From: Chris Wilson <chris at chris-wilson.co.uk>
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 value 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 at 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 at linux-foundation.org>
Date: Fri Jun 8 14:53:06 2012 -0700
Revert "drm/i915/crt: Do not rely upon the HPD presence pin"
Reported-and-tested-by: Matthieu LAVIE <boiteamadmax at hotmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=50501
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
drivers/gpu/drm/i915/intel_crt.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
index 75a70c4..7155181 100644
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -453,18 +453,23 @@ 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;
+ if (I915_HAS_HOTPLUG(dev))
+ return connector_status_disconnected;
+
if (!force)
return connector->status;
--
1.7.10
