Arm backend: Add experimental support for new TOSAQuantizer

backends/arm/quantizer/TARGETS

@@ -17,9 +17,11 @@ runtime.python_library(
     deps = [
         ":arm_quantizer_utils",
         ":quantization_annotator",
+        ":quantizer_support",
         "//executorch/backends/arm:constants",
         "//executorch/backends/arm:ethosu",
         "//executorch/backends/arm:vgf",
+        "//executorch/backends/cortex_m/quantizer:quantizer",
         "//executorch/backends/arm/tosa:specification",
         "//executorch/backends/arm:arm_compile_spec",
         "//caffe2:torch",
@@ -48,6 +50,16 @@ runtime.python_library(
     ],
 )
 
+runtime.python_library(
+    name = "quantizer_support",
+    srcs = ["quantizer_support.py"],
+    deps = [
+        ":quantization_annotator",
+        "//caffe2:torch",
+        "//executorch/backends/cortex_m/quantizer:quantizer",
+    ],
+)
+
 runtime.python_library(
     name = "lib",
     srcs = ["__init__.py"],

backends/arm/quantizer/__init__.py

@@ -11,17 +11,34 @@
 """
 
 from .quantization_config import QuantizationConfig  # noqa  # usort: skip
-from .arm_quantizer import (  # noqa
-    EthosUQuantizer,
-    get_symmetric_a16w8_quantization_config,
-    get_symmetric_quantization_config,
-    TOSAQuantizer,
-    VgfQuantizer,
-)
 
 # Used in tests
 from .arm_quantizer_utils import is_annotated  # noqa
 
+# Lazily import heavy quantizer classes to avoid circular imports with
+# Cortex-M quantization configs.
+_LAZY_EXPORTS = {
+    "EthosUQuantizer": "executorch.backends.arm.quantizer.arm_quantizer",
+    "get_symmetric_a16w8_quantization_config": "executorch.backends.arm.quantizer.arm_quantizer",
+    "get_symmetric_quantization_config": "executorch.backends.arm.quantizer.arm_quantizer",
+    "TOSAQuantizer": "executorch.backends.arm.quantizer.arm_quantizer",
+    "VgfQuantizer": "executorch.backends.arm.quantizer.arm_quantizer",
+}
+
+
+def __getattr__(name: str):
+    if name not in _LAZY_EXPORTS:
+        raise AttributeError(f"module {__name__!r} has no attribute {name!r}")
+    import importlib
+
+    module = importlib.import_module(_LAZY_EXPORTS[name])
+    return getattr(module, name)
+
+
+def __dir__():
+    return sorted(list(globals().keys()) + list(_LAZY_EXPORTS.keys()))
+
+
 # Load quantized ops library.
 try:
     import executorch.extension.pybindings.portable_lib