[mutter] screen-cast: Enable DMA buffers only for i915

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 6c0440697d0647a950ec46ba6e6047801c2313ef
Author: Jonas Ådahl <jadahl gmail com>
Date:   Mon Sep 14 11:36:25 2020 +0200

    screen-cast: Enable DMA buffers only for i915
    
    Seems DMA buffer based interprocess buffer sharing is more broken than
    not, so for now only enable it when using the i915 driver.
    
    For example vmwgfx, qxl and radeon, it results in mmap() failing to mmap the
    memory region. Other drivers, e.g. amdgpu will function, but may hit
    very slow memory download paths, resulting in worse performance.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1442

 src/backends/native/meta-backend-native.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)
---
diff --git a/src/backends/native/meta-backend-native.c b/src/backends/native/meta-backend-native.c
index fc68fe917b..1b7c8e0581 100644
--- a/src/backends/native/meta-backend-native.c
+++ b/src/backends/native/meta-backend-native.c
@@ -349,12 +349,12 @@ maybe_disable_screen_cast_dma_bufs (MetaBackendNative *native)
   MetaBackend *backend = META_BACKEND (native);
   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 *disable_dma_buf_drivers[] = {
-    "qxl",
-    "vmwgfx",
+  static const char *enable_dma_buf_drivers[] = {
+    "i915",
     NULL,
   };
 
@@ -362,16 +362,13 @@ maybe_disable_screen_cast_dma_bufs (MetaBackendNative *native)
   kms_device = meta_gpu_kms_get_kms_device (primary_gpu);
   driver_name = meta_kms_device_get_driver_name (kms_device);
 
-  if (g_strv_contains (disable_dma_buf_drivers, driver_name))
-    {
-      MetaScreenCast *screen_cast = meta_backend_get_screen_cast (backend);
+  if (g_strv_contains (enable_dma_buf_drivers, driver_name))
+    return;
 
-      g_message ("The '%s' driver doesn't support DMA buffer screen sharing, disabling.",
-                 driver_name);
+  g_message ("Disabling DMA buffer screen sharing for driver '%s'.",
+             driver_name);
 
-      meta_screen_cast_disable_dma_bufs (screen_cast);
-      return;
-    }
+  meta_screen_cast_disable_dma_bufs (screen_cast);
 }
 #endif /* HAVE_REMOTE_DESKTOP */