DRM/i915: Remove magic to prevent blank screen on gen4 chipsets

Since the root cause is understood now and with the fix

   commit 564ed191
   Author: Imre Deak <imre.deak@intel.com>
   Date:   Fri Jun 13 14:54:21 2014 +0300

       drm/i915: gmch: fix stuck primary plane due to memory self-refresh mode

in place the magic for G4x chipsets introduced with commit

   commit 61bc95c1
   Author: Egbert Eich <eich@suse.com>
   Date:   Mon Mar 4 09:24:38 2013 -0500

       DRM/i915: On G45 enable cursor plane briefly after enabling the display plane.

to avoided occasional screen blanking on mode changes can finally
be removed.
It's been verified that Imre's fix also resolves the said issue.
Signed-off-by: Egbert Eich <eich@suse.de>
Tested-by: Stefan Dirsch <sndirsch@suse.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -3894,30 +3894,6 @@ static void intel_crtc_dpms_overlay(struct intel_crtc *intel_crtc, bool enable)
 	 */
 }
 
-/**
- * i9xx_fixup_plane - ugly workaround for G45 to fire up the hardware
- * cursor plane briefly if not already running after enabling the display
- * plane.
- * This workaround avoids occasional blank screens when self refresh is
- * enabled.
- */
-static void
-g4x_fixup_plane(struct drm_i915_private *dev_priv, enum pipe pipe)
-{
-	u32 cntl = I915_READ(CURCNTR(pipe));
-
-	if ((cntl & CURSOR_MODE) == 0) {
-		u32 fw_bcl_self = I915_READ(FW_BLC_SELF);
-
-		I915_WRITE(FW_BLC_SELF, fw_bcl_self & ~FW_BLC_SELF_EN);
-		I915_WRITE(CURCNTR(pipe), CURSOR_MODE_64_ARGB_AX);
-		intel_wait_for_vblank(dev_priv->dev, pipe);
-		I915_WRITE(CURCNTR(pipe), cntl);
-		I915_WRITE(CURBASE(pipe), I915_READ(CURBASE(pipe)));
-		I915_WRITE(FW_BLC_SELF, fw_bcl_self);
-	}
-}
-
 static void intel_crtc_enable_planes(struct drm_crtc *crtc)
 {
 	struct drm_device *dev = crtc->dev;
@@ -3930,9 +3906,6 @@ static void intel_crtc_enable_planes(struct drm_crtc *crtc)
 
 	intel_enable_primary_hw_plane(dev_priv, plane, pipe);
 	intel_enable_planes(crtc);
-	/* The fixup needs to happen before cursor is enabled */
-	if (IS_G4X(dev))
-		g4x_fixup_plane(dev_priv, pipe);
 	intel_crtc_update_cursor(crtc, true);
 	intel_crtc_dpms_overlay(intel_crtc, true);