[Bugfix] Revert max_prompt_len validation for decoder-only models. (vllm-project#16741)

Signed-off-by: David Heineman <david@davidheineman.com>
Signed-off-by: Yang Wang <elainewy@meta.com>

Author: davidheineman

vllm/engine/llm_engine.py

@@ -2062,7 +2062,7 @@ def _validate_model_input(
                 raise ValueError(f"The {prompt_type} prompt cannot be empty")
 
         max_prompt_len = self.model_config.max_model_len
-        if len(prompt_ids) >= max_prompt_len:
+        if len(prompt_ids) > max_prompt_len:
             if prompt_type == "encoder" and model_config.is_multimodal_model:
                 mm_registry = self.input_preprocessor.mm_registry
                 mm_processor = mm_registry.create_processor(

vllm/v1/engine/processor.py

@@ -354,7 +354,7 @@ def _validate_model_input(
             raise ValueError(f"Token id {max_input_id} is out of vocabulary")
 
         max_prompt_len = self.model_config.max_model_len
-        if len(prompt_ids) >= max_prompt_len:
+        if len(prompt_ids) > max_prompt_len:
             if prompt_type == "encoder" and model_config.is_multimodal_model:
                 mm_registry = self.input_preprocessor.mm_registry
                 mm_processor = mm_registry.create_processor(