drm/i915: Determine DP++ type 1 DVI adaptor presence based on VBT

DP dual mode type 1 DVI adaptors aren't required to implement any
registers, so it's a bit hard to detect them. The best way would
be to check the state of the CONFIG1 pin, but we have no way to
do that. So as a last resort, check the VBT to see if the HDMI
port is in fact a dual mode capable DP port.

v2: Deal with VBT code reorganization
    Deal with DRM_DP_DUAL_MODE_UNKNOWN
    Reduce DEVICE_TYPE_DP_DUAL_MODE_BITS a bit
    Accept both DP and HDMI dvo_port in VBT as my BSW
    at least declare its DP port as HDMI :(
v3: Ignore DEVICE_TYPE_NOT_HDMI_OUTPUT (Shashank)

Cc: stable@vger.kernel.org
Cc: Tore Anderson <tore@fud.no>
Reported-by: Tore Anderson <tore@fud.no>
Fixes: 7a0baa623446 ("Revert "drm/i915: Disable 12bpc hdmi for now"")
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Shashank Sharma <shashank.sharma@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1462362322-31278-1-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Shashank Sharma <shashank.sharma@intel.com>
diff --git a/drivers/gpu/drm/i915/intel_bios.c b/drivers/gpu/drm/i915/intel_bios.c
index 8151811..8b68c48 100644
--- a/drivers/gpu/drm/i915/intel_bios.c
+++ b/drivers/gpu/drm/i915/intel_bios.c
@@ -1597,6 +1597,42 @@
 	return false;
 }
 
+bool intel_bios_is_port_dp_dual_mode(struct drm_i915_private *dev_priv, enum port port)
+{
+	static const struct {
+		u16 dp, hdmi;
+	} port_mapping[] = {
+		/*
+		 * Buggy VBTs may declare DP ports as having
+		 * HDMI type dvo_port :( So let's check both.
+		 */
+		[PORT_B] = { DVO_PORT_DPB, DVO_PORT_HDMIB, },
+		[PORT_C] = { DVO_PORT_DPC, DVO_PORT_HDMIC, },
+		[PORT_D] = { DVO_PORT_DPD, DVO_PORT_HDMID, },
+		[PORT_E] = { DVO_PORT_DPE, DVO_PORT_HDMIE, },
+	};
+	int i;
+
+	if (port == PORT_A || port >= ARRAY_SIZE(port_mapping))
+		return false;
+
+	if (!dev_priv->vbt.child_dev_num)
+		return false;
+
+	for (i = 0; i < dev_priv->vbt.child_dev_num; i++) {
+		const union child_device_config *p_child =
+			&dev_priv->vbt.child_dev[i];
+
+		if ((p_child->common.dvo_port == port_mapping[port].dp ||
+		     p_child->common.dvo_port == port_mapping[port].hdmi) &&
+		    (p_child->common.device_type & DEVICE_TYPE_DP_DUAL_MODE_BITS) ==
+		    (DEVICE_TYPE_DP_DUAL_MODE & DEVICE_TYPE_DP_DUAL_MODE_BITS))
+			return true;
+	}
+
+	return false;
+}
+
 /**
  * intel_bios_is_dsi_present - is DSI present in VBT
  * @dev_priv:	i915 device instance