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, 1 deletions

diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
index 4b7735196cd5..0350e5d711f8 100644
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -400,7 +400,9 @@ intel_crt_load_detect(struct drm_crtc *crtc, struct intel_encoder *intel_encoder
         return status;
 }
 
-static enum drm_connector_status intel_crt_detect(struct drm_connector *connector)
+static enum drm_connector_status
+intel_crt_detect(struct drm_connector *connector,
+                 bool nondestructive)
 {
         struct drm_device *dev = connector->dev;
         struct drm_encoder *encoder = intel_attached_encoder(connector);
@@ -419,6 +421,9 @@ static enum drm_connector_status intel_crt_detect(struct drm_connector *connecto
         if (intel_crt_detect_ddc(encoder))
                 return connector_status_connected;
 
+        if (nondestructive)
+                return connector->status;
+
         /* for pre-945g platforms use load detect */
         if (encoder->crtc && encoder->crtc->enabled) {
                 status = intel_crt_load_detect(encoder->crtc, intel_encoder);