Quoting Thierry Reding (2018-01-11 22:22:46)

From: Thierry Reding <redacted>

This set of patches adds support for fences to Tegra DRM and complements
the fence FD support for Nouveau. Technically this isn't necessary for a
fence-based synchronization loop with Nouveau because the KMS core takes
care of all that, but engines behind host1x can use the IOCTL extensions
provided here to emit fence FDs that in turn can be used to synchronize
their jobs with either the scanout engine or the GPU.

Whilst hooking up fences, I advise you to also hook up drm_syncobj.
Internally they each resolve to another fence, so the mechanics are
identical, you just need another array in the uABI for in/out syncobj.
The advantage of drm_syncobj is that userspace can track internal fences
using inexhaustible handles, reserving the precious fd for IPC or KMS.
-Chris