This reverts commit 81b5c7bc8d.
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@redhat.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>
************************************************************
* For the very latest on DRI development, please see: *
* http://dri.freedesktop.org/ *
************************************************************
The Direct Rendering Manager (drm) is a device-independent kernel-level
device driver that provides support for the XFree86 Direct Rendering
Infrastructure (DRI).
The DRM supports the Direct Rendering Infrastructure (DRI) in four major
ways:
1. The DRM provides synchronized access to the graphics hardware via
the use of an optimized two-tiered lock.
2. The DRM enforces the DRI security policy for access to the graphics
hardware by only allowing authenticated X11 clients access to
restricted regions of memory.
3. The DRM provides a generic DMA engine, complete with multiple
queues and the ability to detect the need for an OpenGL context
switch.
4. The DRM is extensible via the use of small device-specific modules
that rely extensively on the API exported by the DRM module.
Documentation on the DRI is available from:
http://dri.freedesktop.org/wiki/Documentation
http://sourceforge.net/project/showfiles.php?group_id=387
http://dri.sourceforge.net/doc/
For specific information about kernel-level support, see:
The Direct Rendering Manager, Kernel Support for the Direct Rendering
Infrastructure
http://dri.sourceforge.net/doc/drm_low_level.html
Hardware Locking for the Direct Rendering Infrastructure
http://dri.sourceforge.net/doc/hardware_locking_low_level.html
A Security Analysis of the Direct Rendering Infrastructure
http://dri.sourceforge.net/doc/security_low_level.html
ebff5fa9d5