[OOT] Add OOT support for linear kernel. (#37989)

Signed-off-by: menogrey <1299267905@qq.com>

tests/kernels/quantization/test_scaled_mm_kernel_selection.py

@@ -7,15 +7,21 @@ Run `pytest tests/kernels/quantization/test_scaled_mm_kernel_selection.py`.
 
 import inspect
 from abc import ABC
+from unittest.mock import patch
 
 import pytest
+import torch
 
 from vllm.model_executor.kernels.linear import (
     AiterInt8ScaledMMLinearKernel,
     CPUInt8ScaledMMLinearKernel,
+    Int8ScaledMMLinearKernel,
     Int8ScaledMMLinearLayerConfig,
     ScaledMMLinearKernel,
+    init_int8_linear_kernel,
+    register_linear_kernel,
 )
+from vllm.platforms import PlatformEnum
 
 pytestmark = pytest.mark.cpu_test
 
@@ -85,3 +91,39 @@ def test_cpu_kernel_accepts_all_configs():
         assert can_impl, (
             f"CPUInt8ScaledMMLinearKernel should accept config {config}: {reason}"
         )
+
+
+class OOTInt8ScaledMMLinearKernel(Int8ScaledMMLinearKernel):
+    @classmethod
+    def is_supported(
+        cls, compute_capability: int | None = None
+    ) -> tuple[bool, str | None]:
+        return True, None
+
+    @classmethod
+    def can_implement(cls, c: Int8ScaledMMLinearLayerConfig) -> tuple[bool, str | None]:
+        return True, None
+
+    def process_weights_after_loading(self, layer: torch.nn.Module) -> None:
+        pass
+
+    def apply_weights(
+        self,
+        layer: torch.nn.Module,
+        x: torch.Tensor,
+        bias: torch.Tensor | None = None,
+    ) -> torch.Tensor:
+        pass
+
+
+@patch("vllm.model_executor.kernels.linear.current_platform")
+def test_register_oot_linear_kernel(platform_mock):
+    """Test that the linear kernel registration works correctly."""
+    platform_mock._enum = PlatformEnum.OOT
+    register_linear_kernel(OOTInt8ScaledMMLinearKernel, PlatformEnum.OOT, "int8")
+
+    kernel = init_int8_linear_kernel(True, True, True, "module")
+
+    assert isinstance(kernel, OOTInt8ScaledMMLinearKernel), (
+        "init_int8_linear_kernel should return an instance of the registered kernel"
+    )