From aaa377302b2994fcc2c66741b47da33feb489dca Mon Sep 17 00:00:00 2001 From: Daniel Vetter Date: Sat, 16 Jun 2012 15:30:32 +0200 Subject: [PATCH] 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 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 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 Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=50501 Reviewed-by: Chris Wilson Signed-Off-by: Daniel Vetter --- drivers/gpu/drm/i915/intel_crt.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c index 75a70c46ef1b..5978490dac92 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; -- 2.20.1