[Bugfix][Hardware][AMD] Consolidate FP8 min/max values helper function (#31106)

Signed-off-by: c0de128 <kevin.mckay@outlook.com>
Signed-off-by: Kevin McKay <kevin@example.com>
Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

tests/kernels/quantization/test_fp8_min_max_helper.py

@@ -0,0 +1,65 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""
+Unit tests for the get_fp8_min_max() helper function.
+
+These tests verify the FP8 min/max value logic for both standard
+and fnuz (ROCm MI300) dtype handling.
+"""
+
+from unittest.mock import patch
+
+import pytest
+import torch
+
+from vllm.model_executor.layers.quantization.utils.quant_utils import (
+    get_fp8_min_max,
+)
+
+
+class TestGetFp8MinMax:
+    """Test cases for get_fp8_min_max() function."""
+
+    @patch("vllm.model_executor.layers.quantization.utils.quant_utils.current_platform")
+    def test_standard_fp8_platform(self, mock_platform):
+        """Test that standard FP8 platform uses PyTorch's finfo values."""
+        mock_platform.is_fp8_fnuz.return_value = False
+        mock_platform.fp8_dtype.return_value = torch.float8_e4m3fn
+
+        fp8_min, fp8_max = get_fp8_min_max()
+        finfo = torch.finfo(torch.float8_e4m3fn)
+
+        # Standard FP8 max is 448.0 for e4m3fn
+        assert fp8_max == finfo.max, f"Expected finfo.max={finfo.max}, got {fp8_max}"
+        assert fp8_min == finfo.min, f"Expected finfo.min={finfo.min}, got {fp8_min}"
+
+    @patch("vllm.model_executor.layers.quantization.utils.quant_utils.current_platform")
+    def test_fnuz_platform_returns_224(self, mock_platform):
+        """Test that fnuz platform returns 224.0."""
+        mock_platform.is_fp8_fnuz.return_value = True
+
+        fp8_min, fp8_max = get_fp8_min_max()
+
+        # fnuz on ROCm MI300 should return 224.0, not 240.0
+        assert fp8_max == 224.0, f"Expected 224.0 for fnuz platform, got {fp8_max}"
+        assert fp8_min == -224.0, f"Expected -224.0 for fnuz platform, got {fp8_min}"
+
+    @patch("vllm.model_executor.layers.quantization.utils.quant_utils.current_platform")
+    def test_non_fnuz_platform_uses_finfo(self, mock_platform):
+        """Test that non-fnuz platform uses finfo values."""
+        mock_platform.is_fp8_fnuz.return_value = False
+        mock_platform.fp8_dtype.return_value = torch.float8_e4m3fn
+
+        fp8_min, fp8_max = get_fp8_min_max()
+        finfo = torch.finfo(torch.float8_e4m3fn)
+
+        assert fp8_max == finfo.max, (
+            f"Non-fnuz platform should use finfo.max={finfo.max}, got {fp8_max}"
+        )
+        assert fp8_min == finfo.min, (
+            f"Non-fnuz platform should use finfo.min={finfo.min}, got {fp8_min}"
+        )
+
+
+if __name__ == "__main__":
+    pytest.main([__file__, "-v"])