drm/gem-framebuffer: Use dma_buf from GEM object instance

Avoid dereferencing struct drm_gem_object.import_attach for the
imported dma-buf. The dma_buf field in the GEM object instance refers
to the same buffer. Prepares to make import_attach optional.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Anusha Srivatsa <asrivats@redhat.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250226172457.217725-8-tzimmermann@suse.de

Author: Thomas Zimmermann

drivers/gpu/drm/drm_gem_framebuffer_helper.c

@@ -419,7 +419,6 @@ EXPORT_SYMBOL(drm_gem_fb_vunmap);
 static void __drm_gem_fb_end_cpu_access(struct drm_framebuffer *fb, enum dma_data_direction dir,
 					unsigned int num_planes)
 {
-	struct dma_buf_attachment *import_attach;
 	struct drm_gem_object *obj;
 	int ret;
 
@@ -428,10 +427,9 @@ static void __drm_gem_fb_end_cpu_access(struct drm_framebuffer *fb, enum dma_dat
 		obj = drm_gem_fb_get_obj(fb, num_planes);
 		if (!obj)
 			continue;
-		import_attach = obj->import_attach;
 		if (!drm_gem_is_imported(obj))
 			continue;
-		ret = dma_buf_end_cpu_access(import_attach->dmabuf, dir);
+		ret = dma_buf_end_cpu_access(obj->dma_buf, dir);
 		if (ret)
 			drm_err(fb->dev, "dma_buf_end_cpu_access(%u, %d) failed: %d\n",
 				ret, num_planes, dir);
@@ -454,7 +452,6 @@ static void __drm_gem_fb_end_cpu_access(struct drm_framebuffer *fb, enum dma_dat
  */
 int drm_gem_fb_begin_cpu_access(struct drm_framebuffer *fb, enum dma_data_direction dir)
 {
-	struct dma_buf_attachment *import_attach;
 	struct drm_gem_object *obj;
 	unsigned int i;
 	int ret;
@@ -465,10 +462,9 @@ int drm_gem_fb_begin_cpu_access(struct drm_framebuffer *fb, enum dma_data_direct
 			ret = -EINVAL;
 			goto err___drm_gem_fb_end_cpu_access;
 		}
-		import_attach = obj->import_attach;
 		if (!drm_gem_is_imported(obj))
 			continue;
-		ret = dma_buf_begin_cpu_access(import_attach->dmabuf, dir);
+		ret = dma_buf_begin_cpu_access(obj->dma_buf, dir);
 		if (ret)
 			goto err___drm_gem_fb_end_cpu_access;
 	}