wayland: Add support for eglSwapInterval

The Wayland EGL platform now respects the eglSwapInterval value. The value is
clamped to either 0 or 1 because it is difficult (and probably not useful) to
sync to more than 1 redraw.

The main change is that if the swap interval is 0 then Mesa won't install a
frame callback so that eglSwapBuffers can be executed as often as necessary.
Instead it will do a sync request after the swap buffers. It will block for
sync complete event in get_back_bo instead of the frame callback. The
compositor is likely to send a release event while processing the new buffer
attach and this makes sure we will receive that before deciding whether to
allocate a new buffer.

If there are no buffers available then instead of returning with an error,
get_back_bo will now poll the compositor by repeatedly sending sync requests
every 10ms. This is a last resort and in theory this shouldn't happen because
there should be no reason for the compositor to hold on to more than three
buffers. That means whenever we attach the fourth buffer we should always get
an immediate release event which should come in with the notification for the
first sync request that we are throttled to.

When the compositor is directly scanning out from the application's buffer it
may end up holding on to three buffers. These are the one that is is currently
scanning out from, one that has been given to DRM as the next buffer to flip
to, and one that has been attached and will be given to DRM as soon as the
previous flip completes. When we attach a fourth buffer to the compositor it
should replace that third buffer so we should get a release event immediately
after that. This patch therefore also changes the number of buffer slots to 4
so that we can accomodate that situation.

If DRM eventually gets a way to cancel a pending page flip then the compositors
can be changed to only need to hold on to two buffers and this value can be
put back to 3.

This also moves the vblank configuration defines from platform_x11.c to the
common egl_dri2.h header so they can be shared by both platforms.

3 files changed, 119 insertions, 40 deletions

diff --git a/src/egl/drivers/dri2/egl_dri2.h b/src/egl/drivers/dri2/egl_dri2.h
index bbe5602ea59..522a0fd7c98 100644
--- a/src/egl/drivers/dri2/egl_dri2.h
+++ b/src/egl/drivers/dri2/egl_dri2.h
@@ -175,7 +175,7 @@ struct dri2_egl_surface
    struct wl_egl_window  *wl_win;
    int                    dx;
    int                    dy;
-   struct wl_callback    *frame_callback;
+   struct wl_callback    *throttle_callback;
    int			  format;
 #endif
 
@@ -195,7 +195,7 @@ struct dri2_egl_surface
 #endif
       int                 locked;
       int                 age;
-   } color_buffers[3], *back, *current;
+   } color_buffers[4], *back, *current;
 #endif
 
 #ifdef HAVE_ANDROID_PLATFORM
@@ -221,6 +221,12 @@ struct dri2_egl_image
    __DRIimage *dri_image;
 };
 
+/* From xmlpool/options.h, user exposed so should be stable */
+#define DRI_CONF_VBLANK_NEVER 0
+#define DRI_CONF_VBLANK_DEF_INTERVAL_0 1
+#define DRI_CONF_VBLANK_DEF_INTERVAL_1 2
+#define DRI_CONF_VBLANK_ALWAYS_SYNC 3
+
 /* standard typecasts */
 _EGL_DRIVER_STANDARD_TYPECASTS(dri2_egl)
 _EGL_DRIVER_TYPECAST(dri2_egl_image, _EGLImage, obj)
diff --git a/src/egl/drivers/dri2/platform_wayland.c b/src/egl/drivers/dri2/platform_wayland.c
index 87cb718ace1..e24ad9dac6e 100644
--- a/src/egl/drivers/dri2/platform_wayland.c
+++ b/src/egl/drivers/dri2/platform_wayland.c
@@ -183,8 +183,16 @@ dri2_create_window_surface(_EGLDriver *drv, _EGLDisplay *disp,
 			   _EGLConfig *conf, EGLNativeWindowType window,
 			   const EGLint *attrib_list)
 {
-   return dri2_create_surface(drv, disp, EGL_WINDOW_BIT, conf,
+   struct dri2_egl_display *dri2_dpy = dri2_egl_display(disp);
+   _EGLSurface *surf;
+
+   surf = dri2_create_surface(drv, disp, EGL_WINDOW_BIT, conf,
 			      window, attrib_list);
+
+   if (surf != NULL)
+      drv->API.SwapInterval(drv, disp, surf, dri2_dpy->default_swap_interval);
+
+   return surf;
 }
 
 /**
@@ -217,8 +225,8 @@ dri2_destroy_surface(_EGLDriver *drv, _EGLDisplay *disp, _EGLSurface *surf)
          dri2_dpy->dri2->releaseBuffer(dri2_dpy->dri_screen,
                                        dri2_surf->dri_buffers[i]);
 
-   if (dri2_surf->frame_callback)
-      wl_callback_destroy(dri2_surf->frame_callback);
+   if (dri2_surf->throttle_callback)
+      wl_callback_destroy(dri2_surf->throttle_callback);
 
    if (dri2_surf->base.Type == EGL_WINDOW_BIT) {
       dri2_surf->wl_win->private = NULL;
@@ -263,32 +271,25 @@ get_back_bo(struct dri2_egl_surface *dri2_surf)
       dri2_egl_display(dri2_surf->base.Resource.Display);
    int i;
 
-   if (dri2_surf->frame_callback == NULL) {
-      /* There might be a buffer release already queued that wasn't processed
-       */
-      wl_display_dispatch_queue_pending(dri2_dpy->wl_dpy, dri2_dpy->wl_queue);
-   } else {
-      /* We throttle to the frame callback here so that we can be sure to have
-       * received any release events before trying to decide whether to
-       * allocate a new buffer */
-      do {
-         if (wl_display_dispatch_queue(dri2_dpy->wl_dpy,
-                                       dri2_dpy->wl_queue) == -1)
-            return EGL_FALSE;
-      } while (dri2_surf->frame_callback != NULL);
-   }
-
+   /* We always want to throttle to some event (either a frame callback or
+    * a sync request) after the commit so that we can be sure the
+    * compositor has had a chance to handle it and send us a release event
+    * before we look for a free buffer */
+   while (dri2_surf->throttle_callback != NULL)
+      if (wl_display_dispatch_queue(dri2_dpy->wl_dpy,
+                                    dri2_dpy->wl_queue) == -1)
+         return EGL_FALSE;
 
    if (dri2_surf->back == NULL) {
       for (i = 0; i < ARRAY_SIZE(dri2_surf->color_buffers); i++) {
-         /* Get an unlocked buffer, preferrably one with a dri_buffer already
-          * allocated. */
-	 if (dri2_surf->color_buffers[i].locked)
+         /* Get an unlocked buffer, preferrably one with a dri_buffer
+          * already allocated. */
+         if (dri2_surf->color_buffers[i].locked)
             continue;
          if (dri2_surf->back == NULL)
-	    dri2_surf->back = &dri2_surf->color_buffers[i];
+            dri2_surf->back = &dri2_surf->color_buffers[i];
          else if (dri2_surf->back->dri_image == NULL)
-	    dri2_surf->back = &dri2_surf->color_buffers[i];
+            dri2_surf->back = &dri2_surf->color_buffers[i];
       }
    }
 
@@ -499,16 +500,18 @@ static const __DRIimageLoaderExtension image_loader_extension = {
 };
 
 static void
-wayland_frame_callback(void *data, struct wl_callback *callback, uint32_t time)
+wayland_throttle_callback(void *data,
+                          struct wl_callback *callback,
+                          uint32_t time)
 {
    struct dri2_egl_surface *dri2_surf = data;
 
-   dri2_surf->frame_callback = NULL;
+   dri2_surf->throttle_callback = NULL;
    wl_callback_destroy(callback);
 }
 
-static const struct wl_callback_listener frame_listener = {
-	wayland_frame_callback
+static const struct wl_callback_listener throttle_listener = {
+   wayland_throttle_callback
 };
 
 static void
@@ -585,11 +588,14 @@ dri2_swap_buffers_with_damage(_EGLDriver *drv,
       return EGL_FALSE;
    }
 
-   dri2_surf->frame_callback = wl_surface_frame(dri2_surf->wl_win->surface);
-   wl_callback_add_listener(dri2_surf->frame_callback,
-                            &frame_listener, dri2_surf);
-   wl_proxy_set_queue((struct wl_proxy *) dri2_surf->frame_callback,
-                      dri2_dpy->wl_queue);
+   if (draw->SwapInterval > 0) {
+      dri2_surf->throttle_callback =
+         wl_surface_frame(dri2_surf->wl_win->surface);
+      wl_callback_add_listener(dri2_surf->throttle_callback,
+                               &throttle_listener, dri2_surf);
+      wl_proxy_set_queue((struct wl_proxy *) dri2_surf->throttle_callback,
+                         dri2_dpy->wl_queue);
+   }
 
    dri2_surf->back->age = 1;
    dri2_surf->current = dri2_surf->back;
@@ -634,6 +640,19 @@ dri2_swap_buffers_with_damage(_EGLDriver *drv,
    (*dri2_dpy->flush->invalidate)(dri2_surf->dri_drawable);
 
    wl_surface_commit(dri2_surf->wl_win->surface);
+
+   /* If we're not waiting for a frame callback then we'll at least throttle
+    * to a sync callback so that we always give a chance for the compositor to
+    * handle the commit and send a release event before checking for a free
+    * buffer */
+   if (dri2_surf->throttle_callback == NULL) {
+      dri2_surf->throttle_callback = wl_display_sync(dri2_dpy->wl_dpy);
+      wl_callback_add_listener(dri2_surf->throttle_callback,
+                               &throttle_listener, dri2_surf);
+      wl_proxy_set_queue((struct wl_proxy *) dri2_surf->throttle_callback,
+                         dri2_dpy->wl_queue);
+   }
+
    wl_display_flush(dri2_dpy->wl_dpy);
 
    return EGL_TRUE;
@@ -877,6 +896,60 @@ static const struct wl_registry_listener registry_listener = {
    registry_handle_global_remove
 };
 
+static EGLBoolean
+dri2_swap_interval(_EGLDriver *drv,
+                   _EGLDisplay *disp,
+                   _EGLSurface *surf,
+                   EGLint interval)
+{
+   if (interval > surf->Config->MaxSwapInterval)
+      interval = surf->Config->MaxSwapInterval;
+   else if (interval < surf->Config->MinSwapInterval)
+      interval = surf->Config->MinSwapInterval;
+
+   surf->SwapInterval = interval;
+
+   return EGL_TRUE;
+}
+
+static void
+dri2_setup_swap_interval(struct dri2_egl_display *dri2_dpy)
+{
+   GLint vblank_mode = DRI_CONF_VBLANK_DEF_INTERVAL_1;
+
+   /* We can't use values greater than 1 on Wayland because we are using the
+    * frame callback to synchronise the frame and the only way we be sure to
+    * get a frame callback is to attach a new buffer. Therefore we can't just
+    * sit drawing nothing to wait until the next ‘n’ frame callbacks */
+
+   if (dri2_dpy->config)
+      dri2_dpy->config->configQueryi(dri2_dpy->dri_screen,
+                                     "vblank_mode", &vblank_mode);
+   switch (vblank_mode) {
+   case DRI_CONF_VBLANK_NEVER:
+      dri2_dpy->min_swap_interval = 0;
+      dri2_dpy->max_swap_interval = 0;
+      dri2_dpy->default_swap_interval = 0;
+      break;
+   case DRI_CONF_VBLANK_ALWAYS_SYNC:
+      dri2_dpy->min_swap_interval = 1;
+      dri2_dpy->max_swap_interval = 1;
+      dri2_dpy->default_swap_interval = 1;
+      break;
+   case DRI_CONF_VBLANK_DEF_INTERVAL_0:
+      dri2_dpy->min_swap_interval = 0;
+      dri2_dpy->max_swap_interval = 1;
+      dri2_dpy->default_swap_interval = 0;
+      break;
+   default:
+   case DRI_CONF_VBLANK_DEF_INTERVAL_1:
+      dri2_dpy->min_swap_interval = 0;
+      dri2_dpy->max_swap_interval = 1;
+      dri2_dpy->default_swap_interval = 1;
+      break;
+   }
+}
+
 EGLBoolean
 dri2_initialize_wayland(_EGLDriver *drv, _EGLDisplay *disp)
 {
@@ -893,8 +966,10 @@ dri2_initialize_wayland(_EGLDriver *drv, _EGLDisplay *disp)
    drv->API.DestroySurface = dri2_destroy_surface;
    drv->API.SwapBuffers = dri2_swap_buffers;
    drv->API.SwapBuffersWithDamageEXT = dri2_swap_buffers_with_damage;
+   drv->API.SwapInterval = dri2_swap_interval;
    drv->API.Terminate = dri2_terminate;
    drv->API.QueryBufferAge = dri2_query_buffer_age;
+
    drv->API.CreateWaylandBufferFromImageWL =
       dri2_create_wayland_buffer_from_image_wl;
 
@@ -953,9 +1028,13 @@ dri2_initialize_wayland(_EGLDriver *drv, _EGLDisplay *disp)
    dri2_dpy->extensions[3] = &use_invalidate.base;
    dri2_dpy->extensions[4] = NULL;
 
+   dri2_dpy->swap_available = EGL_TRUE;
+
    if (!dri2_create_screen(disp))
       goto cleanup_driver;
 
+   dri2_setup_swap_interval(dri2_dpy);
+
    /* The server shouldn't advertise WL_DRM_CAPABILITY_PRIME if the driver
     * doesn't have createImageFromFds, since we're using the same driver on
     * both sides.  We don't want crash if that happens anyway, so fall back to
diff --git a/src/egl/drivers/dri2/platform_x11.c b/src/egl/drivers/dri2/platform_x11.c
index 04cb62b41d3..d3397d49639 100644
--- a/src/egl/drivers/dri2/platform_x11.c
+++ b/src/egl/drivers/dri2/platform_x11.c
@@ -41,12 +41,6 @@
 
 #include "egl_dri2.h"
 
-/* From xmlpool/options.h, user exposed so should be stable */
-#define DRI_CONF_VBLANK_NEVER 0
-#define DRI_CONF_VBLANK_DEF_INTERVAL_0 1
-#define DRI_CONF_VBLANK_DEF_INTERVAL_1 2
-#define DRI_CONF_VBLANK_ALWAYS_SYNC 3
-
 static void
 swrastCreateDrawable(struct dri2_egl_display * dri2_dpy,
                      struct dri2_egl_surface * dri2_surf,