drm/i915: POSTING_READ() in intel_set_memory_cxsr()

We want cxsr exit to happen ASAP, so toss in some POSTING_READ()s to
make sure things are really kicked off.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Clint Taylor <Clinton.A.Taylor@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -334,22 +334,27 @@ void intel_set_memory_cxsr(struct drm_i915_private *dev_priv, bool enable)
 
 	if (IS_VALLEYVIEW(dev)) {
 		I915_WRITE(FW_BLC_SELF_VLV, enable ? FW_CSPWRDWNEN : 0);
+		POSTING_READ(FW_BLC_SELF_VLV);
 		if (IS_CHERRYVIEW(dev))
 			chv_set_memory_pm5(dev_priv, enable);
 	} else if (IS_G4X(dev) || IS_CRESTLINE(dev)) {
 		I915_WRITE(FW_BLC_SELF, enable ? FW_BLC_SELF_EN : 0);
+		POSTING_READ(FW_BLC_SELF);
 	} else if (IS_PINEVIEW(dev)) {
 		val = I915_READ(DSPFW3) & ~PINEVIEW_SELF_REFRESH_EN;
 		val |= enable ? PINEVIEW_SELF_REFRESH_EN : 0;
 		I915_WRITE(DSPFW3, val);
+		POSTING_READ(DSPFW3);
 	} else if (IS_I945G(dev) || IS_I945GM(dev)) {
 		val = enable ? _MASKED_BIT_ENABLE(FW_BLC_SELF_EN) :
 			       _MASKED_BIT_DISABLE(FW_BLC_SELF_EN);
 		I915_WRITE(FW_BLC_SELF, val);
+		POSTING_READ(FW_BLC_SELF);
 	} else if (IS_I915GM(dev)) {
 		val = enable ? _MASKED_BIT_ENABLE(INSTPM_SELF_EN) :
 			       _MASKED_BIT_DISABLE(INSTPM_SELF_EN);
 		I915_WRITE(INSTPM, val);
+		POSTING_READ(INSTPM);
 	} else {
 		return;
 	}