zdsp: Fix missing kconfig and no source library

Adds a missing menuconfig for the DSP library as well as fix an issue
with the zephyr library being a STATIC library and having no sources
in the case of the cmsis backend.

Signed-off-by: Yuval Peress <peress@google.com>

subsys/CMakeLists.txt

@@ -19,7 +19,7 @@ add_subdirectory(random)
 add_subdirectory(storage)
 add_subdirectory_ifdef(CONFIG_SETTINGS             settings)
 add_subdirectory(fb)
-add_subdirectory(dsp)
+add_subdirectory_ifdef(CONFIG_DSP                  dsp)
 add_subdirectory(portability)
 add_subdirectory(pm)
 add_subdirectory(stats)

subsys/dsp/CMakeLists.txt

@@ -1,8 +1,4 @@
 # Copyright (c) 2022 Google LLC
 # SPDX-License-Identifier: Apache-2.0
 
-zephyr_library_named(zdsp)
-
 add_subdirectory_ifdef(CONFIG_DSP_BACKEND_CMSIS cmsis)
-
-zephyr_link_libraries(zdsp)

subsys/dsp/Kconfig

@@ -1,6 +1,15 @@
 # Copyright (c) 2022 Google LLC
 # SPDX-License-Identifier: Apache-2.0
 
+menuconfig DSP
+	bool "DSP subsystem"
+	help
+	  Include the DSP (Digital Signal Processing) subsystem as a part of the
+	  Zephyr build. This enables applications to include and call into the
+	  <zephyr/dsp/dsp.h> header.
+
+if DSP
+
 config DSP_BACKEND_HAS_STATIC
 	bool
 
@@ -24,3 +33,5 @@ config DSP_BACKEND_CUSTOM
 	  added to the 'zdsp' build target by the application or one of its modules.
 
 endchoice
+
+endif # DSP

subsys/dsp/cmsis/CMakeLists.txt

@@ -1,4 +1,4 @@
 # Copyright (c) 2022 Google LLC
 # SPDX-License-Identifier: Apache-2.0
 
-target_include_directories(zdsp PUBLIC public)
+zephyr_include_directories(public)

tests/subsys/dsp/basicmath/prj.conf

@@ -1,6 +1,7 @@
 CONFIG_ZTEST=y
 CONFIG_ZTEST_NEW_API=y
 CONFIG_NEWLIB_LIBC=y
+CONFIG_DSP=y
 CONFIG_CMSIS_DSP=y
 CONFIG_CMSIS_DSP_BASICMATH=y
 CONFIG_DSP_BACKEND_CMSIS=y