drm/atomic-helper: Simplify commit tracking locking

The crtc->commit_lock only protects commit_list and commit_entry. If
we chase the pointer from the drm_atomic_state update structure, then
we don't need any locks (since we hold a reference already).

Simplify the locking accordingly.

Noticed while reviewing a patch from Boris.

Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170621091627.30837-1-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_atomic_helper.c

@@ -1715,9 +1715,7 @@ void drm_atomic_helper_commit_hw_done(struct drm_atomic_state *old_state)
 
 		/* backend must have consumed any event by now */
 		WARN_ON(new_crtc_state->event);
-		spin_lock(&crtc->commit_lock);
 		complete_all(&commit->hw_done);
-		spin_unlock(&crtc->commit_lock);
 	}
 }
 EXPORT_SYMBOL(drm_atomic_helper_commit_hw_done);
@@ -1746,7 +1744,6 @@ void drm_atomic_helper_commit_cleanup_done(struct drm_atomic_state *old_state)
 		if (WARN_ON(!commit))
 			continue;
 
-		spin_lock(&crtc->commit_lock);
 		complete_all(&commit->cleanup_done);
 		WARN_ON(!try_wait_for_completion(&commit->hw_done));
 
@@ -1756,8 +1753,6 @@ void drm_atomic_helper_commit_cleanup_done(struct drm_atomic_state *old_state)
 		if (try_wait_for_completion(&commit->flip_done))
 			goto del_commit;
 
-		spin_unlock(&crtc->commit_lock);
-
 		/* We must wait for the vblank event to signal our completion
 		 * before releasing our reference, since the vblank work does
 		 * not hold a reference of its own. */
@@ -1767,8 +1762,8 @@ void drm_atomic_helper_commit_cleanup_done(struct drm_atomic_state *old_state)
 			DRM_ERROR("[CRTC:%d:%s] flip_done timed out\n",
 				  crtc->base.id, crtc->name);
 
-		spin_lock(&crtc->commit_lock);
 del_commit:
+		spin_lock(&crtc->commit_lock);
 		list_del(&commit->commit_entry);
 		spin_unlock(&crtc->commit_lock);
 	}