m68k: mm: Unify Motorola MMU page setup

Seeing how there are 5 copies of this magic code, one of which is
unexplainably different, unify and document things.
Suggested-by: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Greg Ungerer <gerg@linux-m68k.org>
Tested-by: Michael Schmitz <schmitzmic@gmail.com>
Tested-by: Greg Ungerer <gerg@linux-m68k.org>
Link: https://lore.kernel.org/r/20200131125403.597688427@infradead.orgSigned-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/include/asm/motorola_pgalloc.h

@@ -5,6 +5,9 @@
 #include <asm/tlb.h>
 #include <asm/tlbflush.h>
 
+extern void mmu_page_ctor(void *page);
+extern void mmu_page_dtor(void *page);
+
 extern pmd_t *get_pointer_table(void);
 extern int free_pointer_table(pmd_t *);
 
@@ -13,25 +16,21 @@ static inline pte_t *pte_alloc_one_kernel(struct mm_struct *mm)
 	pte_t *pte;
 
 	pte = (pte_t *)__get_free_page(GFP_KERNEL|__GFP_ZERO);
-	if (pte) {
-		__flush_page_to_ram(pte);
-		flush_tlb_kernel_page(pte);
-		nocache_page(pte);
-	}
+	if (pte)
+		mmu_page_ctor(pte);
 
 	return pte;
 }
 
 static inline void pte_free_kernel(struct mm_struct *mm, pte_t *pte)
 {
-	cache_page(pte);
+	mmu_page_dtor(pte);
 	free_page((unsigned long) pte);
 }
 
 static inline pgtable_t pte_alloc_one(struct mm_struct *mm)
 {
 	struct page *page;
-	pte_t *pte;
 
 	page = alloc_pages(GFP_KERNEL|__GFP_ZERO, 0);
 	if(!page)
@@ -41,18 +40,16 @@ static inline pgtable_t pte_alloc_one(struct mm_struct *mm)
 		return NULL;
 	}
 
-	pte = kmap(page);
-	__flush_page_to_ram(pte);
-	flush_tlb_kernel_page(pte);
-	nocache_page(pte);
+	mmu_page_ctor(kmap(page));
 	kunmap(page);
+
 	return page;
 }
 
 static inline void pte_free(struct mm_struct *mm, pgtable_t page)
 {
 	pgtable_pte_page_dtor(page);
-	cache_page(kmap(page));
+	mmu_page_dtor(kmap(page));
 	kunmap(page);
 	__free_page(page);
 }
@@ -61,7 +58,7 @@ static inline void __pte_free_tlb(struct mmu_gather *tlb, pgtable_t page,
 				  unsigned long address)
 {
 	pgtable_pte_page_dtor(page);
-	cache_page(kmap(page));
+	mmu_page_dtor(kmap(page));
 	kunmap(page);
 	__free_page(page);
 }

arch/m68k/mm/memory.c

@@ -77,8 +77,7 @@ pmd_t *get_pointer_table (void)
 		if (!(page = (void *)get_zeroed_page(GFP_KERNEL)))
 			return NULL;
 
-		flush_tlb_kernel_page(page);
-		nocache_page(page);
+		mmu_page_ctor(page);
 
 		new = PD_PTABLE(page);
 		PD_MARKBITS(new) = 0xfe;
@@ -112,7 +111,7 @@ int free_pointer_table (pmd_t *ptable)
 	if (PD_MARKBITS(dp) == 0xff) {
 		/* all tables in page are free, free page */
 		list_del(dp);
-		cache_page((void *)page);
+		mmu_page_dtor((void *)page);
 		free_page (page);
 		return 1;
 	} else if (ptable_list.next != dp) {

arch/m68k/mm/motorola.c

@@ -45,6 +45,28 @@ unsigned long mm_cachebits;
 EXPORT_SYMBOL(mm_cachebits);
 #endif
 
+
+/*
+ * Motorola 680x0 user's manual recommends using uncached memory for address
+ * translation tables.
+ *
+ * Seeing how the MMU can be external on (some of) these chips, that seems like
+ * a very important recommendation to follow. Provide some helpers to combat
+ * 'variation' amongst the users of this.
+ */
+
+void mmu_page_ctor(void *page)
+{
+	__flush_page_to_ram(page);
+	flush_tlb_kernel_page(page);
+	nocache_page(page);
+}
+
+void mmu_page_dtor(void *page)
+{
+	cache_page(page);
+}
+
 /* size of memory already mapped in head.S */
 extern __initdata unsigned long m68k_init_mapped_size;
 
@@ -60,9 +82,7 @@ static pte_t * __init kernel_page_table(void)
 		      __func__, PAGE_SIZE, PAGE_SIZE);
 
 	clear_page(ptablep);
-	__flush_page_to_ram(ptablep);
-	flush_tlb_kernel_page(ptablep);
-	nocache_page(ptablep);
+	mmu_page_ctor(ptablep);
 
 	return ptablep;
 }
@@ -106,9 +126,7 @@ static pmd_t * __init kernel_ptr_table(void)
 			      __func__, PAGE_SIZE, PAGE_SIZE);
 
 		clear_page(last_pgtable);
-		__flush_page_to_ram(last_pgtable);
-		flush_tlb_kernel_page(last_pgtable);
-		nocache_page(last_pgtable);
+		mmu_page_ctor(last_pgtable);
 	}
 
 	return last_pgtable;