powerpc/8xx: Refactor calculation of number of entries per PTE in page tables

On 8xx, the number of entries occupied by a PTE in the page tables
depends on the size of the page. At the time being, this calculation
is done in two places: in pte_update() and in set_huge_pte_at()

Refactor this calculation into a helper called
number_of_cells_per_pte(). For the time being, the val param is
unused. It will be used by following patch.

Instead of opencoding is_hugepd(), use hugepd_ok() with a forward
declaration.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/f6ea2483c2c389567b007945948f704d18cfaeea.1598862623.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/nohash/32/pgtable.h

@@ -227,6 +227,17 @@ static inline void pmd_clear(pmd_t *pmdp)
  */
 #ifdef CONFIG_PPC_8xx
 static pmd_t *pmd_off(struct mm_struct *mm, unsigned long addr);
+static int hugepd_ok(hugepd_t hpd);
+
+static int number_of_cells_per_pte(pmd_t *pmd, pte_basic_t val, int huge)
+{
+	if (!huge)
+		return PAGE_SIZE / SZ_4K;
+	else if (hugepd_ok(*((hugepd_t *)pmd)))
+		return 1;
+	else
+		return SZ_512K / SZ_4K;
+}
 
 static inline pte_basic_t pte_update(struct mm_struct *mm, unsigned long addr, pte_t *p,
 				     unsigned long clr, unsigned long set, int huge)
@@ -237,12 +248,7 @@ static inline pte_basic_t pte_update(struct mm_struct *mm, unsigned long addr, p
 	int num, i;
 	pmd_t *pmd = pmd_off(mm, addr);
 
-	if (!huge)
-		num = PAGE_SIZE / SZ_4K;
-	else if ((pmd_val(*pmd) & _PMD_PAGE_MASK) != _PMD_PAGE_8M)
-		num = SZ_512K / SZ_4K;
-	else
-		num = 1;
+	num = number_of_cells_per_pte(pmd, new, huge);
 
 	for (i = 0; i < num; i++, entry++, new += SZ_4K)
 		*entry = new;

arch/powerpc/mm/pgtable.c

@@ -266,8 +266,7 @@ void set_huge_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep, pte_
 	pmd_t *pmd = pmd_off(mm, addr);
 	pte_basic_t val;
 	pte_basic_t *entry = &ptep->pte;
-	int num = is_hugepd(*((hugepd_t *)pmd)) ? 1 : SZ_512K / SZ_4K;
-	int i;
+	int num, i;
 
 	/*
 	 * Make sure hardware valid bit is not set. We don't do
@@ -280,6 +279,9 @@ void set_huge_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep, pte_
 	pte = set_pte_filter(pte);
 
 	val = pte_val(pte);
+
+	num = number_of_cells_per_pte(pmd, val, 1);
+
 	for (i = 0; i < num; i++, entry++, val += SZ_4K)
 		*entry = val;
 }