backend/native: Only disable dmabuf screen cast when not hw accelerated

We now only enable DMA buffer based PipeWire screen casting if a
format/modifier has been negotiated. This practically means a consumer
is aware about what is needed, and we should not try to predict that it
uses the DMA buffer the right way (i.e. not mmap:ing directly).

However, in case we're not hardware accelerated, we never want to
attempt to use DMA buffer screen sharing, as we want to avoid
compositing into a DMA buffer on such hardware as doing so can be very
slow.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2086>

data/org.gnome.mutter.gschema.xml.in

@@ -4,8 +4,7 @@
     <value nick="scale-monitor-framebuffer" value="1"/>
     <value nick="kms-modifiers" value="2"/>
     <value nick="rt-scheduler" value="4"/>
-    <value nick="dma-buf-screen-sharing" value="8"/>
+    <value nick="autoclose-xwayland" value="8"/>
-    <value nick="autoclose-xwayland" value="16"/>
   </flags>
 
   <schema id="org.gnome.mutter" path="/org/gnome/mutter/"
@@ -139,11 +138,6 @@
         • “rt-scheduler”              — makes mutter request a low priority
                                         real-time scheduling. Requires a restart.
 
-        • “dma-buf-screen-sharing”    — enables DMA buffered screen sharing. This
-                                        is already enabled by default when using
-                                        the i915 driver, but disabled for 
-                                        everything else. Requires a restart.
-
         • “autoclose-xwayland”        — automatically terminates Xwayland if all
                                         relevant X11 clients are gone.
                                         Requires a restart.

src/backends/meta-settings-private.h

@@ -34,8 +34,7 @@ typedef enum _MetaExperimentalFeature
   META_EXPERIMENTAL_FEATURE_SCALE_MONITOR_FRAMEBUFFER = (1 << 0),
   META_EXPERIMENTAL_FEATURE_KMS_MODIFIERS  = (1 << 1),
   META_EXPERIMENTAL_FEATURE_RT_SCHEDULER = (1 << 2),
-  META_EXPERIMENTAL_FEATURE_DMA_BUF_SCREEN_SHARING = (1 << 3),
+  META_EXPERIMENTAL_FEATURE_AUTOCLOSE_XWAYLAND  = (1 << 3),
-  META_EXPERIMENTAL_FEATURE_AUTOCLOSE_XWAYLAND  = (1 << 4),
 } MetaExperimentalFeature;
 
 typedef enum _MetaXwaylandExtension

src/backends/meta-settings.c

@@ -294,8 +294,6 @@ experimental_features_handler (GVariant *features_variant,
         feature = META_EXPERIMENTAL_FEATURE_KMS_MODIFIERS;
       else if (g_str_equal (feature_str, "rt-scheduler"))
         feature = META_EXPERIMENTAL_FEATURE_RT_SCHEDULER;
-      else if (g_str_equal (feature_str, "dma-buf-screen-sharing"))
-        feature = META_EXPERIMENTAL_FEATURE_DMA_BUF_SCREEN_SHARING;
       else if (g_str_equal (feature_str, "autoclose-xwayland"))
         feature = META_EXPERIMENTAL_FEATURE_AUTOCLOSE_XWAYLAND;
 

src/backends/native/meta-backend-native.c

@@ -158,40 +158,15 @@ static void
 maybe_disable_screen_cast_dma_bufs (MetaBackendNative *native)
 {
   MetaBackend *backend = META_BACKEND (native);
-  MetaSettings *settings = meta_backend_get_settings (backend);
   MetaRenderer *renderer = meta_backend_get_renderer (backend);
-  MetaRendererNative *renderer_native = META_RENDERER_NATIVE (renderer);
   MetaScreenCast *screen_cast = meta_backend_get_screen_cast (backend);
-  MetaGpuKms *primary_gpu;
-  MetaKmsDevice *kms_device;
-  const char *driver_name;
-  static const char *enable_dma_buf_drivers[] = {
-    "i915",
-    NULL,
-  };
 
-  primary_gpu = meta_renderer_native_get_primary_gpu (renderer_native);
+  if (!meta_renderer_is_hardware_accelerated (renderer))
-  if (!primary_gpu)
     {
-      g_message ("Disabling DMA buffer screen sharing (surfaceless)");
+      g_message ("Disabling DMA buffer screen sharing "
-      goto disable_dma_bufs;
+                 "(not hardware accelerated)");
+      meta_screen_cast_disable_dma_bufs (screen_cast);
     }
-
-  kms_device = meta_gpu_kms_get_kms_device (primary_gpu);
-  driver_name = meta_kms_device_get_driver_name (kms_device);
-
-  if (g_strv_contains (enable_dma_buf_drivers, driver_name))
-    return;
-
-  if (meta_settings_is_experimental_feature_enabled (settings,
-        META_EXPERIMENTAL_FEATURE_DMA_BUF_SCREEN_SHARING))
-    return;
-
-  g_message ("Disabling DMA buffer screen sharing for driver '%s'.",
-             driver_name);
-
-disable_dma_bufs:
-  meta_screen_cast_disable_dma_bufs (screen_cast);
 }
 #endif /* HAVE_REMOTE_DESKTOP */