drm/i915: Make sure pipe interrupts are processed before turning off power well on BDW+

Starting from BDW the DE_PIPE interrupts for pipe B and C belong to the
relevant display power well. So we should make sure we've finished
processing them before turning off the power well.

The pipe interrupts shouldn't really happen at this point anymore since
we've already shut down the planes/pipes/whatnot, but being a bit
paranoid shouldn't hurt.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1455907651-16397-1-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index c208ca6..4852049 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -993,6 +993,8 @@
 int intel_get_crtc_scanline(struct intel_crtc *crtc);
 void gen8_irq_power_well_post_enable(struct drm_i915_private *dev_priv,
 				     unsigned int pipe_mask);
+void gen8_irq_power_well_pre_disable(struct drm_i915_private *dev_priv,
+				     unsigned int pipe_mask);
 
 /* intel_crt.c */
 void intel_crt_init(struct drm_device *dev);