[Mesa-dev] [PATCH 2/3] dri3: Flush and wait for X rendering upon glXWaitX()

[Chris Wilson]

glXWaitX() is supposed to be a synchronisation point with rendering via
the X server. Currently, it only tries to keep front buffered rendering
synchronised, but we also need to flush all rendering to shared pixmaps
as well (which, for example, are used as texture sources by compositors).

Note that this assumes that Xorg continues to flush all rendering upon
triggering XSync rather than rendering to the drawable associated with
the XSync. If Xorg does implement more fine-grained synchronisation
requests (like for DRI2), we will need to ensure all tfp are also
synchronisation following the glXWaitX().

References: https://bugs.freedesktop.org/show_bug.cgi?id=97914
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 src/loader/loader_dri3_helper.c | 44 ++++++++++++++++++++++++++++++++++++++++-
 src/loader/loader_dri3_helper.h |  3 +++
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/src/loader/loader_dri3_helper.c b/src/loader/loader_dri3_helper.c
index ca02e97..f4f6d53 100644
--- a/src/loader/loader_dri3_helper.c
+++ b/src/loader/loader_dri3_helper.c
@@ -113,6 +113,11 @@ loader_dri3_drawable_fini(struct loader_dri3_drawable *draw)
          dri3_free_render_buffer(draw, draw->buffers[i]);
    }
 
+   if (draw->sync_fence) {
+      xcb_sync_destroy_fence(draw->conn, draw->sync_fence);
+      xshmfence_unmap_shm(draw->shm_fence);
+   }
+
    if (draw->special_event) {
       xcb_void_cookie_t cookie =
          xcb_present_select_input_checked(draw->conn, draw->eid, draw->drawable,
@@ -549,7 +554,19 @@ loader_dri3_wait_x(struct loader_dri3_drawable *draw)
    struct loader_dri3_buffer *front;
    __DRIcontext *dri_context;
 
-   if (draw == NULL || !draw->have_fake_front)
+   if (draw == NULL)
+      return;
+
+   if (draw->sync_fence) {
+      xshmfence_reset(draw->shm_fence);
+
+      xcb_sync_trigger_fence(draw->conn, draw->sync_fence);
+      xcb_flush(draw->conn);
+
+      xshmfence_await(draw->shm_fence);
+   }
+
+   if (!draw->have_fake_front)
       return;
 
    front = dri3_fake_front_buffer(draw);
@@ -943,6 +960,29 @@ no_shm_fence:
    return NULL;
 }
 
+static void
+dri3_attach_sync(struct loader_dri3_drawable *draw)
+{
+   int fence_fd;
+
+   fence_fd = xshmfence_alloc_shm();
+   if (fence_fd < 0)
+      return;
+
+   draw->shm_fence = xshmfence_map_shm(fence_fd);
+   if (draw->shm_fence == NULL) {
+      close(fence_fd);
+      return;
+   }
+
+   draw->sync_fence = xcb_generate_id(draw->conn);
+   xcb_dri3_fence_from_fd(draw->conn,
+                          draw->drawable,
+                          draw->sync_fence,
+                          false,
+                          fence_fd);
+}
+
 /** loader_dri3_update_drawable
  *
  * Called the first time we use the drawable and then
@@ -1032,6 +1072,8 @@ dri3_update_drawable(__DRIdrawable *driDrawable,
          xcb_unregister_for_special_event(draw->conn, draw->special_event);
          draw->special_event = NULL;
       }
+
+      dri3_attach_sync(draw);
    }
    dri3_flush_present_events(draw);
    return true;
diff --git a/src/loader/loader_dri3_helper.h b/src/loader/loader_dri3_helper.h
index 1d1f15e..dab15b6 100644
--- a/src/loader/loader_dri3_helper.h
+++ b/src/loader/loader_dri3_helper.h
@@ -156,6 +156,9 @@ struct loader_dri3_drawable {
    xcb_gcontext_t gc;
    xcb_special_event_t *special_event;
 
+   xcb_sync_fence_t sync_fence;
+   struct xshmfence *shm_fence;
+
    bool first_init;
 
    struct loader_dri3_extensions *ext;
-- 
2.9.3