drm/i915/crt: Check for a analog monitor in case of DVI-I

Since Linux 2.6.36 the digital output on my system (855GME + DVI-I) is
not working any longer. The analog output is always activated
regardless of the type of monitor attached.

The culprit seems to be intel_crt_detect_ddc(), which returns true as
soon as an ACK from the EDID device is received. Obviously this
approach does not work with DVI-I where the analog and digital outputs
share a common DDC bus.

In a similar manner to the shared DDC wire, ala the "Mac Mini Hack", we
need an additional check to make sure that there really is an analog
device attached to the DDC.
Signed-off-by: David Müller <d.mueller@elsoft.ch>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@kernel.org

drivers/gpu/drm/i915/intel_crt.c

@@ -30,6 +30,7 @@
 #include "drm.h"
 #include "drm_crtc.h"
 #include "drm_crtc_helper.h"
+#include "drm_edid.h"
 #include "intel_drv.h"
 #include "i915_drm.h"
 #include "i915_drv.h"
@@ -287,8 +288,9 @@ static bool intel_crt_ddc_probe(struct drm_i915_private *dev_priv, int ddc_bus)
 	return i2c_transfer(&dev_priv->gmbus[ddc_bus].adapter, msgs, 1) == 1;
 }
 
-static bool intel_crt_detect_ddc(struct intel_crt *crt)
+static bool intel_crt_detect_ddc(struct drm_connector *connector)
 {
+	struct intel_crt *crt = intel_attached_crt(connector);
 	struct drm_i915_private *dev_priv = crt->base.base.dev->dev_private;
 
 	/* CRT should always be at 0, but check anyway */
@@ -301,8 +303,26 @@ static bool intel_crt_detect_ddc(struct intel_crt *crt)
 	}
 
 	if (intel_ddc_probe(&crt->base, dev_priv->crt_ddc_pin)) {
-		DRM_DEBUG_KMS("CRT detected via DDC:0x50 [EDID]\n");
-		return true;
+		struct edid *edid;
+		bool is_digital = false;
+
+		edid = drm_get_edid(connector,
+			&dev_priv->gmbus[dev_priv->crt_ddc_pin].adapter);
+		/*
+		 * This may be a DVI-I connector with a shared DDC
+		 * link between analog and digital outputs, so we
+		 * have to check the EDID input spec of the attached device.
+		 */
+		if (edid != NULL) {
+			is_digital = edid->input & DRM_EDID_INPUT_DIGITAL;
+			connector->display_info.raw_edid = NULL;
+			kfree(edid);
+		}
+
+		if (!is_digital) {
+			DRM_DEBUG_KMS("CRT detected via DDC:0x50 [EDID]\n");
+			return true;
+		}
 	}
 
 	return false;
@@ -458,7 +478,7 @@ intel_crt_detect(struct drm_connector *connector, bool force)
 		}
 	}
 
-	if (intel_crt_detect_ddc(crt))
+	if (intel_crt_detect_ddc(connector))
 		return connector_status_connected;
 
 	if (!force)
@@ -472,7 +492,7 @@ intel_crt_detect(struct drm_connector *connector, bool force)
 		crtc = intel_get_load_detect_pipe(&crt->base, connector,
 						  NULL, &dpms_mode);
 		if (crtc) {
-			if (intel_crt_detect_ddc(crt))
+			if (intel_crt_detect_ddc(connector))
 				status = connector_status_connected;
 			else
 				status = intel_crt_load_detect(crtc, crt);