soc/mediatek/adsp: Build zephyr.ri using rimage when available

This is mostly a cut/paste copy of similar code in intel_adsp and imx,
which sadly can't be shared given the way the design works.  Also
includes a bonus, slightly-passive-aggressive description of why that
is.

Signed-off-by: Andy Ross <[email protected]>

Author: andyross

soc/mediatek/mt8xxx/CMakeLists.txt

@@ -12,3 +12,33 @@ add_custom_target(dsp_img ALL
 	COMMAND ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/gen_img.py
 		${ZEPHYR_BINARY_DIR}/${KERNEL_ELF_NAME}
 		${CMAKE_BINARY_DIR}/zephyr/zephyr.img)
+
+# Sign zephyr.ri using west (if the underlying rimage tool is
+# available; generally it isn't except in SOF builds).  Note that the
+# "target" string to use for rimage is set at the board level as a
+# RIMAGE_TARGET cached (cached so that the python script can read it!)
+# cmake variable (not kconfig!).  See board_set_rimage_target().
+# Thankfully the SOC name and the rimage target names for these
+# platforms are identical.  The west sign integration similarly needs
+# a RIMAGE_CONFIG_PATH cmake cached (!) variable set to a directory
+# containing the .toml files for the platforms, which SOF will set on
+# its own at build time.  And likewise the signing key isn't provided
+# by Zephyr and needs tob e found by a SOF build by passing it in
+# RIMAGE_SIGN_KEY.
+#
+# The short version is that zephyr.ri can only realistically be
+# exercised from a SOF build and it doesn't belong here in Zephyr;
+# rimage is a SOF tool.  Signing audio firmware is only done for SOF
+# firmware and not general Zephyr apps for the same hardware. This
+# should live in SOF where it doesn't have to be duplicated for every
+# device and where it won't be forced to communicate via side channels.
+board_set_rimage_target(${CONFIG_SOC})
+set(RIMAGE_SIGN_KEY "otc_private_key_3k.pem" CACHE STRING "default rimage key")
+add_custom_target(zephyr.ri ALL DEPENDS ${CMAKE_BINARY_DIR}/zephyr/zephyr.ri)
+add_custom_command(
+	OUTPUT ${CMAKE_BINARY_DIR}/zephyr/zephyr.ri
+	COMMENT "Sign with rimage..."
+	COMMAND west $<$<BOOL:${CMAKE_VERBOSE_MAKEFILE}>:--verbose> sign
+                     --if-tool-available --tool rimage --build-dir ${CMAKE_BINARY_DIR}
+	DEPENDS ${CMAKE_BINARY_DIR}/zephyr/${KERNEL_ELF_NAME}
+)