[PATCH] RFC: drm/atomic-helpers: remove legacy_cursor_update hacks

[Daniel Vetter]

The stuff never really worked, and leads to lots of fun because it
out-of-order frees atomic states. Which upsets KASAN, among other
things.

For async updates we now have a more solid solution with the
->atomic_async_check and ->atomic_async_commit hooks. Support for that
for msm and vc4 landed. nouveau and i915 have their own commit
routines, doing something similar.

For everyone else it's probably better to remove the use-after-free
bug, and encourage folks to use the async support instead. The
affected drivers which register a legacy cursor plane and don't either
use the new async stuff or their own commit routine are: amdgpu,
atmel, mediatek, qxl, rockchip, sti, sun4i, tegra, virtio, and vmwgfx.

Inspired by an amdgpu bug report.

References: https://bugzilla.kernel.org/show_bug.cgi?id=199425
Cc: mikita.lipski at amd.com
Cc: Michel Dänzer <michel at daenzer.net>
Cc: harry.wentland at amd.com
Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
---
 drivers/gpu/drm/drm_atomic_helper.c | 13 -------------
 1 file changed, 13 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 130da5195f3b..5a576cdf26dd 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1330,13 +1330,6 @@ drm_atomic_helper_wait_for_vblanks(struct drm_device *dev,
 	int i, ret;
 	unsigned crtc_mask = 0;
 
-	 /*
-	  * Legacy cursor ioctls are completely unsynced, and userspace
-	  * relies on that (by doing tons of cursor updates).
-	  */
-	if (old_state->legacy_cursor_update)
-		return;
-
 	for_each_oldnew_crtc_in_state(old_state, crtc, old_crtc_state, new_crtc_state, i) {
 		if (!new_crtc_state->active)
 			continue;
@@ -1884,12 +1877,6 @@ int drm_atomic_helper_setup_commit(struct drm_atomic_state *state,
 			continue;
 		}
 
-		/* Legacy cursor updates are fully unsynced. */
-		if (state->legacy_cursor_update) {
-			complete_all(&commit->flip_done);
-			continue;
-		}
-
 		if (!new_crtc_state->event) {
 			commit->event = kzalloc(sizeof(*commit->event),
 						GFP_KERNEL);
-- 
2.18.0.rc2