Created attachment 96206 [details] [review]
RFC patch on top of 34d59508 (drm/nouveau: fix TTM_PL_TT memtype on pre-nv50)

Commit 0a0afd28 (drm/nv50-/disp: move DP link training to core and
train from supervisor) removed a call to 'nouveau_dp_dpms' at the
bottom of nv50_display.c.

Without this call, 'xset dpms force {on,off}' does not have any effect
on my DP-attached monitor.

The attached proof-of-concept patch re-adds the call, as well as a partial
version of nouveau_dp_dpms which causes 'force off' to work again.

It is not clear to me how to trigger link training in the supervisor,
so nouveau_dp_dpms skips that step when handling DRM_MODE_DPMS_ON.
The result is that 'force on' does not cause the monitor to wake up,
and the connection is effectively dead.

Could somebody familiar with the driver could comment on the next
steps to undertake to restore the full {on,off} functionality?