From c9725d3b78211e08bcdcd3f7aabff68fc01c7ab6 Mon Sep 17 00:00:00 2001
From: Andreas Schaafsma <andreas@subsonics.nl>
Date: Thu, 3 Sep 2026 10:10:52 +0200
Subject: [PATCH] mutter tearing patches

---
 .../drivebystation-nix/default.nix            |  3 +-
 .../mutter-50-tearing-compat.patch            | 51 +++++++++++++++++++
 .../drivebystation-nix/mutter-tearing.nix     | 50 ++++++++++++++++++
 3 files changed, 103 insertions(+), 1 deletion(-)
 create mode 100644 systems/x86_64-linux/drivebystation-nix/mutter-50-tearing-compat.patch
 create mode 100644 systems/x86_64-linux/drivebystation-nix/mutter-tearing.nix

diff --git a/systems/x86_64-linux/drivebystation-nix/default.nix b/systems/x86_64-linux/drivebystation-nix/default.nix
index b269b5e..2e3bd88 100644
--- a/systems/x86_64-linux/drivebystation-nix/default.nix
+++ b/systems/x86_64-linux/drivebystation-nix/default.nix
@@ -34,6 +34,7 @@ in
   # inherit system;
   imports = [
     ./configuration.nix
+    ./mutter-tearing.nix
     ./video.nix
     inputs.aagl.nixosModules.default
   ];
@@ -222,4 +223,4 @@ in
       systemd.targets.hibernate.enable = false;
       systemd.targets.hybrid-sleep.enable = false;
     };
-}
\ No newline at end of file
+}
diff --git a/systems/x86_64-linux/drivebystation-nix/mutter-50-tearing-compat.patch b/systems/x86_64-linux/drivebystation-nix/mutter-50-tearing-compat.patch
new file mode 100644
index 0000000..bcec785
--- /dev/null
+++ b/systems/x86_64-linux/drivebystation-nix/mutter-50-tearing-compat.patch
@@ -0,0 +1,51 @@
+diff --git a/src/compositor/meta-compositor-view-native.c b/src/compositor/meta-compositor-view-native.c
+--- a/src/compositor/meta-compositor-view-native.c
++++ b/src/compositor/meta-compositor-view-native.c
+@@ -289,9 +289,11 @@ find_scanout_candidate (MetaCompositorView  *compositor_view,
+     return FALSE;
+ 
+   if (!meta_stage_view_is_cursor_overlay_inhibited (view) &&
++      !meta_onscreen_native_is_tearing_enabled (
++        META_ONSCREEN_NATIVE (framebuffer)) &&
+       surface_actor_has_overlapping_cursor_overlays (compositor,
+                                                      compositor_view,
+                                                      surface_actor))
+     {
+       meta_topic (META_DEBUG_RENDER,
+                   "No direct scanout candidate: overlapping software cursors");
+diff --git a/src/meson.build b/src/meson.build
+--- a/src/meson.build
++++ b/src/meson.build
+@@ -1077,5 +1077,6 @@ wayland_protocols = [
+   ['single-pixel-buffer', 'staging', 1, ],
+   ['tablet', 'stable', 2, ],
++  ['tearing-control', 'staging', 1, ],
+   ['text-input-unstable-v3', 'private', ],
+   ['viewporter', 'stable', ],
+   ['xdg-activation', 'staging', 1, ],
+diff --git a/src/wayland/meta-wayland-dma-buf.c b/src/wayland/meta-wayland-dma-buf.c
+--- a/src/wayland/meta-wayland-dma-buf.c
++++ b/src/wayland/meta-wayland-dma-buf.c
+@@ -630,11 +630,22 @@ has_modifier (GArray   *modifiers,
+ }
+ 
+ #ifdef HAVE_NATIVE_BACKEND
++static gboolean
++async_supports_modifier (MetaKmsPlane *plane,
++                         uint32_t      drm_format,
++                         uint64_t      drm_modifier)
++{
++  GArray *async_modifiers =
++    meta_kms_plane_get_async_modifiers_for_format (plane, drm_format);
++  return async_modifiers && has_modifier (async_modifiers, drm_modifier);
++}
++
+ static gboolean
+ crtc_supports_modifier (MetaCrtcKms *crtc_kms,
+                         uint32_t     drm_format,
+-                        uint64_t     drm_modifier)
++                        uint64_t     drm_modifier,
++                        gboolean     is_async)
+ {
+   MetaKmsPlane *plane = meta_crtc_kms_get_assigned_primary_plane (crtc_kms);
+   GArray *crtc_modifiers;
diff --git a/systems/x86_64-linux/drivebystation-nix/mutter-tearing.nix b/systems/x86_64-linux/drivebystation-nix/mutter-tearing.nix
new file mode 100644
index 0000000..f1c26ed
--- /dev/null
+++ b/systems/x86_64-linux/drivebystation-nix/mutter-tearing.nix
@@ -0,0 +1,50 @@
+{ lib, pkgs, ... }:
+
+let
+  # GNOME/mutter!3797, pinned because the MR is still under development.
+  mutterTearingRevision = "a8d56d423edde9e6d76f6b9cab663d82c65cf1a2";
+  mutterTearingPatch = pkgs.fetchurl {
+    url = "https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3797.diff";
+    hash = "sha256-3up5PsHX+BSQRKb9JS5bnJLPaTGmvV55M18tKkepIng=";
+  };
+in
+{
+  nixpkgs.overlays = [
+    (final: prev: {
+      mutter = prev.mutter.overrideAttrs (old: {
+        pname = "mutter-tearing";
+
+        # The MR currently targets Mutter 51. Apply it to the packaged Mutter
+        # 50 source, then resolve the four small context conflicts separately.
+        prePatch = ''
+          ${old.prePatch or ""}
+
+          set +e
+          patch --batch -p1 --forward < ${mutterTearingPatch}
+          mr_status=$?
+          set -e
+
+          if [ "$mr_status" -ne 0 ]; then
+            reject_count="$(find . -name '*.rej' -type f | wc -l)"
+            if [ "$reject_count" -ne 3 ]; then
+              echo "Unexpected number of Mutter !3797 rejects: $reject_count" >&2
+              exit 1
+            fi
+          fi
+
+          patch --batch -p1 --forward < ${./mutter-50-tearing-compat.patch}
+          find . -name '*.rej' -type f -delete
+        '';
+
+        passthru = (old.passthru or { }) // {
+          tearingMr = 3797;
+          tearingRevision = mutterTearingRevision;
+        };
+      });
+    })
+  ];
+
+  # Mutter keeps tearing support behind an experimental runtime switch.
+  environment.sessionVariables.MUTTER_DEBUG_EXPERIMENTAL_FEATURES =
+    lib.mkDefault "tearing";
+}