On Mon, 11 Jun 2012 16:38:40 +0200, Daniel Vetter <daniel.vetter at ffwll.ch> wrote: > 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 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 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" > > 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 at hotmail.com> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=50501 > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk> Just missing your s-o-b, and you can add my reviewed-by to your amendment. :) -Chris -- Chris Wilson, Intel Open Source Technology Centre
