1 files changed, 9 insertions, 5 deletions

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index af5c335a69db..efe3fc671e1e 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -142,14 +142,18 @@ static void snb_update_pm_irq(struct drm_i915_private *dev_priv,
                               uint32_t interrupt_mask,
                               uint32_t enabled_irq_mask)
 {
-        uint32_t pmimr = I915_READ(GEN6_PMIMR);
-        pmimr &= ~interrupt_mask;
-        pmimr |= (~enabled_irq_mask & interrupt_mask);
+        uint32_t pmimr, new_val;
 
         assert_spin_locked(&dev_priv->irq_lock);
 
-        I915_WRITE(GEN6_PMIMR, pmimr);
-        POSTING_READ(GEN6_PMIMR);
+        pmimr = new_val = I915_READ(GEN6_PMIMR);
+        new_val &= ~interrupt_mask;
+        new_val |= (~enabled_irq_mask & interrupt_mask);
+
+        if (new_val != pmimr) {
+                I915_WRITE(GEN6_PMIMR, new_val);
+                POSTING_READ(GEN6_PMIMR);
+        }
 }
 
 void snb_enable_pm_irq(struct drm_i915_private *dev_priv, uint32_t mask)