drm/i915: Clear pfit registers when not used by any outputs

... otherwise the panel-fitter may be left enabled with random settings
and cause unintended filtering (i.e. blurring of native modes on external
panels).

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=31942
Reported-and-tested-by: Ben Kohler <bkohler@gmail.com>
Tested-by: Ciprian Docan <docan@eden.rutgers.edu>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 6 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index bee24b1a58e8..255b52ee0091 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -5336,9 +5336,14 @@ static void intel_setup_outputs(struct drm_device *dev)
         struct drm_i915_private *dev_priv = dev->dev_private;
         struct intel_encoder *encoder;
         bool dpd_is_edp = false;
+        bool has_lvds = false;
 
         if (IS_MOBILE(dev) && !IS_I830(dev))
-                intel_lvds_init(dev);
+                has_lvds = intel_lvds_init(dev);
+        if (!has_lvds && !HAS_PCH_SPLIT(dev)) {
+                /* disable the panel fitter on everything but LVDS */
+                I915_WRITE(PFIT_CONTROL, 0);
+        }
 
         if (HAS_PCH_SPLIT(dev)) {
                 dpd_is_edp = intel_dpd_is_edp(dev);