[Intel-gfx] [PATCH] drm/i915/userptr: Don't mark readonly objects as dirty

[Chris Wilson]

If we map an object as readonly into the GTT, we know that the GPU
cannot have written to it and so the object is not dirty and we don't
need to flush the writes back to the system.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
index 32d208ede343..b9d2bb15e4a6 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
@@ -663,6 +663,14 @@ i915_gem_userptr_put_pages(struct drm_i915_gem_object *obj,
 	__i915_gem_object_release_shmem(obj, pages, true);
 	i915_gem_gtt_finish_pages(obj, pages);
 
+	/*
+	 * We always mark objects as dirty when they are used by the GPU,
+	 * just in case. However, if we set the vma as being read-only we know
+	 * that the object will never have been written to.
+	 */
+	if (i915_gem_object_is_readonly(obj))
+		obj->mm.dirty = false;
+
 	for_each_sgt_page(page, sgt_iter, pages) {
 		if (obj->mm.dirty)
 			/*
-- 
2.20.1