[Regression] [PATCH] intel_crt_detect_ddc() seems to be broken for DVI-I

["\"David Müller (ELSOFT AG)\"" <d.mueller@elsoft.ch>]

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Hello

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.

The patch below adds an additional check to make sure that there is
really an analog device attached (similar to the "Mac mini hack" in
intel_sdvo.c)

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Signed-off-by: David Müller <d.mueller@elsoft.ch>

diff -dpurN a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
--- a/drivers/gpu/drm/i915/intel_crt.c	2011-01-05 10:35:18.449000023 +0100
+++ b/drivers/gpu/drm/i915/intel_crt.c	2011-01-06 12:16:47.630998952 +0100
@@ -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 d
 	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
 	}
 
 	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 *c
 		}
 	}
 
-	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 *c
 		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);

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