drm/i915: Don't try to look up object for non-existent fb

crtc->primary->fb may be NULL upon entry to intel_pipe_set_base() if the
primary plane has previously been disabled via the universal plane
interface.  We need to check for NULL before trying to reference
old_fb's obj.

This fixes a regression introduced in

        commit a071fa00647bc9a3c53f917b236fff9aea175e3a
        Author: Daniel Vetter <[email protected]>
        Date:   Wed Jun 18 23:28:09 2014 +0200

        drm/i915: Introduce accurate frontbuffer tracking

Testcase: igt/kms_universal_plane
Cc: Daniel Vetter <[email protected]>
Signed-off-by: Matt Roper <[email protected]>
Reviewed-by: Chris Wilson <[email protected]>
Signed-off-by: Jani Nikula <[email protected]>

0 files changed, 0 insertions, 0 deletions