[Bug 90128] New: Big monitor has blank display (HDMI or DVI) in any kernel since and including 3.13 (despite earlier fixes)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=90128

            Bug ID: 90128
           Summary: Big monitor has blank display (HDMI or DVI) in any
                    kernel since and including 3.13 (despite earlier
                    fixes)
           Product: DRI
           Version: XOrg git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: philipmorant at gmail.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

My 2560x1440 WQHD monitor works find under linux kernel 3.11 and 3.12 but shows
nothing but a blank screen under 3.13 and later kernels.  It's a haswell system
running on a Z97.  I have one other monitor connected, over DSUB, at 1920x1080
pixels.

The monitor accepts only dual dvi inputs.  I tried lowering the portclock by
specifying refresh rates of 30Hz and lower, and while xrandr reported the
monitor working with that, nothing appeared onscreen.  This monitor seems fussy
about its refresh rates.

After reading other issues and setting drm.debug=0xe I discovered that the
following patch to intel_hdmi.c fixes the problem for me:
@@ -849,7 +849,7 @@ static int hdmi_portclock_limit(struct intel_hdmi *hdmi,
bool respect_dvi_limit)
{
    struct drm_device *dev = intel_hdmi_to_dev(hdmi);

-   if ((respect_dvi_limit && !hdmi->has_hdmi_sink) || IS_G4X(dev))
+   if (IS_G4X(dev))
       return 165000;
    else if (IS_HASWELL(dev) || INTEL_INFO(dev)->gen >= 8)
       return 300000;

Of course the ! hdmi->has_hdmi_sink check is in there for a reason, and
maintainers may not consider my patch to be a fix at all.  All I can say is, it
makes my monitor work.  Happy day.



*Possibly* related issues:
https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/1215449

Definitely relevant:
https://bbs.archlinux.org/viewtopic.php?id=179120

This fix should have resolved the issue for me, but didn't:
https://bugzilla.kernel.org/show_bug.cgi?id=72961

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