diff -urN ref/arch/alpha/kernel/core_tsunami.c 2.4.5pre4aa1/arch/alpha/kernel/core_tsunami.c
--- ref/arch/alpha/kernel/core_tsunami.c	Tue May 22 18:16:47 2001
+++ 2.4.5pre4aa1/arch/alpha/kernel/core_tsunami.c	Tue May 22 18:20:18 2001
@@ -278,6 +278,16 @@
 #define FN __FUNCTION__
 
 static void __init
+tsunami_monster_window_enable(tsunami_pchip * pchip)
+{
+	volatile unsigned long * csr = &pchip->pctl.csr;
+
+	*csr |= pctl_m_mwin;
+	mb();
+	*csr;
+}
+
+static void __init
 tsunami_init_one_pchip(tsunami_pchip *pchip, int index)
 {
 	struct pci_controller *hose;
@@ -383,6 +393,9 @@
 		pchip->wsba[3].csr = 0;
 
 	tsunami_pci_tbi(hose, 0, -1);
+
+	/* Enable the Monster Window to make DAC pci64 possible. */
+	tsunami_monster_window_enable(pchip);
 }
 
 void __init
diff -urN ref/include/asm-alpha/core_tsunami.h 2.4.5pre4aa1/include/asm-alpha/core_tsunami.h
--- ref/include/asm-alpha/core_tsunami.h	Tue May 22 18:16:47 2001
+++ 2.4.5pre4aa1/include/asm-alpha/core_tsunami.h	Tue May 22 17:46:16 2001
@@ -275,6 +275,9 @@
 /* The IO address space is larger than 0xffff */
 #define TSUNAMI_IO_SPACE	(TSUNAMI_CONF(0) - TSUNAMI_IO(0))
 
+/* Offset between ram physical addresses and pci64 DAC bus addresses */
+#define TSUNAMI_DAC_OFFSET	(1UL << 40)
+
 /*
  * Data structure for handling TSUNAMI machine checks:
  */