drm/i915: cache the EDID for eDP panels

They aren't going anywhere, and probing on DDC can cause the panel to
blank briefly, so read them up front and cache them for later queries.

v2: fix potential NULL derefs in intel_dp_get_edid_modes and
    intel_dp_get_edid (Jani)
    copy full EDID length, including extension blocks (Takashi)
    free EDID on teardown (Takashi)
v3: malloc a new EDID buffer that's big enough for the memcpy (Chris)
v4: change handling of NULL EDIDs, just preserve the NULL behavior
    across detects and mode list fetches rather than trying to re-fetch
    the EDID (Chris)
v5: be glad that Chris is around to remind me to hit C-x C-s before
    committing.

References: https://bugs.freedesktop.org/show_bug.cgi?id=46856
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_dp.c

@@ -32,6 +32,7 @@
 #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"
@@ -67,6 +68,8 @@ struct intel_dp {
 	struct drm_display_mode *panel_fixed_mode;  /* for eDP */
 	struct delayed_work panel_vdd_work;
 	bool want_panel_vdd;
+	struct edid *edid; /* cached EDID for eDP */
+	int edid_mode_count;
 };
 
 /**
@@ -2125,10 +2128,22 @@ intel_dp_get_edid(struct drm_connector *connector, struct i2c_adapter *adapter)
 {
 	struct intel_dp *intel_dp = intel_attached_dp(connector);
 	struct edid	*edid;
+	int size;
+
+	if (is_edp(intel_dp)) {
+		if (!intel_dp->edid)
+			return NULL;
+
+		size = (intel_dp->edid->extensions + 1) * EDID_LENGTH;
+		edid = kmalloc(size, GFP_KERNEL);
+		if (!edid)
+			return NULL;
+
+		memcpy(edid, intel_dp->edid, size);
+		return edid;
+	}
 
-	ironlake_edp_panel_vdd_on(intel_dp);
 	edid = drm_get_edid(connector, adapter);
-	ironlake_edp_panel_vdd_off(intel_dp, false);
 	return edid;
 }
 
@@ -2138,9 +2153,17 @@ intel_dp_get_edid_modes(struct drm_connector *connector, struct i2c_adapter *ada
 	struct intel_dp *intel_dp = intel_attached_dp(connector);
 	int	ret;
 
-	ironlake_edp_panel_vdd_on(intel_dp);
+	if (is_edp(intel_dp)) {
+		drm_mode_connector_update_edid_property(connector,
+							intel_dp->edid);
+		ret = drm_add_edid_modes(connector, intel_dp->edid);
+		drm_edid_to_eld(connector,
+				intel_dp->edid);
+		connector->display_info.raw_edid = NULL;
+		return intel_dp->edid_mode_count;
+	}
+
 	ret = intel_ddc_get_modes(connector, adapter);
-	ironlake_edp_panel_vdd_off(intel_dp, false);
 	return ret;
 }
 
@@ -2330,6 +2353,7 @@ static void intel_dp_encoder_destroy(struct drm_encoder *encoder)
 	i2c_del_adapter(&intel_dp->adapter);
 	drm_encoder_cleanup(encoder);
 	if (is_edp(intel_dp)) {
+		kfree(intel_dp->edid);
 		cancel_delayed_work_sync(&intel_dp->panel_vdd_work);
 		ironlake_panel_vdd_off_sync(intel_dp);
 	}
@@ -2513,11 +2537,14 @@ intel_dp_init(struct drm_device *dev, int output_reg)
 			break;
 	}
 
+	intel_dp_i2c_init(intel_dp, intel_connector, name);
+
 	/* Cache some DPCD data in the eDP case */
 	if (is_edp(intel_dp)) {
 		bool ret;
 		struct edp_power_seq	cur, vbt;
 		u32 pp_on, pp_off, pp_div;
+		struct edid *edid;
 
 		pp_on = I915_READ(PCH_PP_ON_DELAYS);
 		pp_off = I915_READ(PCH_PP_OFF_DELAYS);
@@ -2585,9 +2612,19 @@ intel_dp_init(struct drm_device *dev, int output_reg)
 			intel_dp_destroy(&intel_connector->base);
 			return;
 		}
-	}
 
-	intel_dp_i2c_init(intel_dp, intel_connector, name);
+		ironlake_edp_panel_vdd_on(intel_dp);
+		edid = drm_get_edid(connector, &intel_dp->adapter);
+		if (edid) {
+			drm_mode_connector_update_edid_property(connector,
+								edid);
+			intel_dp->edid_mode_count =
+				drm_add_edid_modes(connector, edid);
+			drm_edid_to_eld(connector, edid);
+			intel_dp->edid = edid;
+		}
+		ironlake_edp_panel_vdd_off(intel_dp, false);
+	}
 
 	intel_encoder->hot_plug = intel_dp_hot_plug;