drm/i915/gem: clear userspace buffers for LMEM

All userspace objects must be cleared when allocating the backing store,
before they are potentially visible to userspace.  For now use simple
CPU based clearing to do this for device local-memory objects, note that
in the near future this will instead use the blitter engine.
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin@linux.intel.com>
Cc: Jon Bloomfield <jon.bloomfield@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Kenneth Graunke <kenneth@whitecape.org>
Cc: Jason Ekstrand <jason@jlekstrand.net>
Cc: Dave Airlie <airlied@gmail.com>
Cc: dri-devel@lists.freedesktop.org
Cc: mesa-dev@lists.freedesktop.org
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210429103056.407067-8-matthew.auld@intel.com

drivers/gpu/drm/i915/gem/i915_gem_create.c

@@ -71,6 +71,7 @@ static int
 i915_gem_setup(struct drm_i915_gem_object *obj, u64 size)
 {
 	struct intel_memory_region *mr = obj->mm.placements[0];
+	unsigned int flags;
 	int ret;
 
 	size = round_up(size, object_max_page_size(obj));
@@ -83,7 +84,16 @@ i915_gem_setup(struct drm_i915_gem_object *obj, u64 size)
 	if (i915_gem_object_size_2big(size))
 		return -E2BIG;
 
-	ret = mr->ops->init_object(mr, obj, size, 0);
+	/*
+	 * For now resort to CPU based clearing for device local-memory, in the
+	 * near future this will use the blitter engine for accelerated, GPU
+	 * based clearing.
+	 */
+	flags = 0;
+	if (mr->type == INTEL_MEMORY_LOCAL)
+		flags = I915_BO_ALLOC_CPU_CLEAR;
+
+	ret = mr->ops->init_object(mr, obj, size, flags);
 	if (ret)
 		return ret;