drm/ttm/radeon/nouveau: Kill the bo lock in favour of a bo device fence_lock

The bo lock used only to protect the bo sync object members, and since it
is a per bo lock, fencing a buffer list will see a lot of locks and unlocks.
Replace it with a per-device lock that protects the sync object members on
*all* bos. Reading and setting these members will always be very quick, so
the risc of heavy lock contention is microscopic. Note that waiting for
sync objects will always take place outside of this lock.

The bo device fence lock will eventually be replaced with a seqlock /
rcu mechanism so we can determine that a bo is idle under a
rcu / read seqlock.

However this change will allow us to batch fencing and unreserving of
buffers with a minimal amount of locking.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jerome Glisse <j.glisse@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/drivers/gpu/drm/ttm/ttm_execbuf_util.c b/drivers/gpu/drm/ttm/ttm_execbuf_util.c
index 7dcc6470e2f5..c3a2100bace6 100644
--- a/drivers/gpu/drm/ttm/ttm_execbuf_util.c
+++ b/drivers/gpu/drm/ttm/ttm_execbuf_util.c
@@ -203,14 +203,15 @@ void ttm_eu_fence_buffer_objects(struct list_head *list, void *sync_obj)
 
         list_for_each_entry(entry, list, head) {
                 struct ttm_buffer_object *bo = entry->bo;
-                struct ttm_bo_driver *driver = bo->bdev->driver;
+                struct ttm_bo_device *bdev = bo->bdev;
+                struct ttm_bo_driver *driver = bdev->driver;
                 void *old_sync_obj;
 
-                spin_lock(&bo->lock);
+                spin_lock(&bdev->fence_lock);
                 old_sync_obj = bo->sync_obj;
                 bo->sync_obj = driver->sync_obj_ref(sync_obj);
                 bo->sync_obj_arg = entry->new_sync_obj_arg;
-                spin_unlock(&bo->lock);
+                spin_unlock(&bdev->fence_lock);
                 ttm_bo_unreserve(bo);
                 entry->reserved = false;
                 if (old_sync_obj)