If we start disabling the encoders, there is a potential for a pending
flip to never occur - and so we will end up waiting indefinitely.

v2: Also pre-emptively perform the drm_vblank_off() before switching off
the encoders.

References: 
https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/1097315
Cc: Timo Aaltonen <[email protected]>
Cc: Daniel Vetter <[email protected]>
Signed-off-by: Chris Wilson <[email protected]>
---
 drivers/gpu/drm/i915/intel_display.c |   17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c 
b/drivers/gpu/drm/i915/intel_display.c
index da1ad9c..15cc838 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -3486,15 +3486,15 @@ static void ironlake_crtc_disable(struct drm_crtc *crtc)
        int plane = intel_crtc->plane;
        u32 reg, temp;
 
-
        if (!intel_crtc->active)
                return;
 
+       intel_crtc_wait_for_pending_flips(crtc);
+       drm_vblank_off(dev, pipe);
+
        for_each_encoder_on_crtc(dev, crtc, encoder)
                encoder->disable(encoder);
 
-       intel_crtc_wait_for_pending_flips(crtc);
-       drm_vblank_off(dev, pipe);
        intel_crtc_update_cursor(crtc, false);
 
        intel_disable_plane(dev_priv, plane, pipe);
@@ -3570,13 +3570,14 @@ static void haswell_crtc_disable(struct drm_crtc *crtc)
        if (!intel_crtc->active)
                return;
 
+       intel_crtc_wait_for_pending_flips(crtc);
+       drm_vblank_off(dev, pipe);
+
        is_pch_port = haswell_crtc_driving_pch(crtc);
 
        for_each_encoder_on_crtc(dev, crtc, encoder)
                encoder->disable(encoder);
 
-       intel_crtc_wait_for_pending_flips(crtc);
-       drm_vblank_off(dev, pipe);
        intel_crtc_update_cursor(crtc, false);
 
        intel_disable_plane(dev_priv, plane, pipe);
@@ -3687,16 +3688,16 @@ static void i9xx_crtc_disable(struct drm_crtc *crtc)
        int pipe = intel_crtc->pipe;
        int plane = intel_crtc->plane;
 
-
        if (!intel_crtc->active)
                return;
 
+       intel_crtc_wait_for_pending_flips(crtc);
+       drm_vblank_off(dev, pipe);
+
        for_each_encoder_on_crtc(dev, crtc, encoder)
                encoder->disable(encoder);
 
        /* Give the overlay scaler a chance to disable if it's on this pipe */
-       intel_crtc_wait_for_pending_flips(crtc);
-       drm_vblank_off(dev, pipe);
        intel_crtc_dpms_overlay(intel_crtc, false);
        intel_crtc_update_cursor(crtc, false);
 
-- 
1.7.10.4

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