Raise an error when trying to use SD Cascade Decoder with dtype bfloat16 and torch < 2.2 (#7244)

update

src/diffusers/pipelines/stable_cascade/pipeline_stable_cascade.py

@@ -19,7 +19,7 @@ from transformers import CLIPTextModel, CLIPTokenizer
 
 from ...models import StableCascadeUNet
 from ...schedulers import DDPMWuerstchenScheduler
-from ...utils import logging, replace_example_docstring
+from ...utils import is_torch_version, logging, replace_example_docstring
 from ...utils.torch_utils import randn_tensor
 from ..pipeline_utils import DiffusionPipeline, ImagePipelineOutput
 from ..wuerstchen.modeling_paella_vq_model import PaellaVQModel
@@ -361,6 +361,8 @@ class StableCascadeDecoderPipeline(DiffusionPipeline):
         device = self._execution_device
         dtype = self.decoder.dtype
         self._guidance_scale = guidance_scale
+        if is_torch_version("<", "2.2.0") and dtype == torch.bfloat16:
+            raise ValueError("`StableCascadeDecoderPipeline` requires torch>=2.2.0 when using `torch.bfloat16` dtype.")
 
         # 1. Check inputs. Raise error if not correct
         self.check_inputs(