Makefile updates for Arm(R) CPU targets (#3064)

Removing redundant assignments for CMSIS_PATH and adding the possibility to override Device Family Pack (DFP) path with a new CORTEX_DFP_PATH make variable.

This allows flexibility in where the CMSIS and DFP sources reside.

BUG=More flexible build structure

Author: AdrianLundell

tensorflow/lite/micro/kernels/cmsis_nn/README.md

@@ -16,6 +16,11 @@ CMSIS_PATH=<../path> and CMSIS_NN_PATH=<../path>. Note that both CMSIS_PATH and
 since CMSIS-NN has a dependency to CMSIS-Core. As a third option CMSIS-NN can be provided manually as an external library.
 The examples below will illustrate this.
 
+# Specifying path to Cortex_DFP
+
+The Cortex_DFP path used can be specified using an additional flag `CORTEX_DFP_PATH=<path/to>cmsis/Cortex_DFP`.
+Default is the Cortex_DFP contained in the downloaded CMSIS version.
+
 ## Example - FVP based on Arm Corstone-300 software.
 In this example, the kernel conv unit test is built. For more information about
 this specific target, check out the [Corstone-300 readme](https://github.com/tensorflow/tflite-micro/tree/main/tensorflow/lite/micro/cortex_m_corstone_300/README.md).

tensorflow/lite/micro/tools/make/targets/cortex_m_corstone_300_makefile.inc

@@ -1,4 +1,4 @@
-# Copyright 2024 The TensorFlow Authors. All Rights Reserved.
+# Copyright 2025 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -37,6 +37,7 @@ endif
 # This target has dependencies to CMSIS-Device so just in case running without OPTIMIZED_KERNEL_DIR=cmsis_nn.
 CMSIS_DEFAULT_DOWNLOAD_PATH := $(DOWNLOADS_DIR)/cmsis
 CMSIS_PATH := $(CMSIS_DEFAULT_DOWNLOAD_PATH)
+CORTEX_DFP_PATH := $(CMSIS_PATH)/Cortex_DFP
 ifeq ($(CMSIS_PATH), $(CMSIS_DEFAULT_DOWNLOAD_PATH))
   DOWNLOAD_RESULT := $(shell $(MAKEFILE_DIR)/ext_libs/cmsis_download.sh $(DOWNLOADS_DIR) $(TENSORFLOW_ROOT))
   ifneq ($(DOWNLOAD_RESULT), SUCCESS)
@@ -194,13 +195,11 @@ ifeq ($(CO_PROCESSOR), ethos_u)
   ETHOSU_ARCH=u55
 endif
 
-CMSIS_DEFAULT_DOWNLOAD_PATH := $(DOWNLOADS_DIR)/cmsis
-CMSIS_PATH := $(CMSIS_DEFAULT_DOWNLOAD_PATH)
 THIRD_PARTY_CC_SRCS += \
-  $(CMSIS_PATH)/Cortex_DFP/Device/$(ARM_CPU)/Source/system_$(ARM_CPU).c \
-  $(CMSIS_PATH)/Cortex_DFP/Device/$(ARM_CPU)/Source/startup_$(ARM_CPU).c
+  $(CORTEX_DFP_PATH)/Device/$(ARM_CPU)/Source/system_$(ARM_CPU).c \
+  $(CORTEX_DFP_PATH)/Device/$(ARM_CPU)/Source/startup_$(ARM_CPU).c
 INCLUDES += \
-  -I$(CMSIS_PATH)/Cortex_DFP/Device/$(ARM_CPU)/Include \
+  -I$(CORTEX_DFP_PATH)/Device/$(ARM_CPU)/Include \
   -I$(CMSIS_PATH)/CMSIS/Core/Include
 
 # TODO(#274): Examine why some tests fail here.

tensorflow/lite/micro/tools/make/targets/cortex_m_generic_makefile.inc

@@ -1,4 +1,4 @@
-# Copyright 2024 The TensorFlow Authors. All Rights Reserved.
+# Copyright 2025 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@
 # Needed in case running without OPTIMIZED_KERNEL_DIR=cmsis_nn.
 CMSIS_DEFAULT_DOWNLOAD_PATH := $(DOWNLOADS_DIR)/cmsis
 CMSIS_PATH := $(CMSIS_DEFAULT_DOWNLOAD_PATH)
+CORTEX_DFP_PATH := $(CMSIS_PATH)/Cortex_DFP
 ifeq ($(CMSIS_PATH), $(CMSIS_DEFAULT_DOWNLOAD_PATH))
   DOWNLOAD_RESULT := $(shell $(MAKEFILE_DIR)/ext_libs/cmsis_download.sh $(DOWNLOADS_DIR) $(TENSORFLOW_ROOT))
   ifneq ($(DOWNLOAD_RESULT), SUCCESS)
@@ -108,10 +109,8 @@ endif
 
 # Dependency to CMSIS-Device for DWT/PMU counters.
 ARM_CPU := "ARMC$(CORE)"
-CMSIS_DEFAULT_DOWNLOAD_PATH := $(MAKEFILE_DIR)/downloads/cmsis
-CMSIS_PATH := $(CMSIS_DEFAULT_DOWNLOAD_PATH)
 INCLUDES += \
-  -I$(CMSIS_PATH)/Cortex_DFP/Device/$(ARM_CPU)/Include \
+  -I$(CORTEX_DFP_PATH)/Device/$(ARM_CPU)/Include \
   -I$(CMSIS_PATH)/CMSIS/Core/Include
 
 ifneq ($(filter cortex-m55%,$(TARGET_ARCH)),)