drm/i915/skl: Don't allow disabling ppgtt and execlists on gen9+

Running the driver without execlists and hence PPGTT (either aliasing or
full) isn't a supported configuration on gen9+.
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -43,7 +43,12 @@ static int sanitize_enable_ppgtt(struct drm_device *dev, int enable_ppgtt)
 	if (IS_GEN8(dev))
 		has_full_ppgtt = false; /* XXX why? */
 
-	if (enable_ppgtt == 0 || !has_aliasing_ppgtt)
+	/*
+	 * We don't allow disabling PPGTT for gen9+ as it's a requirement for
+	 * execlists, the sole mechanism available to submit work.
+	 */
+	if (INTEL_INFO(dev)->gen < 9 &&
+	    (enable_ppgtt == 0 || !has_aliasing_ppgtt))
 		return 0;
 
 	if (enable_ppgtt == 1)

drivers/gpu/drm/i915/intel_lrc.c

@@ -220,6 +220,9 @@ int intel_sanitize_enable_execlists(struct drm_device *dev, int enable_execlists
 {
 	WARN_ON(i915.enable_ppgtt == -1);
 
+	if (INTEL_INFO(dev)->gen >= 9)
+		return 1;
+
 	if (enable_execlists == 0)
 		return 0;