MIPS: Add support for XPA.

Add support for extended physical addressing (XPA) so that
32-bit platforms can access equal to or greater than 40 bits
of physical addresses.

NOTE:
      1) XPA and EVA are not the same and cannot be used
         simultaneously.
      2) If you configure your kernel for XPA, the PTEs
         and all address sizes become 64-bit.
      3) Your platform MUST have working HIGHMEM support.

Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9355/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/mm/init.c b/arch/mips/mm/init.c
index 448cde3..faa5c98 100644
--- a/arch/mips/mm/init.c
+++ b/arch/mips/mm/init.c
@@ -96,7 +96,7 @@
 	vaddr = __fix_to_virt(FIX_CMAP_END - idx);
 	pte = mk_pte(page, prot);
 #if defined(CONFIG_PHYS_ADDR_T_64BIT) && defined(CONFIG_CPU_MIPS32)
-	entrylo = pte.pte_high;
+	entrylo = pte_to_entrylo(pte.pte_high);
 #else
 	entrylo = pte_to_entrylo(pte_val(pte));
 #endif
@@ -106,6 +106,11 @@
 	write_c0_entryhi(vaddr & (PAGE_MASK << 1));
 	write_c0_entrylo0(entrylo);
 	write_c0_entrylo1(entrylo);
+#ifdef CONFIG_XPA
+	entrylo = (pte.pte_low & _PFNX_MASK);
+	writex_c0_entrylo0(entrylo);
+	writex_c0_entrylo1(entrylo);
+#endif
 	tlbidx = read_c0_wired();
 	write_c0_wired(tlbidx + 1);
 	write_c0_index(tlbidx);