[Intel-gfx] [PATCH] drm/i915: Don't register CRT connector when it's fused off

[Ville Syrjälä]

On Sat, Nov 21, 2015 at 10:44:12AM +0000, Chris Wilson wrote:
> On Fri, Nov 20, 2015 at 10:35:41PM +0200, ville.syrjala at linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > On some machines the CRT connector may be fused off. The weird thing
> > about this setup is that the ADPA register works otherwise normally,
> > except the enable bit is hardwired to 0. No one knows of any fuse
> > register that would tell us if this is the case, so the only thing we
> > can do (apart from a blacklist) is to try and set the enable bit and see
> > if it sticks. If not, we don't register the connector at all. Obviously
> > if the bit is already set when loading the driver we can just assume it
> > works.
> > 
> > I've smoke tested this approach on several machines (GMCH and PCH),
> > some with actual CRT connectors, some with shadow connectors, and
> > obviously the machine (IVB) with the fused off connector. So far
> > I've not seen any ill effects from this probe.
> > 
> > The main benefit is that we can actually run igt on machines with
> > fused off connectors, without totally upsetting the state checker.
> > 
> > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> If we can't enable the VGA port, there's not much we can do with it.
> 
> Acked-by: Chris Wilson <chris at chris-wilson.co.uk>
> 
> I'm just a bit hesistant, in case there are machine out there that
> simply do not report the hw state back (doubtful) or there are people
> who make use of the false VGA as a fake output (like me, or perhaps
> kvm-over-ip). I'll survive, I just use a fake HDMI output if there is no
> VGA.

Based on my experience most machines that lack the physical connector
still have a fully working ADPA register. I have two such machines
myself. There's just this one machine at our office where it's
totally fused off, and running igt on it is no fun unless we get rid
of the connector.

-- 
Ville Syrjälä
Intel OTC