drm/i915/bdw: PIPE_[BC] I[ME]R moved to powerwell

The pipe B and pipe C interrupt mask and enable registers are now part
of the pipe, so disabling the pipe power wells will lost the contests of
the registers.

Art totally debugged this one!

v2: Use the irq_lock to clarify code, and prevent future bugs (Daniel)

Cc: Art Runyan <arthur.j.runyan@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
[danvet: Make sparse happy.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -5684,6 +5684,7 @@ static void __intel_set_power_well(struct drm_device *dev, bool enable)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	bool is_enabled, enable_requested;
+	unsigned long irqflags;
 	uint32_t tmp;
 
 	tmp = I915_READ(HSW_PWR_WELL_DRIVER);
@@ -5701,9 +5702,24 @@ static void __intel_set_power_well(struct drm_device *dev, bool enable)
 				      HSW_PWR_WELL_STATE_ENABLED), 20))
 				DRM_ERROR("Timeout enabling power well\n");
 		}
+
+		if (IS_BROADWELL(dev)) {
+			spin_lock_irqsave(&dev_priv->irq_lock, irqflags);
+			I915_WRITE(GEN8_DE_PIPE_IMR(PIPE_B),
+				   dev_priv->de_irq_mask[PIPE_B]);
+			I915_WRITE(GEN8_DE_PIPE_IER(PIPE_B),
+				   ~dev_priv->de_irq_mask[PIPE_B] |
+				   GEN8_PIPE_VBLANK);
+			I915_WRITE(GEN8_DE_PIPE_IMR(PIPE_C),
+				   dev_priv->de_irq_mask[PIPE_C]);
+			I915_WRITE(GEN8_DE_PIPE_IER(PIPE_C),
+				   ~dev_priv->de_irq_mask[PIPE_C] |
+				   GEN8_PIPE_VBLANK);
+			POSTING_READ(GEN8_DE_PIPE_IER(PIPE_C));
+			spin_unlock_irqrestore(&dev_priv->irq_lock, irqflags);
+		}
 	} else {
 		if (enable_requested) {
-			unsigned long irqflags;
 			enum pipe p;
 
 			I915_WRITE(HSW_PWR_WELL_DRIVER, 0);