drm/gem-ttm-helper: Provide helper for struct drm_driver.dumb_map_offset

Provides an implementation of struct drm_driver.dumb_map_offset that
can be used by TTM-based GEM drivers.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20210408140139.27731-2-tzimmermann@suse.de

drivers/gpu/drm/drm_gem_ttm_helper.c

@@ -114,5 +114,38 @@ int drm_gem_ttm_mmap(struct drm_gem_object *gem,
 }
 EXPORT_SYMBOL(drm_gem_ttm_mmap);
 
+/**
+ * drm_gem_ttm_dumb_map_offset() - Implements struct &drm_driver.dumb_map_offset
+ * @file:	DRM file pointer.
+ * @dev:	DRM device.
+ * @handle:	GEM handle
+ * @offset:	Returns the mapping's memory offset on success
+ *
+ * Provides an implementation of struct &drm_driver.dumb_map_offset for
+ * TTM-based GEM drivers. TTM allocates the offset internally and
+ * drm_gem_ttm_dumb_map_offset() returns it for dumb-buffer implementations.
+ *
+ * See struct &drm_driver.dumb_map_offset.
+ *
+ * Returns:
+ * 0 on success, or a negative errno code otherwise.
+ */
+int drm_gem_ttm_dumb_map_offset(struct drm_file *file, struct drm_device *dev,
+				uint32_t handle, uint64_t *offset)
+{
+	struct drm_gem_object *gem;
+
+	gem = drm_gem_object_lookup(file, handle);
+	if (!gem)
+		return -ENOENT;
+
+	*offset = drm_vma_node_offset_addr(&gem->vma_node);
+
+	drm_gem_object_put(gem);
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_gem_ttm_dumb_map_offset);
+
 MODULE_DESCRIPTION("DRM gem ttm helpers");
 MODULE_LICENSE("GPL");

include/drm/drm_gem_ttm_helper.h

@@ -5,8 +5,8 @@
 
 #include <linux/kernel.h>
 
-#include <drm/drm_gem.h>
 #include <drm/drm_device.h>
+#include <drm/drm_gem.h>
 #include <drm/ttm/ttm_bo_api.h>
 #include <drm/ttm/ttm_bo_driver.h>
 
@@ -24,4 +24,7 @@ void drm_gem_ttm_vunmap(struct drm_gem_object *gem,
 int drm_gem_ttm_mmap(struct drm_gem_object *gem,
 		     struct vm_area_struct *vma);
 
+int drm_gem_ttm_dumb_map_offset(struct drm_file *file, struct drm_device *dev,
+				uint32_t handle, uint64_t *offset);
+
 #endif