drm: add func to get max iomem address v2

it will be used to check if the driver needs swiotlb
v2: Don't use inline, instead, move function to drm_memory.c (Michel Daenzer <michel@daenzer.net>)
Signed-off-by: Chunming Zhou <david1.zhou@amd.com>
Reviewed-by: Monk Liu <monk.liu@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180209024410.1469-1-david1.zhou@amd.com

drivers/gpu/drm/drm_memory.c

@@ -149,3 +149,16 @@ void drm_legacy_ioremapfree(struct drm_local_map *map, struct drm_device *dev)
 		iounmap(map->handle);
 }
 EXPORT_SYMBOL(drm_legacy_ioremapfree);
+
+u64 drm_get_max_iomem(void)
+{
+	struct resource *tmp;
+	u64 max_iomem = 0;
+
+	for (tmp = iomem_resource.child; tmp; tmp = tmp->sibling) {
+		max_iomem = max(max_iomem,  tmp->end);
+	}
+
+	return max_iomem;
+}
+EXPORT_SYMBOL(drm_get_max_iomem);

include/drm/drm_cache.h

@@ -38,6 +38,8 @@
 void drm_clflush_pages(struct page *pages[], unsigned long num_pages);
 void drm_clflush_sg(struct sg_table *st);
 void drm_clflush_virt_range(void *addr, unsigned long length);
+u64 drm_get_max_iomem(void);
+
 
 static inline bool drm_arch_can_wc_memory(void)
 {