drm/i915: Return a default RCS context size

Instead of returning whatever size the latest GEN used. This is because
context sizes for new GENs can go up or down, but the only safe thing to
do for missing cases is to use the largest known one, whatever that is.
Suggested-by: NRodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: NDaniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: NOscar Mateo <oscar.mateo@intel.com>
Signed-off-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1515711307-28979-1-git-send-email-oscar.mateo@intel.com

drivers/gpu/drm/i915/intel_engine_cs.c

@@ -38,6 +38,7 @@
  */
 #define HSW_CXT_TOTAL_SIZE		(17 * PAGE_SIZE)
 
+#define DEFAULT_LR_CONTEXT_RENDER_SIZE	(22 * PAGE_SIZE)
 #define GEN8_LR_CONTEXT_RENDER_SIZE	(20 * PAGE_SIZE)
 #define GEN9_LR_CONTEXT_RENDER_SIZE	(22 * PAGE_SIZE)
 #define GEN10_LR_CONTEXT_RENDER_SIZE	(18 * PAGE_SIZE)
@@ -157,6 +158,7 @@ __intel_engine_context_size(struct drm_i915_private *dev_priv, u8 class)
 		switch (INTEL_GEN(dev_priv)) {
 		default:
 			MISSING_CASE(INTEL_GEN(dev_priv));
+			return DEFAULT_LR_CONTEXT_RENDER_SIZE;
 		case 10:
 			return GEN10_LR_CONTEXT_RENDER_SIZE;
 		case 9: