drm/plane-helper: Skip prepare_fb/cleanup_fb when newfb==oldfb

When commiting a plane update where the framebuffer doesn't change, we
can skip the prepare_fb/cleanup_fb steps.  This also allows us to avoid
an unnecessary vblank wait at the end of the operation when we're just
moving a plane and not changing its image (e.g., for a cursor).

At the moment, i915 is the only upstream driver using the transitional
plane helpers, and thus the only driver affected by this change.

Note that this replicates a corresponding change in the atomic helpers
implemented in

commit ab58e3384b9f9863bfd029b458ff337d381bf6d2
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Mon Nov 24 20:42:42 2014 +0100

    drm/atomic-helper: Skip vblank waits for unchanged fbs

Reported-by: Jeremiah Mahler <jmmahler@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=88540
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Tested-by: Tested-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/drm_plane_helper.c b/drivers/gpu/drm/drm_plane_helper.c
index f24c4cfe674b9e0d75a36f0ab017afef7bcddb5f..7a5814afe31abd695a6fc291902a4743cec5c90e 100644 (file)
--- a/drivers/gpu/drm/drm_plane_helper.c
+++ b/drivers/gpu/drm/drm_plane_helper.c
@@ -435,7 +435,8 @@ int drm_plane_helper_commit(struct drm_plane *plane,
                        goto out;
        }
 
-       if (plane_funcs->prepare_fb && plane_state->fb) {
+       if (plane_funcs->prepare_fb && plane_state->fb &&
+           plane_state->fb != old_fb) {
                ret = plane_funcs->prepare_fb(plane, plane_state->fb);
                if (ret)
                        goto out;
@@ -456,6 +457,13 @@ int drm_plane_helper_commit(struct drm_plane *plane,
                        crtc_funcs[i]->atomic_flush(crtc[i]);
        }
 
+       /*
+        * If we only moved the plane and didn't change fb's, there's no need to
+        * wait for vblank.
+        */
+       if (plane->state->fb == old_fb)
+               goto out;
+
        for (i = 0; i < 2; i++) {
                if (!crtc[i])
                        continue;