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

[Chris Wilson]

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.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre