1 files changed, 39 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/intel_runtime_pm.c b/drivers/gpu/drm/i915/intel_runtime_pm.c
index 19e6ff64ce9d..678ed3475d7e 100644
--- a/drivers/gpu/drm/i915/intel_runtime_pm.c
+++ b/drivers/gpu/drm/i915/intel_runtime_pm.c
@@ -470,6 +470,43 @@ static void gen9_set_dc_state_debugmask_memory_up(
         }
 }
 
+static void gen9_write_dc_state(struct drm_i915_private *dev_priv,
+                                u32 state)
+{
+        int rewrites = 0;
+        int rereads = 0;
+        u32 v;
+
+        I915_WRITE(DC_STATE_EN, state);
+
+        /* It has been observed that disabling the dc6 state sometimes
+         * doesn't stick and dmc keeps returning old value. Make sure
+         * the write really sticks enough times and also force rewrite until
+         * we are confident that state is exactly what we want.
+         */
+        do  {
+                v = I915_READ(DC_STATE_EN);
+
+                if (v != state) {
+                        I915_WRITE(DC_STATE_EN, state);
+                        rewrites++;
+                        rereads = 0;
+                } else if (rereads++ > 5) {
+                        break;
+                }
+
+        } while (rewrites < 100);
+
+        if (v != state)
+                DRM_ERROR("Writing dc state to 0x%x failed, now 0x%x\n",
+                          state, v);
+
+        /* Most of the times we need one retry, avoid spam */
+        if (rewrites > 1)
+                DRM_DEBUG_KMS("Rewrote dc state to 0x%x %d times\n",
+                              state, rewrites);
+}
+
 static void gen9_set_dc_state(struct drm_i915_private *dev_priv, uint32_t state)
 {
         uint32_t val;
@@ -502,8 +539,8 @@ static void gen9_set_dc_state(struct drm_i915_private *dev_priv, uint32_t state)
 
         val &= ~mask;
         val |= state;
-        I915_WRITE(DC_STATE_EN, val);
-        POSTING_READ(DC_STATE_EN);
+
+        gen9_write_dc_state(dev_priv, val);
 
         dev_priv->csr.dc_state = val & mask;
 }