[Nouveau] [PATCH] drm/ttm: Fix race condition in ttm_bo_delayed_delete

[Luca Barbieri]

> Nvidia cards have a synchronization primitive that could be used to
> synchronize several FIFOs in hardware (AKA semaphores, see [1] for an
> example).

Does this operate wholly on the GPU on all nVidia cards?

It seems that at least on some GPUs this will trigger "software
methods" that are basically a way for the GPU to trigger an interrupt
and stop the FIFO until the CPU handles the interrupt and restarts it.

Also, is there a way on nVidia cards to get interrupts on fences, but
only where the fence sequence number is higher than a dynamically set
value? (so that one could sleep for fence X without getting an
interrupt for every single fence before that)

If not, it could possibly be hacked around by reading from a DMA
object at the address of the fence sequence number and then resizing
the DMA object so that addresses from a certain point on would trigger
a protection fault interrupt.