drm/i915: Really wait for pending flips when panning

drm/i915: Really wait for pending flips when panning

Since obj->pending_flips was never set, intel_pipe_set_base() never
actually waited for pending page flips to complete.

We really do want to wait for the pending flips, because otherwise the
mmio surface base address update could overtake the flip, and you
could end up with an old frame on the screen once the flip really
completes.

Just call intel_crtc_wait_pending_flips() prior to calling
intel_pipe_set_base() instead of calling just intel_finish_fb()
from intel_pipe_set_base(). Moving the call outside of
intel_pipe_set_base() avoids calling it twice from the full
modeset path.

v2: Wait for pending flips w/o holding struct_mutex

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>