drm/i915/gen9: Extend dmc debug mask to include cores

Cores need to be included into the debug mask. We don't exactly
know what it does but the spec says it must be enabled. So obey.

v2: Cores should be only set for BXT (Imre, Art)

Cc: Imre Deak <imre.deak@intel.com>
Cc: Runyan, Arthur J <arthur.j.runyan@intel.com>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1455877564-5128-1-git-send-email-mika.kuoppala@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -7568,6 +7568,7 @@ enum skl_disp_power_wells {
 #define  DC_STATE_EN_UPTO_DC5_DC6_MASK   0x3
 
 #define  DC_STATE_DEBUG                  _MMIO(0x45520)
+#define  DC_STATE_DEBUG_MASK_CORES	(1<<0)
 #define  DC_STATE_DEBUG_MASK_MEMORY_UP	(1<<1)
 
 /* Please see hsw_read_dcomp() and hsw_write_dcomp() before using this register,

drivers/gpu/drm/i915/intel_runtime_pm.c

@@ -456,15 +456,19 @@ static void assert_can_disable_dc9(struct drm_i915_private *dev_priv)
 	  */
 }
 
-static void gen9_set_dc_state_debugmask_memory_up(
-			struct drm_i915_private *dev_priv)
+static void gen9_set_dc_state_debugmask(struct drm_i915_private *dev_priv)
 {
-	uint32_t val;
+	uint32_t val, mask;
+
+	mask = DC_STATE_DEBUG_MASK_MEMORY_UP;
+
+	if (IS_BROXTON(dev_priv))
+		mask |= DC_STATE_DEBUG_MASK_CORES;
 
 	/* The below bit doesn't need to be cleared ever afterwards */
 	val = I915_READ(DC_STATE_DEBUG);
-	if (!(val & DC_STATE_DEBUG_MASK_MEMORY_UP)) {
-		val |= DC_STATE_DEBUG_MASK_MEMORY_UP;
+	if ((val & mask) != mask) {
+		val |= mask;
 		I915_WRITE(DC_STATE_DEBUG, val);
 		POSTING_READ(DC_STATE_DEBUG);
 	}
@@ -526,7 +530,7 @@ static void gen9_set_dc_state(struct drm_i915_private *dev_priv, uint32_t state)
 		state = DC_STATE_EN_UPTO_DC5;
 
 	if (state & DC_STATE_EN_UPTO_DC5_DC6_MASK)
-		gen9_set_dc_state_debugmask_memory_up(dev_priv);
+		gen9_set_dc_state_debugmask(dev_priv);
 
 	val = I915_READ(DC_STATE_EN);
 	DRM_DEBUG_KMS("Setting DC state from %02x to %02x\n",