Arm backend: Add docstrings to vgf/backend.py and ethosu/backend.py (#15887)

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/ethosu/backend.py

@@ -9,6 +9,7 @@
 # backends. Converts via TOSA as an intermediate form supported by AoT and
 # JIT compiler flows.
 #
+"""Ahead-of-time Arm Ethos-U backend built on the shared TOSA pipeline."""
 
 import logging
 from typing import final, List
@@ -27,19 +28,28 @@
 
 @final
 class EthosUBackend(BackendDetails):
-    """
-    BackendDetails subclass for delegation to Ethos-U. Deduce the TOSA lowering from
-    the compile spec list by filtering out the compile spec values that are of interest
-    for the TOSABackend.
+    """BackendDetails subclass for delegation to Ethos-U.
+
+    Deduce the TOSA lowering from the compile spec list by filtering out the
+    compile spec values that are of interest for the TOSABackend.
+
     """
 
     @staticmethod
     def _compile_tosa_flatbuffer(
         tosa_flatbuffer: bytes, compile_spec: EthosUCompileSpec
     ) -> bytes:
-        """
-        Static helper method to do the compilation of the TOSA flatbuffer
-        representation to a target specific binary stream.
+        """Compile a TOSA flatbuffer into a target-specific binary stream.
+
+        Args:
+            tosa_flatbuffer (bytes): Serialized TOSA graph produced by
+                ``TOSABackend``.
+            compile_spec (EthosUCompileSpec): Compile specification providing
+                Vela flags and intermediate paths.
+
+        Returns:
+            bytes: Target-specific binary stream produced by Vela.
+
         """
         compile_flags = compile_spec.compiler_flags
 
@@ -73,6 +83,17 @@ def preprocess(
         edge_program: ExportedProgram,
         compile_specs: List[CompileSpec],
     ) -> PreprocessResult:
+        """Lower the exported program and compile it for an Ethos-U target.
+
+        Args:
+            edge_program (ExportedProgram): Program to lower to Ethos-U.
+            compile_specs (List[CompileSpec]): Serialized Ethos-U compile specs
+                supplied by the frontend.
+
+        Returns:
+            PreprocessResult: Result containing the compiled Ethos-U binary.
+
+        """
         logger.info(f"{EthosUBackend.__name__} preprocess")
 
         compile_spec = EthosUCompileSpec.from_list(compile_specs)

backends/arm/vgf/backend.py

@@ -10,6 +10,7 @@
 # this form is used where the final JIT compile is performed on target (in the
 # runtime delegate executorch::runtime::BackendInterface::init
 #
+"""Ahead-of-time Arm VGF backend built on the shared TOSA pipeline."""
 
 import logging
 import os
@@ -43,9 +44,11 @@
 
 @final
 class VgfBackend(BackendDetails):
-    """
-    BackendDetails subclass for delegation to VGF compatible devices. This enables
-    encapsulated TOSA on target device and JIT compilation on suitable platforms.
+    """BackendDetails subclass for delegation to VGF compatible devices.
+
+    This enables encapsulated TOSA on target device and JIT compilation on
+    suitable platforms.
+
     """
 
     @staticmethod
@@ -54,9 +57,18 @@ def _compile_tosa_flatbuffer(
         compile_spec: VgfCompileSpec,
         tag_name: str = "",
     ) -> bytes:
-        """
-        Static helper method to do the compilation of the TOSA flatbuffer
-        representation to a target specific binary stream.
+        """Compile a TOSA flatbuffer into a target-specific binary stream.
+
+        Args:
+            tosa_flatbuffer (bytes): Serialized TOSA graph produced by
+                ``TOSABackend``.
+            compile_spec (VgfCompileSpec): Compile specification providing
+                converter flags and artifact paths.
+            tag_name (str): Optional suffix used when producing debug outputs.
+
+        Returns:
+            bytes: Target-specific VGF binary stream.
+
         """
         compile_flags = compile_spec.compiler_flags
         artifact_path = compile_spec.get_intermediate_path()
@@ -69,6 +81,17 @@ def preprocess(
         edge_program: ExportedProgram,
         compile_specs: List[CompileSpec],
     ) -> PreprocessResult:
+        """Lower the exported program and compile it for a VGF target.
+
+        Args:
+            edge_program (ExportedProgram): Program to lower to VGF.
+            compile_specs (List[CompileSpec]): Serialized VGF compile specs
+                supplied by the frontend.
+
+        Returns:
+            PreprocessResult: Result containing the compiled VGF binary.
+
+        """
         logger.info(f"{VgfBackend.__name__} preprocess")
 
         compile_spec = VgfCompileSpec.from_list(compile_specs)
@@ -98,6 +121,20 @@ def vgf_compile(
     artifact_path: str | None = None,
     tag_name: str = "",
 ):
+    """Invoke the VGF compiler to convert a TOSA flatbuffer.
+
+    Args:
+        tosa_flatbuffer (bytes): Serialized TOSA graph produced by
+            ``TOSABackend``.
+        compile_flags (List[str]): Command-line flags forwarded to
+            ``model-converter``.
+        artifact_path (str | None): Directory where debug artifacts are saved.
+        tag_name (str): Optional suffix used when producing debug outputs.
+
+    Returns:
+        bytes: Compiled VGF binary emitted by ``model-converter``.
+
+    """
     with tempfile.TemporaryDirectory() as tmpdir:
 
         # We currently write out a flatbuffer as input to the converter