drm/i915: IVB FBC WaFbcDisableDpfcClockGating

Display register 42020h bit 9 must be set to 1b for the entire time that
Frame Buffer Compression is enabled.

v2: RMW to preserve other bits (by Ville)
v3: Fix from Ville: sed &/| at RMW
v4: Too far on sed.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NRodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -242,6 +242,12 @@ static void ironlake_disable_fbc(struct drm_device *dev)
 		dpfc_ctl &= ~DPFC_CTL_EN;
 		I915_WRITE(ILK_DPFC_CONTROL, dpfc_ctl);
 
+		if (IS_IVYBRIDGE(dev))
+			/* WaFbcDisableDpfcClockGating */
+			I915_WRITE(ILK_DSPCLK_GATE_D,
+				   I915_READ(ILK_DSPCLK_GATE_D) &
+				   ~ILK_DPFCUNIT_CLOCK_GATE_DISABLE);
+
 		DRM_DEBUG_KMS("disabled FBC\n");
 	}
 }
@@ -270,6 +276,11 @@ static void gen7_enable_fbc(struct drm_crtc *crtc, unsigned long interval)
 
 	/* WaFbcAsynchFlipDisableFbcQueue */
 	I915_WRITE(ILK_DISPLAY_CHICKEN1, ILK_FBCQ_DIS);
+	/* WaFbcDisableDpfcClockGating */
+	I915_WRITE(ILK_DSPCLK_GATE_D,
+		   I915_READ(ILK_DSPCLK_GATE_D) |
+		   ILK_DPFCUNIT_CLOCK_GATE_DISABLE);
+
 	I915_WRITE(SNB_DPFC_CTL_SA,
 		   SNB_CPU_FENCE_ENABLE | obj->fence_reg);
 	I915_WRITE(DPFC_CPU_FENCE_OFFSET, crtc->y);