drm/i915: Clear VLV_MASTER_IER around irq processing

Like on CHV, let's clear out the master irq enable bit when we ack
GT/PM interrupts. This will allow GT/PM interrupts to re-raise the
CPU interrupt if we fail to clear all the bits from the IIR(s).

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1460571598-24452-5-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_irq.c

@@ -1781,13 +1781,7 @@ static irqreturn_t valleyview_irq_handler(int irq, void *arg)
 		/* Find, clear, then process each source of interrupt */
 
 		gt_iir = I915_READ(GTIIR);
-		if (gt_iir)
-			I915_WRITE(GTIIR, gt_iir);
-
 		pm_iir = I915_READ(GEN6_PMIIR);
-		if (pm_iir)
-			I915_WRITE(GEN6_PMIIR, pm_iir);
-
 		iir = I915_READ(VLV_IIR);
 
 		if (gt_iir == 0 && pm_iir == 0 && iir == 0)
@@ -1795,6 +1789,13 @@ static irqreturn_t valleyview_irq_handler(int irq, void *arg)
 
 		ret = IRQ_HANDLED;
 
+		I915_WRITE(VLV_MASTER_IER, 0);
+
+		if (gt_iir)
+			I915_WRITE(GTIIR, gt_iir);
+		if (pm_iir)
+			I915_WRITE(GEN6_PMIIR, pm_iir);
+
 		if (gt_iir)
 			snb_gt_irq_handler(dev, dev_priv, gt_iir);
 		if (pm_iir)
@@ -1813,6 +1814,9 @@ static irqreturn_t valleyview_irq_handler(int irq, void *arg)
 		 */
 		if (iir)
 			I915_WRITE(VLV_IIR, iir);
+
+		I915_WRITE(VLV_MASTER_IER, MASTER_INTERRUPT_ENABLE);
+		POSTING_READ(VLV_MASTER_IER);
 	}
 
 out: