diff --git a/common/hw-gfx-gma-pipe_setup.ads b/common/hw-gfx-gma-pipe_setup.ads
index 3ecb6dd..960e70f 100644
--- a/common/hw-gfx-gma-pipe_setup.ads
+++ b/common/hw-gfx-gma-pipe_setup.ads
@@ -51,10 +51,22 @@
       FB       : Framebuffer_Type;
       Cursor   : Cursor_Type);
 
-   procedure Scaler_Available (Available : out Boolean; Pipe : Pipe_Index);
+   type Scaler_Reservation is private;
+   Null_Scaler_Reservation : constant Scaler_Reservation;
+   procedure Reserve_Scaler
+     (Success     :    out Boolean;
+      Reservation : in out Scaler_Reservation;
+      Pipe        : in     Pipe_Index);
 
 private
 
+   type Scaler_Reservation is record
+      Reserved : Boolean;
+      Pipe     : Pipe_Index;
+   end record;
+   Null_Scaler_Reservation : constant Scaler_Reservation :=
+     (Reserved => False, Pipe => Pipe_Index'First);
+
    subtype WM_Levels is Natural range 0 .. 7;
    type PLANE_WM_Type is array (WM_Levels) of Registers.Registers_Index;