mips: mm: convert __flush_dcache_pages() to __flush_dcache_folio_pages()

Let's make it clearer that we are operating within a single folio by
providing both the folio and the page.

This implies that for flush_dcache_folio() we'll now avoid one more
page->folio lookup, and that we can safely drop the "nth_page" usage.

While at it, drop the "extern" from the function declaration.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: David Hildenbrand <[e-mail]>
Cc: Thomas Bogendoerfer <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

arch/mips/include/asm/cacheflush.h

···
 extern void (*flush_cache_range)(struct vm_area_struct *vma,
 	unsigned long start, unsigned long end);
 extern void (*flush_cache_page)(struct vm_area_struct *vma, unsigned long page, unsigned long pfn);
-extern void __flush_dcache_pages(struct page *page, unsigned int nr);
+void __flush_dcache_folio_pages(struct folio *folio, struct page *page, unsigned int nr);
 
 #define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE 1
 static inline void flush_dcache_folio(struct folio *folio)
 {
 	if (cpu_has_dc_aliases)
-		__flush_dcache_pages(&folio->page, folio_nr_pages(folio));
+		__flush_dcache_folio_pages(folio, folio_page(folio, 0),
+					   folio_nr_pages(folio));
 	else if (!cpu_has_ic_fills_f_dc)
 		folio_set_dcache_dirty(folio);
 }
···
 
 static inline void flush_dcache_page(struct page *page)
 {
+	struct folio *folio = page_folio(page);
+
 	if (cpu_has_dc_aliases)
-		__flush_dcache_pages(page, 1);
+		__flush_dcache_folio_pages(folio, page, 1);
 	else if (!cpu_has_ic_fills_f_dc)
-		folio_set_dcache_dirty(page_folio(page));
+		folio_set_dcache_dirty(folio);
 }
 
 #define flush_dcache_mmap_lock(mapping)		do { } while (0)

arch/mips/mm/cache.c

···
 	return 0;
 }
 
-void __flush_dcache_pages(struct page *page, unsigned int nr)
+void __flush_dcache_folio_pages(struct folio *folio, struct page *page,
+		unsigned int nr)
 {
-	struct folio *folio = page_folio(page);
 	struct address_space *mapping = folio_flush_mapping(folio);
 	unsigned long addr;
 	unsigned int i;
···
 	 * get faulted into the tlb (and thus flushed) anyways.
 	 */
 	for (i = 0; i < nr; i++) {
-		addr = (unsigned long)kmap_local_page(nth_page(page, i));
+		addr = (unsigned long)kmap_local_page(page + i);
 		flush_data_cache_page(addr);
 		kunmap_local((void *)addr);
 	}
 }
-EXPORT_SYMBOL(__flush_dcache_pages);
+EXPORT_SYMBOL(__flush_dcache_folio_pages);
 
 void __flush_anon_page(struct page *page, unsigned long vmaddr)
 {