'd to hell and back that its hard to see whats really needed and what isn't. So, lets talk. Tell me what you need from the kernel GART driver. If it makes sense, I'll merge patches in a heartbeat.
(I'm about to show total ignorance of how agpgart works. Beware!)
One problem I've always had with AGP support on Linux is that when you have a 256MB aperture, that consumes 256MB of physical memory, whether it's being actively used or not. In the future, it would be nice if drivers that use AGP could do something more dynamic. At the very least, not having physical pages backing part of the aperture until needed would be great.
Ideally a driver could say, "I want this page to back this part of the aperture." That would make things like APPLE_client_storage or ARB_vertex_buffer_objects truly zero-copy. In fact, I think that's how it works on OS X. I seem to recall some discussions a few years ago about why this is difficult on x86, but I don't remember the reasons. I can still dream. :)
This sort of stuff motivated the design of the agpgart interface from the beginnning. It was an attempt to allow every possible perversion of this idea, as proposed/demanded by various vendors, that led to the quite complex interface that agpgart ended up with. (For some reason I remember XiG as being one of the most strident...) Some irony then that most vendors end up not using it, and that the opensource drivers don't make use of the complexities of the interface...
In other words, I'm pretty sure agpgart can do this stuff already - you just need to wrap your mind around the interface.
Keith
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