drm/i915/vlv: disable PPGTT on early revs v3

Early revs didn't have PPGTT support, so disable there.

v2: add debug msg when disabling on early stepping
v3: enable on other B3 packages as well (untested) (Ville)

References: https://bugs.freedesktop.org/show_bug.cgi?id=79669
References: https://bugs.freedesktop.org/show_bug.cgi?id=79670
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Acked-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -63,6 +63,12 @@ static int sanitize_enable_ppgtt(struct drm_device *dev, int enable_ppgtt)
 	}
 #endif
 
+	/* Early VLV doesn't have this */
+	if (IS_VALLEYVIEW(dev) && dev->pdev->revision < 0xb) {
+		DRM_DEBUG_DRIVER("disabling PPGTT on pre-B3 step VLV\n");
+		return 0;
+	}
+
 	return HAS_ALIASING_PPGTT(dev) ? 1 : 0;
 }