[PATCH] drm/atomic: skip ww_acquire_done() for legacy paths

[Rob Clark]

The addition of ww_acquire_done() call to mark the point where all locks
should already be held, added in:

  commit 992cbf19b32900efa17850b9fa0031fd623edd4d
  Author:     Daniel Vetter <daniel.vetter at ffwll.ch>
  AuthorDate: Thu Aug 6 15:06:40 2015 +0200

      drm/atomic: Call ww_acquire_done after check phase is complete

missed the case that legacy paths (which are already called between
drm_modeset_lock_all()/unlock_all()) re-use the single acquire ctx, even
if there are multiple atomic updates.  For example, restore_fbdev_mode()
clearing rotation properties individually on each plane.

Inki already sent a patch which completely removed the ww_acquire_done()
call, but I think this is less ideal (since it is a nice debugging
feature of ww_mutex to confirm that everyone is following the rules).
So instead, just skip the call only in the special legacy-path case.

Reported-by: Inki Dae <inki.dae at samsung.com>
Tested-by: Bjorn Andersson <bjorn.andersson at sonymobile.com>
Signed-off-by: Rob Clark <robdclark at gmail.com>
---
 drivers/gpu/drm/drm_atomic.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index 1066e4b..b90068c 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -1230,8 +1230,15 @@ int drm_atomic_check_only(struct drm_atomic_state *state)
 		}
 	}
 
-	if (ret == 0)
-		ww_acquire_done(&state->acquire_ctx->ww_ctx);
+	if (ret == 0) {
+		/* in legacy paths, there can be multiple atomic updates,
+		 * such as drm_mode_plane_set_obj_prop(), which happen
+		 * under a single drm_modeset_lock_all().  In the legacy
+		 * paths, skip marking acquire-done lest we anger ww-mutex:
+		 */
+		if (state->acquire_ctx != dev->mode_config.acquire_ctx)
+			ww_acquire_done(&state->acquire_ctx->ww_ctx);
+	}
 
 	return ret;
 }
-- 
2.4.3