introduce generic iommu_num_pages function

This patch introduces the generic iommu_num_pages function. It can be used by
a given memory area.

Signed-off-by: Joerg Roedel <[e-mail]>
Cc: "David S. Miller" <[e-mail]>
Cc: Richard Henderson <[e-mail]>
Cc: Ivan Kokshaysky <[e-mail]>
Cc: Benjamin Herrenschmidt <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: FUJITA Tomonori <[e-mail]>
Cc: Muli Ben-Yehuda <[e-mail]>
Cc: Dave Airlie <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/iommu-helper.h

···
 extern void iommu_area_free(unsigned long *map, unsigned long start,
 			    unsigned int nr);
 
+extern unsigned long iommu_num_pages(unsigned long addr, unsigned long len,
+				     unsigned long io_page_size);
+
 #endif

lib/iommu-helper.c

···
 	}
 }
 EXPORT_SYMBOL(iommu_area_free);
+
+unsigned long iommu_num_pages(unsigned long addr, unsigned long len,
+			      unsigned long io_page_size)
+{
+	unsigned long size = (addr & (io_page_size - 1)) + len;
+
+	return DIV_ROUND_UP(size, io_page_size);
+}
+EXPORT_SYMBOL(iommu_num_pages);