drm/i915: Check VBT for CRT port presence on HSW/BDW

Unfortunatey there appear to quite a few HSW/BDW machines (eg.
NUCs, Brix Pro) in the wild with LPT/WPT-H that have no physical
CRT connector and 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 84b4e042 ("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
desktop machines with actual CRT ports and both have
int_crt_support==1 in their VBTs.

Also we already trust VBT >= 155 to tell us various details about
the DDI ports, so trusting it a bit more seems reasonable.

As far as VLV goes, the added VBT version check should be fine. Even
if someone has some weird VLV machine with a very old VBT version,
it just means they'll end up with a shadow CRT connector. IIRC the
reason for eliminating the shadow CRT connector on VLV was to speed
up display probing rather than fixing something more serious.

v2: Move the platform checks into the VBT parsing code
    Also check that the VBT version is at least 155
v3: Improve commit message (Paulo)

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1449005493-15487-1-git-send-email-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/intel_bios.c

@@ -356,7 +356,10 @@ parse_general_features(struct drm_i915_private *dev_priv,
 	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;
+		/* int_crt_support can't be trusted on earlier platforms */
+		if (bdb->version >= 155 &&
+		    (HAS_DDI(dev_priv) || IS_VALLEYVIEW(dev_priv)))
+			dev_priv->vbt.int_crt_support = general->int_crt_support;
 		dev_priv->vbt.lvds_use_ssc = general->enable_ssc;
 		dev_priv->vbt.lvds_ssc_freq =
 			intel_bios_ssc_frequency(dev, general->ssc_freq);

drivers/gpu/drm/i915/intel_display.c

@@ -14264,7 +14264,7 @@ 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 (!dev_priv->vbt.int_crt_support)
 		return false;
 
 	return true;