Make Gemma and Gemma 2 accept inputs_embeds like Gemma 3 (#36787)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

tests/models/language/generation/test_common.py

@@ -3,6 +3,8 @@
 
 import pytest
 import torch
+from packaging.version import Version
+from transformers import __version__ as TRANSFORMERS_VERSION
 
 from vllm.platforms import current_platform
 
@@ -151,6 +153,16 @@ def test_models(
             if prompt_embeds is not None:
                 embed = hf_model.model.get_input_embeddings()(token_ids)
 
+                if "gemma" in model.lower() and (
+                    Version(TRANSFORMERS_VERSION) < Version("5.3.0.dev0")
+                ):
+                    # For Gemma 1/2 models with Transformers 5.4.0+, the prompt
+                    # embeddings are normalised in `get_prompt_embeddings`,
+                    # like Gemma 3. For older versions, we need to manually normalise.
+                    embed_scale = hf_model.config.hidden_size**0.5
+                    normalizer = torch.tensor(embed_scale, dtype=embed.dtype)
+                    embed *= normalizer
+
                 # MiniCPM models apply scale_emb to embeddings internally.
                 # vLLM expects pre-scaled embeddings when using inputs_embeds.
                 if model in EMBED_SCALING_MODELS: