[Bug 68485] New: triple monitor support not working on HD 4600

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=68485

          Priority: medium
            Bug ID: 68485
          Assignee: chris at chris-wilson.co.uk
           Summary: triple monitor support not working on HD 4600
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: xorg at richardneill.org
          Hardware: x86-64 (AMD64)
            Status: NEW
           Version: git
         Component: Driver/intel
           Product: xorg

Created attachment 84538
  --> https://bugs.freedesktop.org/attachment.cgi?id=84538&action=edit
Xorg logfile

I have a Gigabyte GA-H87N-wifi motherboard, which explicitly supports 3
monitors at the same time from the motherboards' onboard graphics (2x HDMI, 1x
DVI). The CPU is an Intel 4570S with HD4600 graphics (also supporting 3 heads
at the same time). However, I can only get 2 monitors (any 2, but not all 3)
working. All monitors are identical 1600x1200 (NEC LCD2070NX).

The KDE systemsettings GUI helpfully shows icons for all 3 monitors, but one is
always greyed out, and attempting to enable it emits "Failed to set mode:
Invalid argument" in Xorg.0.log. Xrandr compians "Configure crtc 2 failed".
However, it's clear that the graphics hardware can handle 3 outputs, since it
refers to "pipe 0, pipe 1 and pipe 2" in the logs.

Google doesn't show anything very helpful, except to warn that in older
graphics hardware (definitely not this motherboard) there may be more output
connectors than graphics pipelines, and that in the HD4600 there are only 2x
PLL, so 2 of the monitors need to be identically clocked (as they indeed are).

I'm using the xorg-edgers package, built a couple of days ago from git, and
this probleme affects both the latest Ubuntu (Saucy), and Mageia Alpha 4. I'm
using a very recent kernel, 3.11.0.

Thanks for your help - please let me know if there's anything I can do to
assist in debugging/testing.

P.S. I originally filed this here, but I think it is really an Xorg bug, rather
than an Ubuntu-specific one.
https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/1215449

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