drm/i915: extract and improve gen8_irq_power_well_post_enable

Move it from hsw_power_well_post_enable() (intel_pm.c) to i915_irq.c
so we can reuse the nice IRQ macros we have there. The main difference
is that now we're going to check if the IIR register is non-zero when
we try to re-enable the interrupts.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 6f19420..e2e9bb8f 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -3478,6 +3478,18 @@
 	ibx_irq_reset(dev);
 }
 
+void gen8_irq_power_well_post_enable(struct drm_i915_private *dev_priv)
+{
+	unsigned long irqflags;
+
+	spin_lock_irqsave(&dev_priv->irq_lock, irqflags);
+	GEN8_IRQ_INIT_NDX(DE_PIPE, PIPE_B, dev_priv->de_irq_mask[PIPE_B],
+			  ~dev_priv->de_irq_mask[PIPE_B]);
+	GEN8_IRQ_INIT_NDX(DE_PIPE, PIPE_C, dev_priv->de_irq_mask[PIPE_C],
+			  ~dev_priv->de_irq_mask[PIPE_C]);
+	spin_unlock_irqrestore(&dev_priv->irq_lock, irqflags);
+}
+
 static void cherryview_irq_preinstall(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;