[Bug 73834] Launch of Qemu VM (with kvm/vfio/iommu/pci-stub) causes [drm:intel_uncore_check_errors] *ERROR* Unclaimed register before interrupt

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=73834

--- Comment #7 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
VGA arbitration. Shudder. I tried to come up with a way to make it work
somehow, and I apparently failed. I'm not going to try again any time soon.

Here's what Daniel had to say when he reverted a bunch of VGA arbiter changes
from the driver. You can follow the link to my stop_machine hack.

commit ebff5fa9d545574324095d9c6a3cb80c9157abc5
Author: Dave Airlie <airlied at redhat.com>
Date:   Fri Oct 11 15:12:04 2013 +1000

    Revert "i915: Update VGA arbiter support for newer devices"

    This reverts commit 81b5c7bc8de3e6f63419139c2fc91bf81dea8a7d.

    Adding drm/i915 into the vga arbiter chain means that X (in a piece of
    well-meant paranoia) will do a get/put on the vga decoding around
    _every_ accel call down into the ddx. Which results in some nice
    performance disasters [1]. This really breaks userspace, by disabling
    DRI for everyone, and stops OpenGL from working, this isn't limited
    to just the i915 but both the integrated and discrete GPUs on
    multi-gpu systems, in other words this causes untold worlds of pain,

    Ville tried to come up with a Great Hack to fiddle the required VGA
    I/O ops behind everyone's back using stop_machine, but that didn't
    really work out [2]. Given that we're fairly late in the -rc stage for
    such games let's just revert this all.

    One thing we might want to keep is to delay the disabling of the vga
    decoding until the fbdev emulation and the fbcon screen is set up. If
    we kill vga mem decoding beforehand fbcon can end up with a white
    square in the top-left corner it tried to save from the vga memory for
    a seamless transition. And we have bug reports on older platforms
    which seem to match these symptoms.

    But again that's something to play around with in -next.

    References: [1]
http://lists.x.org/archives/xorg-devel/2013-September/037763.html
    References: [2] http://www.spinics.net/lists/intel-gfx/msg34062.html
    Cc: Alex Williamson <alex.williamson at redhat.com>
    Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
    Cc: Chris Wilson <chris at chris-wilson.co.uk>
    Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
    Signed-off-by: Dave Airlie <airlied at redhat.com>

-- 
You are receiving this mail because:
You are the QA Contact for the bug.
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.freedesktop.org/archives/intel-gfx-bugs/attachments/20140204/a4ec1735/attachment-0001.html>