virgl: Add VIRGL_RENDERER_ASYNC_FENCE_CB flag

The flag allows fence callback to be executed directly from the
fence polling thread. It requires the `write_fence` callback
provided by the user to be thread-safe.

The `virgl_renderer_poll()` method no longer needs to be called
by the user if that flag is used.

v2: set VKR_RENDERER_ASYNC_FENCE_CB as well (by olv)

Signed-off-by: Louis-Francis Ratté-Boulianne <lfrb@collabora.com>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
Reviewed-by: Ryan Neph <ryanneph@google.com> (v1)

src/virglrenderer.c

@@ -667,6 +667,8 @@ int virgl_renderer_init(void *cookie, int flags, struct virgl_renderer_callbacks
 
       if (flags & VIRGL_RENDERER_THREAD_SYNC)
          renderer_flags |= VREND_USE_THREAD_SYNC;
+      if (flags & VIRGL_RENDERER_ASYNC_FENCE_CB)
+         renderer_flags |= VREND_USE_ASYNC_FENCE_CB;
       if (flags & VIRGL_RENDERER_USE_EXTERNAL_BLOB)
          renderer_flags |= VREND_USE_EXTERNAL_BLOB;
 
@@ -680,6 +682,8 @@ int virgl_renderer_init(void *cookie, int flags, struct virgl_renderer_callbacks
       uint32_t vkr_flags = 0;
       if (flags & VIRGL_RENDERER_THREAD_SYNC)
          vkr_flags |= VKR_RENDERER_THREAD_SYNC;
+      if (flags & VIRGL_RENDERER_ASYNC_FENCE_CB)
+         vkr_flags |= VKR_RENDERER_ASYNC_FENCE_CB;
 
       ret = vkr_renderer_init(vkr_flags);
       if (ret)

src/virglrenderer.h

@@ -98,6 +98,13 @@ struct virgl_renderer_callbacks {
  */
 #define VIRGL_RENDERER_NO_VIRGL      (1 << 7)
 
+/*
+ * Used in conjonction with VIRGL_RENDERER_THREAD_SYNC;
+ * write_fence callback is executed directly from the polling thread. When enabled,
+ * virgl_renderer_get_poll_fd should not be used to watch for retired fences.
+ */
+#define VIRGL_RENDERER_ASYNC_FENCE_CB (1 << 8)
+
 #endif /* VIRGL_RENDERER_UNSTABLE_APIS */
 
 VIRGL_EXPORT int virgl_renderer_init(void *cookie, int flags, struct virgl_renderer_callbacks *cb);