Arm backend: Add docstrings for tosa/dialect/lib.py (pytorch#15828)

cc @freddan80 @per @zingo @oscarandersson8218 @digantdesai

Signed-off-by: Sebastian Larsson <[email protected]>
Co-authored-by: Zingo Andersen <[email protected]>

Author: Sebastian-Larsson

backends/arm/tosa/dialect/lib.py

@@ -15,6 +15,17 @@
 
 
 def register_tosa_dialect_op(op_schema, func) -> Callable:
+    """Register a TOSA dialect operator with the backend op library.
+
+    Args:
+        op_schema (str): Operator schema without namespace or overload name.
+        func (Callable): Fake implementation used for registration.
+
+    Returns:
+        Callable: Backend dialect operator handle exposed via ``exir_ops`` and
+        marked ``not_callable`` for runtime use.
+
+    """
     if tosa_lib.ns not in _BACKEND_OP_LIB:
         _BACKEND_OP_LIB.append(tosa_lib.ns)
 
@@ -43,6 +54,7 @@ def register_tosa_dialect_op(op_schema, func) -> Callable:
     # the op doesn't need to be callable. This can be changed in the future if needed to support
     # execution of TOSA ops directly.
     def not_callable():
+        """Raise when the dialect op handle is invoked at runtime."""
         raise RuntimeError("TOSA dialect op is not callable")
 
     op.__equvalent_callable__ = not_callable
@@ -51,11 +63,22 @@ def not_callable():
 
 
 class TosaValueError(ValueError):
+    """Error type that annotates failures with the originating TOSA op."""
+
     def __init__(self, message="A TOSA value error occurred", *args, op=None):
+        """Initialise the error with optional operator metadata.
+
+        Args:
+            message (str): Human-readable error message.
+            *args: Additional arguments forwarded to ``ValueError``.
+            op: Optional operator identifier included in the string output.
+
+        """
         super().__init__(message, *args)
         self.op = op
 
     def __str__(self):
+        """Return the base message, appending the operator when provided."""
         base_message = super().__str__()
         if self.op is not None:
             return f"{base_message} (TOSA op: {self.op})"