drm/i915: only enable HWSTAM interrupts on postinstall on ILK+

We should only enable interrupts at postinstall.

And now on ILK/SNB/IVB/HSW the irq_preinstall and irq_postinstall
functions leave the hardware in the same state.
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
[danvet: Fix compile fail due to drm_i915_private_t typedef removal.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_irq.c

@@ -2912,6 +2912,8 @@ static void ironlake_irq_reset(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
+	I915_WRITE(HWSTAM, 0xffffffff);
+
 	GEN5_IRQ_RESET(DE);
 	if (IS_GEN7(dev))
 		I915_WRITE(GEN7_ERR_INT, 0xffffffff);
@@ -2923,10 +2925,6 @@ static void ironlake_irq_reset(struct drm_device *dev)
 
 static void ironlake_irq_preinstall(struct drm_device *dev)
 {
-	struct drm_i915_private *dev_priv = dev->dev_private;
-
-	I915_WRITE(HWSTAM, 0xeffe);
-
 	ironlake_irq_reset(dev);
 }
 
@@ -3099,6 +3097,8 @@ static int ironlake_irq_postinstall(struct drm_device *dev)
 
 	dev_priv->irq_mask = ~display_mask;
 
+	I915_WRITE(HWSTAM, 0xeffe);
+
 	ibx_irq_pre_postinstall(dev);
 
 	GEN5_IRQ_INIT(DE, dev_priv->irq_mask, display_mask | extra_mask);
@@ -3354,8 +3354,6 @@ static void ironlake_irq_uninstall(struct drm_device *dev)
 
 	intel_hpd_irq_uninstall(dev_priv);
 
-	I915_WRITE(HWSTAM, 0xffffffff);
-
 	ironlake_irq_reset(dev);
 }