drm/i915/icl: Prevent incorrect DBuf enabling

Pretend that we have only 1 DBuf slice and that 1 slice is always
enabled, until we have a proper way for on-demand toggling of the second
slice.  Currently we'll try to incorrectly enable DBuf even when all
pipes are disabled and we are already runtime suspended (as the computed
number of DBuf slices will be 1 in that case).

This also means we'll leave the second slice enabled redundantly (except
when suspended), but that's an acceptable tradeoff until we have a
proper solution.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108756
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190307103235.23538-1-imre.deak@intel.com

drivers/gpu/drm/i915/intel_pm.c

@@ -3624,7 +3624,12 @@ static u8 intel_enabled_dbuf_slices_num(struct drm_i915_private *dev_priv)
 	if (INTEL_GEN(dev_priv) < 11)
 		return enabled_slices;
 
-	if (I915_READ(DBUF_CTL_S2) & DBUF_POWER_STATE)
+	/*
+	 * FIXME: for now we'll only ever use 1 slice; pretend that we have
+	 * only that 1 slice enabled until we have a proper way for on-demand
+	 * toggling of the second slice.
+	 */
+	if (0 && I915_READ(DBUF_CTL_S2) & DBUF_POWER_STATE)
 		enabled_slices++;
 
 	return enabled_slices;

drivers/gpu/drm/i915/intel_runtime_pm.c

@@ -3576,7 +3576,11 @@ static void icl_dbuf_enable(struct drm_i915_private *dev_priv)
 	    !(I915_READ(DBUF_CTL_S2) & DBUF_POWER_STATE))
 		DRM_ERROR("DBuf power enable timeout\n");
 	else
-		dev_priv->wm.skl_hw.ddb.enabled_slices = 2;
+		/*
+		 * FIXME: for now pretend that we only have 1 slice, see
+		 * intel_enabled_dbuf_slices_num().
+		 */
+		dev_priv->wm.skl_hw.ddb.enabled_slices = 1;
 }
 
 static void icl_dbuf_disable(struct drm_i915_private *dev_priv)
@@ -3591,7 +3595,11 @@ static void icl_dbuf_disable(struct drm_i915_private *dev_priv)
 	    (I915_READ(DBUF_CTL_S2) & DBUF_POWER_STATE))
 		DRM_ERROR("DBuf power disable timeout!\n");
 	else
-		dev_priv->wm.skl_hw.ddb.enabled_slices = 0;
+		/*
+		 * FIXME: for now pretend that the first slice is always
+		 * enabled, see intel_enabled_dbuf_slices_num().
+		 */
+		dev_priv->wm.skl_hw.ddb.enabled_slices = 1;
 }
 
 static void icl_mbus_init(struct drm_i915_private *dev_priv)