drm/gem: Add evict() callback to drm_gem_object_funcs

Add new common evict() callback to drm_gem_object_funcs and corresponding
drm_gem_object_evict() helper. This is a first step on a way to providing
common GEM-shrinker API for DRM drivers.
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Suggested-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://lore.kernel.org/all/20230108210445.3948344-4-dmitry.osipenko@collabora.com/

drivers/gpu/drm/drm_gem.c

@@ -1459,3 +1459,21 @@ drm_gem_lru_scan(struct drm_gem_lru *lru, unsigned nr_to_scan,
 	return freed;
 }
 EXPORT_SYMBOL(drm_gem_lru_scan);
+
+/**
+ * drm_gem_evict - helper to evict backing pages for a GEM object
+ * @obj: obj in question
+ */
+int drm_gem_evict(struct drm_gem_object *obj)
+{
+	dma_resv_assert_held(obj->resv);
+
+	if (!dma_resv_test_signaled(obj->resv, DMA_RESV_USAGE_READ))
+		return -EBUSY;
+
+	if (obj->funcs->evict)
+		return obj->funcs->evict(obj);
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_gem_evict);

include/drm/drm_gem.h

@@ -164,6 +164,16 @@ struct drm_gem_object_funcs {
 	 */
 	int (*mmap)(struct drm_gem_object *obj, struct vm_area_struct *vma);
 
+	/**
+	 * @evict:
+	 *
+	 * Evicts gem object out from memory. Used by the drm_gem_object_evict()
+	 * helper. Returns 0 on success, -errno otherwise.
+	 *
+	 * This callback is optional.
+	 */
+	int (*evict)(struct drm_gem_object *obj);
+
 	/**
 	 * @vm_ops:
 	 *
@@ -479,4 +489,6 @@ void drm_gem_lru_move_tail(struct drm_gem_lru *lru, struct drm_gem_object *obj);
 unsigned long drm_gem_lru_scan(struct drm_gem_lru *lru, unsigned nr_to_scan,
 			       bool (*shrink)(struct drm_gem_object *obj));
 
+int drm_gem_evict(struct drm_gem_object *obj);
+
 #endif /* __DRM_GEM_H__ */