powerpc/mm/radix: Update Radix tree size as per ISA 3.0

ISA 3.0 updated it to be encoded as Radix tree size = 2^(RTS + 31). We
have it encoded as 2^(RTS + 28). Add a helper with the correct encoding
and use it instead of opencoding.

Fixes: 2bfd65e45e ("powerpc/mm/radix: Add radix callbacks for early init routines")
Reviewed-by: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/mm/mmu_context_book3s64.c

@@ -65,7 +65,7 @@ static int radix__init_new_context(struct mm_struct *mm, int index)
 	/*
 	 * set the process table entry,
 	 */
-	rts_field = 3ull << PPC_BITLSHIFT(2);
+	rts_field = radix__get_tree_size();
 	process_tb[index].prtb0 = cpu_to_be64(rts_field | __pa(mm->pgd) | RADIX_PGD_INDEX_SIZE);
 	return 0;
 }

arch/powerpc/mm/pgtable-radix.c

@@ -160,9 +160,8 @@ redo:
 	process_tb = early_alloc_pgtable(1UL << PRTB_SIZE_SHIFT);
 	/*
 	 * Fill in the process table.
-	 * we support 52 bits, hence 52-28 = 24, 11000
 	 */
-	rts_field = 3ull << PPC_BITLSHIFT(2);
+	rts_field = radix__get_tree_size();
 	process_tb->prtb0 = cpu_to_be64(rts_field | __pa(init_mm.pgd) | RADIX_PGD_INDEX_SIZE);
 	/*
 	 * Fill in the partition table. We are suppose to use effective address
@@ -176,10 +175,8 @@ redo:
 static void __init radix_init_partition_table(void)
 {
 	unsigned long rts_field;
-	/*
-	 * we support 52 bits, hence 52-28 = 24, 11000
-	 */
-	rts_field = 3ull << PPC_BITLSHIFT(2);
+
+	rts_field = radix__get_tree_size();
 
 	BUILD_BUG_ON_MSG((PATB_SIZE_SHIFT > 24), "Partition table size too large.");
 	partition_tb = early_alloc_pgtable(1UL << PATB_SIZE_SHIFT);