aaa377302b
VGA hotplug detection "works" by measuring the resistance across certain pins. A lot of kvm switches fumble this and wire up cheap resistors with the wrong resistance or don't bother at all. To accomodate these, also try to detect a connected monitor by trying to grab the edid. Contrary to !HAS_HOTPLUG platforms we don't bother with an actual load-detection cycle when the output is life - that would be actual work to implement because things moved around. This is the big difference to Chris Wilson's original approach: commit9e612a008fAuthor: Chris Wilson <chris@chris-wilson.co.uk> Date: Thu May 31 13:08:53 2012 +0100 drm/i915/crt: Do not rely upon the HPD presence pin This blew up on Linus' machine because it errornously detected a vga screen (without and edid and hence only the default modes), leading to it's prompt removal: commit8f53369b75Author: Linus Torvalds <torvalds@linux-foundation.org> Date: Fri Jun 8 14:53:06 2012 -0700 Revert "drm/i915/crt: Do not rely upon the HPD presence pin" Some digging around in Bspec shows the reason why load detect doesn't work on newer chips - the legacy VGA load detect bit isn't wired up any longer: Public Snb Bspec, Vol3 Part1, 1.1.1 ST00 Input Status 0, bit4: "RGB Comparator / Sense. This bit is here for compatibility and will always return one. Monitor detection must be done be done through the programming of registers in the MMIO space. 0 = Below threshold 1 = Above threshold" v2: Add a comment in the code that load detect on hotplug capable machines is broken and pimp the commit message with a quote of Bspec to show why. Reported-and-tested-by: Matthieu LAVIE <boiteamadmax@hotmail.com> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=50501 Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
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* For the very latest on DRI development, please see: *
* http://dri.freedesktop.org/ *
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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