drm: Use a nondestructive mode for output detect when polling

Destructive load-detection is very expensive and due to failings
elsewhere can trigger system wide stalls of up to 600ms. A simple
first step to correcting this is not to invoke such an expensive
and destructive load-detection operation automatically.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=29536
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=16265
Reported-by: Bruno Prémont <bonbons@linux-vserver.org>
Tested-by: Sitsofe Wheeler <sitsofe@yahoo.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 6 insertions, 6 deletions

diff --git a/drivers/gpu/drm/i915/intel_tv.c b/drivers/gpu/drm/i915/intel_tv.c
index c671f60ce80b..d20b550c0f55 100644
--- a/drivers/gpu/drm/i915/intel_tv.c
+++ b/drivers/gpu/drm/i915/intel_tv.c
@@ -1341,7 +1341,8 @@ static void intel_tv_find_better_format(struct drm_connector *connector)
  * we have a pipe programmed in order to probe the TV.
  */
 static enum drm_connector_status
-intel_tv_detect(struct drm_connector *connector)
+intel_tv_detect(struct drm_connector *connector,
+                bool nondestructive)
 {
         struct drm_display_mode mode;
         struct drm_encoder *encoder = intel_attached_encoder(connector);
@@ -1353,7 +1354,7 @@ intel_tv_detect(struct drm_connector *connector)
 
         if (encoder->crtc && encoder->crtc->enabled) {
                 type = intel_tv_detect_type(intel_tv);
-        } else {
+        } else if (nondestructive) {
                 struct drm_crtc *crtc;
                 int dpms_mode;
 
@@ -1364,10 +1365,9 @@ intel_tv_detect(struct drm_connector *connector)
                         intel_release_load_detect_pipe(&intel_tv->base, connector,
                                                        dpms_mode);
                 } else
-                        type = -1;
-        }
-
-        intel_tv->type = type;
+                        return connector_status_unknown;
+        } else
+                return connector->status;
 
         if (type < 0)
                 return connector_status_disconnected;