drm/i915: Avoid null dereference if mst_port is unset.

I'm not sure if this is really the case and I don't believe
this is the real fix for the bug mentioned here, but since
I don't see a reliable path when mst_port is set and when
mode_valid is requested I believe it is worth to have this
protection here.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102022
Cc: Elizabeth <elizabethx.de.la.torre.mena@intel.com>
Cc: Stefan Assmann <sassmann@redhat.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20170810145043.24047-1-rodrigo.vivi@intel.com

diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
index 5856855..93fc8ab 100644 (file)
--- a/drivers/gpu/drm/i915/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/intel_dp_mst.c
@@ -370,6 +370,9 @@ intel_dp_mst_mode_valid(struct drm_connector *connector,
        int bpp = 24; /* MST uses fixed bpp */
        int max_rate, mode_rate, max_lanes, max_link_clock;
 
+       if (!intel_dp)
+               return MODE_ERROR;
+
        max_link_clock = intel_dp_max_link_rate(intel_dp);
        max_lanes = intel_dp_max_lane_count(intel_dp);