Re: [PATCH 03/10] drm/i915: Check VBT for CRT port presence on HSW/BDW

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Dec 01, 2015 at 01:41:49PM +0000, Chris Wilson wrote:
> On Tue, Dec 01, 2015 at 03:08:34PM +0200, ville.syrjala@linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > Unfortunatey there appear to quite a few HSW/BDW machines (eg.
> > NUCs, Brix Pro) in the wild with LPT/WPT-H but non-working FDI.
> > FDI training fails every single time on these machines. Dunno,
> > maybe they just didn't bother wiring it up or something?
> > 
> > Unfortunately all the fuse bits and whatnot are telling us that
> > the CRT connector is present. And so what we get from this is tons
> > of false positives from the CI systems due to VGA connector forcing.
> > 
> > I've not found any way to detect this purely from hardware, so we
> > have to resort to looking at the VBT int_crt_support bit. We used
> > to check this bit on all platforms, but that broke all the old
> > machines, so the check was then restricted to VLV only in
> > commit 84b4e042c470 ("drm/i915: only apply crt_present check on VLV")
> > 
> > Considering HSW and VLV VBT probably got defined around the same time,
> > it should be reasonably safe to assume that the bits is sane for
> > HSW/BDW as well. At least I have one copy of some VBT spec here that
> > says it's meant for both VLV and HSW, and it knows about the bit
> > (lists it being valid from version 155 onwards). Also I have two
> > HSW desktop machines with actual CRT ports and both have
> > int_crt_support==1 in their VBTs.
> > 
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_display.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > index e80387dd6582..29ea4c458ab3 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -14263,7 +14263,7 @@ static bool intel_crt_present(struct drm_device *dev)
> >  	if (HAS_DDI(dev) && I915_READ(DDI_BUF_CTL(PORT_A)) & DDI_A_4_LANES)
> >  		return false;
> >  
> > -	if (IS_VALLEYVIEW(dev) && !dev_priv->vbt.int_crt_support)
> > +	if ((HAS_DDI(dev) || IS_VALLEYVIEW(dev)) && !dev_priv->vbt.int_crt_support)
> 
> Would it not be better to move this knowledge to vbt if it is version
> dependent?
> 
> 	vbt.int_crtc_support = (UNKNOWN, NOT_PRESENT, PRESENT)
> 
> then
> 
> 	if (dev_priv->vbt.int_crt_support == NOT_PRESENT)
> >  		return false;

I'm not sure the UNKNWON value really buys us anything. But I suppose we
could just do this:

        general = find_section(bdb, BDB_GENERAL_FEATURES);
        if (general) {
                dev_priv->vbt.int_tv_support = general->int_tv_support;
-               dev_priv->vbt.int_crt_support = general->int_crt_support;
+               if (HAS_DDI(dev_priv) || IS_VALLEYIEW(dev_priv))
+                       dev_priv->vbt.int_crt_support = general->int_crt_support;

The other option is to make it check the version. But I'm not sure if
that's entirely safe. For extra paranoia I guess we could do both,
just in case there's some early VLV/HSW out there with <155 VBT
version.

-- 
Ville Syrjälä
Intel OTC
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