drm/syncobj: Add a callback mechanism for replace_fence (v3)

It is useful in certain circumstances to know when the fence is replaced
in a syncobj.  Specifically, it may be useful to know when the fence
goes from NULL to something valid.  This does make syncobj_replace_fence
a little more expensive because it has to take a lock but, in the common
case where there is no callback list, it spends a very short amount of
time inside the lock.

v2:
 - Don't lock in drm_syncobj_fence_get.  We only really need to lock
   around fence_replace to make the callback work.
v3:
 - Fix the cb_list comment to make kbuild happy

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>

diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
index 4e8563c36d6e484359d829e4c90f6a2fc712276c..bade497b3f1dea295db853fac7b635620542215c 100644 (file)
--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -80,6 +80,46 @@ struct drm_syncobj *drm_syncobj_find(struct drm_file *file_private,
 }
 EXPORT_SYMBOL(drm_syncobj_find);
 
+static void drm_syncobj_add_callback_locked(struct drm_syncobj *syncobj,
+                                           struct drm_syncobj_cb *cb,
+                                           drm_syncobj_func_t func)
+{
+       cb->func = func;
+       list_add_tail(&cb->node, &syncobj->cb_list);
+}
+
+/**
+ * drm_syncobj_add_callback - adds a callback to syncobj::cb_list
+ * @syncobj: Sync object to which to add the callback
+ * @cb: Callback to add
+ * @func: Func to use when initializing the drm_syncobj_cb struct
+ *
+ * This adds a callback to be called next time the fence is replaced
+ */
+void drm_syncobj_add_callback(struct drm_syncobj *syncobj,
+                             struct drm_syncobj_cb *cb,
+                             drm_syncobj_func_t func)
+{
+       spin_lock(&syncobj->lock);
+       drm_syncobj_add_callback_locked(syncobj, cb, func);
+       spin_unlock(&syncobj->lock);
+}
+EXPORT_SYMBOL(drm_syncobj_add_callback);
+
+/**
+ * drm_syncobj_add_callback - removes a callback to syncobj::cb_list
+ * @syncobj: Sync object from which to remove the callback
+ * @cb: Callback to remove
+ */
+void drm_syncobj_remove_callback(struct drm_syncobj *syncobj,
+                                struct drm_syncobj_cb *cb)
+{
+       spin_lock(&syncobj->lock);
+       list_del_init(&cb->node);
+       spin_unlock(&syncobj->lock);
+}
+EXPORT_SYMBOL(drm_syncobj_remove_callback);
+
 /**
  * drm_syncobj_replace_fence - replace fence in a sync object.
  * @syncobj: Sync object to replace fence in
@@ -91,10 +131,24 @@ void drm_syncobj_replace_fence(struct drm_syncobj *syncobj,
                               struct dma_fence *fence)
 {
        struct dma_fence *old_fence;
+       struct drm_syncobj_cb *cur, *tmp;
 
        if (fence)
                dma_fence_get(fence);
-       old_fence = xchg(&syncobj->fence, fence);
+
+       spin_lock(&syncobj->lock);
+
+       old_fence = syncobj->fence;
+       syncobj->fence = fence;
+
+       if (fence != old_fence) {
+               list_for_each_entry_safe(cur, tmp, &syncobj->cb_list, node) {
+                       list_del_init(&cur->node);
+                       cur->func(syncobj, cur);
+               }
+       }
+
+       spin_unlock(&syncobj->lock);
 
        dma_fence_put(old_fence);
 }
@@ -130,7 +184,7 @@ void drm_syncobj_free(struct kref *kref)
        struct drm_syncobj *syncobj = container_of(kref,
                                                   struct drm_syncobj,
                                                   refcount);
-       dma_fence_put(syncobj->fence);
+       drm_syncobj_replace_fence(syncobj, NULL);
        kfree(syncobj);
 }
 EXPORT_SYMBOL(drm_syncobj_free);
@@ -146,6 +200,8 @@ static int drm_syncobj_create(struct drm_file *file_private,
                return -ENOMEM;
 
        kref_init(&syncobj->refcount);
+       INIT_LIST_HEAD(&syncobj->cb_list);
+       spin_lock_init(&syncobj->lock);
 
        idr_preload(GFP_KERNEL);
        spin_lock(&file_private->syncobj_table_lock);

diff --git a/include/drm/drm_syncobj.h b/include/drm/drm_syncobj.h
index ce94d14c50878bce13a1f3b58cc524e0351e397f..c00fee5398224735311fa7581bfe62481cf4ffea 100644 (file)
--- a/include/drm/drm_syncobj.h
+++ b/include/drm/drm_syncobj.h
@@ -28,6 +28,8 @@
 
 #include "linux/dma-fence.h"
 
+struct drm_syncobj_cb;
+
 /**
  * struct drm_syncobj - sync object.
  *
@@ -43,8 +45,21 @@ struct drm_syncobj {
        /**
         * @fence:
         * NULL or a pointer to the fence bound to this object.
+        *
+        * This field should not be used directly.  Use drm_syncobj_fence_get
+        * and drm_syncobj_replace_fence instead.
         */
        struct dma_fence *fence;
+       /**
+        * @cb_list:
+        * List of callbacks to call when the fence gets replaced
+        */
+       struct list_head cb_list;
+       /**
+        * @lock:
+        * locks cb_list and write-locks fence.
+        */
+       spinlock_t lock;
        /**
         * @file:
         * a file backing for this syncobj.
@@ -52,6 +67,25 @@ struct drm_syncobj {
        struct file *file;
 };
 
+typedef void (*drm_syncobj_func_t)(struct drm_syncobj *syncobj,
+                                  struct drm_syncobj_cb *cb);
+
+/**
+ * struct drm_syncobj_cb - callback for drm_syncobj_add_callback
+ * @node: used by drm_syncob_add_callback to append this struct to
+ *       syncobj::cb_list
+ * @func: drm_syncobj_func_t to call
+ *
+ * This struct will be initialized by drm_syncobj_add_callback, additional
+ * data can be passed along by embedding drm_syncobj_cb in another struct.
+ * The callback will get called the next time drm_syncobj_replace_fence is
+ * called.
+ */
+struct drm_syncobj_cb {
+       struct list_head node;
+       drm_syncobj_func_t func;
+};
+
 void drm_syncobj_free(struct kref *kref);
 
 /**
@@ -91,6 +125,11 @@ drm_syncobj_fence_get(struct drm_syncobj *syncobj)
 
 struct drm_syncobj *drm_syncobj_find(struct drm_file *file_private,
                                     u32 handle);
+void drm_syncobj_add_callback(struct drm_syncobj *syncobj,
+                             struct drm_syncobj_cb *cb,
+                             drm_syncobj_func_t func);
+void drm_syncobj_remove_callback(struct drm_syncobj *syncobj,
+                                struct drm_syncobj_cb *cb);
 void drm_syncobj_replace_fence(struct drm_syncobj *syncobj,
                               struct dma_fence *fence);
 int drm_syncobj_find_fence(struct drm_file *file_private,