drm/prime: introduce sg->pages/addr arrays helper

the ttm drivers need this currently, in order to get fault handling
working and efficient.

It also allows addrs to be NULL for devices like udl.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_prime.c

@@ -227,6 +227,42 @@ out:
 }
 EXPORT_SYMBOL(drm_prime_pages_to_sg);
 
+/* export an sg table into an array of pages and addresses
+   this is currently required by the TTM driver in order to do correct fault
+   handling */
+int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
+				     dma_addr_t *addrs, int max_pages)
+{
+	unsigned count;
+	struct scatterlist *sg;
+	struct page *page;
+	u32 len, offset;
+	int pg_index;
+	dma_addr_t addr;
+
+	pg_index = 0;
+	for_each_sg(sgt->sgl, sg, sgt->nents, count) {
+		len = sg->length;
+		offset = sg->offset;
+		page = sg_page(sg);
+		addr = sg_dma_address(sg);
+
+		while (len > 0) {
+			if (WARN_ON(pg_index >= max_pages))
+				return -1;
+			pages[pg_index] = page;
+			if (addrs)
+				addrs[pg_index] = addr;
+
+			page++;
+			addr += PAGE_SIZE;
+			len -= PAGE_SIZE;
+			pg_index++;
+		}
+	}
+	return 0;
+}
+EXPORT_SYMBOL(drm_prime_sg_to_page_addr_arrays);
 /* helper function to cleanup a GEM/prime object */
 void drm_prime_gem_destroy(struct drm_gem_object *obj, struct sg_table *sg)
 {

include/drm/drmP.h

@@ -1558,6 +1558,8 @@ extern int drm_prime_handle_to_fd_ioctl(struct drm_device *dev, void *data,
 extern int drm_prime_fd_to_handle_ioctl(struct drm_device *dev, void *data,
 					struct drm_file *file_priv);
 
+extern int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
+					    dma_addr_t *addrs, int max_pages);
 extern struct sg_table *drm_prime_pages_to_sg(struct page **pages, int nr_pages);
 extern void drm_prime_gem_destroy(struct drm_gem_object *obj, struct sg_table *sg);