PCIe P2P access to GPU memory

[Dirk Eibach]

I want to access GPU VRAM via PCIe P2P access, like DirectGMA but with
mainline drivers.
I can acquire a dmabuf from the GPU and pass it to my PCIe
framegrabber. But I don't see a way to get the PCIe bus address of the
video memory which I need for the P2P transfer. Is there already any
infrastructure in place for doing this? If not, what would be the
right way to implement this? Add another callback to the dmabuf
struct?

Cheers
Dirk