xtensa: don't build and run the reset handler twice

Currently Zephyr links reset-vector.S twice in xtensa builds:
into the bootloader and the main image. It is run at the end
of the boot loader execution and immediately after that again
in the beginning of the main code. This patch adds a
configuration option to select whether to link the file to the
bootloader or to the application. The default is to the
application, as needed e.g. for QEMU, SOF links it to the
bootloader like in native builds.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>

arch/xtensa/Kconfig

@@ -48,6 +48,15 @@ config XTENSA_RESET_VECTOR
 	  This is always needed for the simulator. Real boards may already
 	  implement this in boot ROM.
 
+if XTENSA_RESET_VECTOR
+config RESET_VECTOR_IN_BOOTLOADER
+	bool "Link reset vector into bootloader"
+	default n
+	help
+	  Reset vector code can be either linked in the bootloader or the
+	  application binary. Select "y" to link it into the bootloader.
+endif
+
 config XTENSA_USE_CORE_CRT1
 	bool "Use crt1.S from core"
 	default y

arch/xtensa/core/startup/CMakeLists.txt

@@ -9,8 +9,11 @@ if(CONFIG_XTENSA_RESET_VECTOR)
     -mlongcalls
     )
 
-  zephyr_library_sources(
+  zephyr_library_sources_ifndef(CONFIG_RESET_VECTOR_IN_BOOTLOADER
     reset-vector.S
+    )
+
+  zephyr_library_sources(
     memerror-vector.S
     memctl_default.S
     )

samples/audio/sof/prj.conf

@@ -3,6 +3,7 @@ CONFIG_SMP=n
 CONFIG_LOG=y
 CONFIG_MP_NUM_CPUS=1
 CONFIG_BUILD_OUTPUT_BIN=n
+CONFIG_RESET_VECTOR_IN_BOOTLOADER=y
 
 # Requires heap_info() be implemented, but no Zephyr wrapper
 CONFIG_DEBUG_MEMORY_USAGE_SCAN=n

soc/xtensa/intel_adsp/common/bootloader/CMakeLists.txt

@@ -26,11 +26,14 @@ add_executable(bootloader
   boot_entry.S
   ${ARCH_DIR}/${ARCH}/core/startup/memctl_default.S
   ${ARCH_DIR}/${ARCH}/core/startup/memerror-vector.S
-  ${ARCH_DIR}/${ARCH}/core/startup/reset-vector.S
   boot_loader.c
   start_address.S
   )
 
+target_sources_ifdef(CONFIG_RESET_VECTOR_IN_BOOTLOADER bootloader PRIVATE
+  ${ARCH_DIR}/${ARCH}/core/startup/reset-vector.S
+  )
+
 add_dependencies(bootloader ${SYSCALL_LIST_H_TARGET})
 
 set(zephyr_sdk $ENV{ZEPHYR_SDK_INSTALL_DIR})
@@ -69,7 +72,9 @@ add_custom_command(TARGET bootloader
  )
 
 set_source_files_properties(boot_entry.S PROPERTIES COMPILE_FLAGS -DASSEMBLY)
-set_source_files_properties(${ARCH_DIR}/${ARCH}/core/startup/reset-vector.S PROPERTIES COMPILE_FLAGS -DBOOTLOADER)
+if(CONFIG_RESET_VECTOR_IN_BOOTLOADER)
+  set_source_files_properties(${ARCH_DIR}/${ARCH}/core/startup/reset-vector.S PROPERTIES COMPILE_FLAGS -DBOOTLOADER)
+endif()
 
 target_compile_options(bootloader PUBLIC -fno-inline-functions -mlongcalls -mtext-section-literals -imacros${CMAKE_BINARY_DIR}/zephyr/include/generated/autoconf.h)
 

soc/xtensa/intel_adsp/common/bootloader/start_address.S

@@ -9,3 +9,16 @@
 	.global	_start
 	.equ    _start, SOF_TEXT_BASE
 
+#ifndef CONFIG_RESET_VECTOR_IN_BOOTLOADER
+	.begin	literal_prefix	.ResetVector
+	.section		.ResetVector.text, "ax"
+
+	.literal_position
+
+	.align	4
+	.global	__start
+
+__start:
+	movi	a0, 0
+	call0	_start		 /* jump to _start (in crt1-*.S) */
+#endif

soc/xtensa/intel_adsp/common/main_entry.S

@@ -27,7 +27,11 @@
 
 _MainEntry:
 
+#ifdef CONFIG_RESET_VECTOR_IN_BOOTLOADER
+	j	_start
+#else
 	j	__start
+#endif
 
 	.size	_MainEntry, . - _MainEntry