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            <b><a class="bz_bug_link 
          bz_status_NEEDINFO "
   title="NEEDINFO --- - [SNB, IVB] Page flips hang indefinitely, apparently waiting for mmio writes that never happen"
   href="https://bugs.freedesktop.org/show_bug.cgi?id=75502#c19">Comment # 19</a>
              on <a class="bz_bug_link 
          bz_status_NEEDINFO "
   title="NEEDINFO --- - [SNB, IVB] Page flips hang indefinitely, apparently waiting for mmio writes that never happen"
   href="https://bugs.freedesktop.org/show_bug.cgi?id=75502">bug 75502</a>
              from <span class="vcard"><a class="email" href="mailto:simon@farnz.org.uk" title="Simon Farnsworth <simon@farnz.org.uk>"> <span class="fn">Simon Farnsworth</span></a>
</span></b>
        <pre>I'm still on 3.13.4 here, so backported it as:

diff --git a/drivers/gpu/drm/i915/intel_display.c
b/drivers/gpu/drm/i915/intel_display.c
index d8013f5..66ccf9b 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2300,6 +2300,11 @@ intel_pipe_set_base(struct drm_crtc *crtc, int x, int y,
        struct drm_framebuffer *old_fb;
        int ret;

+        if (intel_crtc_has_pending_flip(crtc)) {
+               DRM_ERROR("pipe is still busy with an old pageflip\n");
+               return -EBUSY;
+        }
+
        /* no fb bound */
        if (!fb) {
                DRM_ERROR("No FB bound\n");

Will let you know the results.</pre>
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