drm/ttm: add io_mem_pfn callback

This allows the driver to handle io_mem mappings on their own.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
index 0b1ce05..fa07be1 100644
--- a/include/drm/ttm/ttm_bo_api.h
+++ b/include/drm/ttm/ttm_bo_api.h
@@ -711,6 +711,17 @@ extern int ttm_fbdev_mmap(struct vm_area_struct *vma,
 			  struct ttm_buffer_object *bo);
 
 /**
+ * ttm_bo_default_iomem_pfn - get a pfn for a page offset
+ *
+ * @bo: the BO we need to look up the pfn for
+ * @page_offset: offset inside the BO to look up.
+ *
+ * Calculate the PFN for iomem based mappings during page fault
+ */
+unsigned long ttm_bo_default_io_mem_pfn(struct ttm_buffer_object *bo,
+				        unsigned long page_offset);
+
+/**
  * ttm_bo_mmap - mmap out of the ttm device address space.
  *
  * @filp:      filp as input from the mmap method.