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authorDaniel Vetter <daniel.vetter@ffwll.ch>2012-06-16 15:30:32 +0200
committerDaniel Vetter <daniel.vetter@ffwll.ch>2012-06-16 15:30:32 +0200
commitaaa377302b2994fcc2c66741b47da33feb489dca (patch)
tree184ed8537cc264d64f93553569c0d03da6a94f9e /drivers/gpu/drm/i915/intel_crt.c
parent8e96d9c4d9843f00ebeb4a9b33596d96602ea101 (diff)
drm/i915/crt: Do not rely upon the HPD presence pin
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: commit 9e612a008fa7fe493a473454def56aa321479495 Author: 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: commit 8f53369b753f5f4c7684c2eb0b592152abb1dd00 Author: 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>
Diffstat (limited to 'drivers/gpu/drm/i915/intel_crt.c')
-rw-r--r--drivers/gpu/drm/i915/intel_crt.c15
1 files changed, 12 insertions, 3 deletions
diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
index 75a70c46ef1..5978490dac9 100644
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -453,18 +453,27 @@ intel_crt_detect(struct drm_connector *connector, bool force)
struct intel_load_detect_pipe tmp;
if (I915_HAS_HOTPLUG(dev)) {
+ /* We can not rely on the HPD pin always being correctly wired
+ * up, for example many KVM do not pass it through, and so
+ * only trust an assertion that the monitor is connected.
+ */
if (intel_crt_detect_hotplug(connector)) {
DRM_DEBUG_KMS("CRT detected via hotplug\n");
return connector_status_connected;
- } else {
+ } else
DRM_DEBUG_KMS("CRT not detected via hotplug\n");
- return connector_status_disconnected;
- }
}
if (intel_crt_detect_ddc(connector))
return connector_status_connected;
+ /* Load detection is broken on HPD capable machines. Whoever wants a
+ * broken monitor (without edid) to work behind a broken kvm (that fails
+ * to have the right resistors for HP detection) needs to fix this up.
+ * For now just bail out. */
+ if (I915_HAS_HOTPLUG(dev))
+ return connector_status_disconnected;
+
if (!force)
return connector->status;