logging: Allow for compilation without log_output

Add option to Kconfig to enable log_output module. It is used
by most of the backends but it is an optional formatter helper
thus it is possible to run logging without it. One example might
be dictionary based logging which does not format log message
to a readable string.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>

subsys/logging/CMakeLists.txt

@@ -9,6 +9,11 @@ if(NOT CONFIG_LOG_MODE_MINIMAL)
     log_output.c
   )
 
+  zephyr_sources_ifdef(
+    CONFIG_LOG_OUTPUT
+    log_output.c
+  )
+
   # Determine if __auto_type is supported. If not then runtime approach must always
   # be used.
   # Supported by:

subsys/logging/Kconfig

@@ -16,13 +16,17 @@ rsource "Kconfig.filtering"
 
 rsource "Kconfig.processing"
 
-if !LOG_FRONTEND_ONLY && !LOG_MODE_MINIMAL
+if !LOG_MODE_MINIMAL
 
 rsource "Kconfig.formatting"
 
+if !LOG_FRONTEND_ONLY
+
 rsource "Kconfig.backends"
 
-endif # !LOG_FRONTEND_ONLY && !LOG_MODE_MINIMAL
+endif # !LOG_FRONTEND_ONLY
+
+endif # !LOG_MODE_MINIMAL
 
 if LOG_FRONTEND
 

subsys/logging/Kconfig.backends

@@ -7,6 +7,7 @@ config LOG_BACKEND_UART
 	bool "UART backend"
 	depends on UART_CONSOLE
 	default y if !SHELL_BACKEND_SERIAL
+	select LOG_OUTPUT
 	help
 	  When enabled backend is using UART to output logs.
 
@@ -54,6 +55,7 @@ endif # LOG_BACKEND_UART
 config LOG_BACKEND_SWO
 	bool "Serial Wire Output (SWO) backend"
 	depends on HAS_SWO
+	select LOG_OUTPUT
 	help
 	  When enabled, backend will use SWO for logging.
 
@@ -85,6 +87,7 @@ config LOG_BACKEND_RTT
 	depends on USE_SEGGER_RTT
 	default y if !SHELL_BACKEND_RTT
 	select SEGGER_RTT_CUSTOM_LOCKING
+	select LOG_OUTPUT
 	help
 	  When enabled, backend will use RTT for logging. This backend works on a per
 	  message basis. Only a whole message (terminated with a carriage return: '\r')
@@ -189,6 +192,7 @@ config LOG_BACKEND_SPINEL
 	bool "OpenThread dedicated Spinel protocol backend"
 	depends on !LOG_BACKEND_UART
 	depends on NET_L2_OPENTHREAD
+	select LOG_OUTPUT
 	help
 	  When enabled, backend will use OpenThread dedicated SPINEL protocol for logging.
 	  This protocol is byte oriented and wraps given messages into serial frames.
@@ -213,6 +217,7 @@ config LOG_BACKEND_NATIVE_POSIX
 	bool "Native backend"
 	depends on ARCH_POSIX
 	default y if !SERIAL
+	select LOG_OUTPUT
 	help
 	  Enable backend in native_posix
 
@@ -228,6 +233,7 @@ config LOG_BACKEND_XTENSA_SIM
 	bool "Xtensa simulator backend"
 	depends on SOC_XTENSA_SAMPLE_CONTROLLER || SOC_FAMILY_INTEL_ADSP
 	default y if SOC_XTENSA_SAMPLE_CONTROLLER
+	select LOG_OUTPUT
 	help
 	  Enable backend in xtensa simulator
 
@@ -253,6 +259,7 @@ config LOG_BACKEND_NET
 	bool "Networking backend"
 	depends on NETWORKING && NET_UDP && !LOG_MODE_IMMEDIATE
 	select NET_CONTEXT_NET_PKT_POOL
+	select LOG_OUTPUT
 	help
 	  Send syslog messages to network server.
 	  See RFC 5424 (syslog protocol) and RFC 5426 (syslog over UDP)
@@ -313,6 +320,7 @@ endif # LOG_BACKEND_NET
 config LOG_BACKEND_ADSP
 	bool "Intel ADSP buffer backend"
 	depends on SOC_FAMILY_INTEL_ADSP
+	select LOG_OUTPUT
 	help
 	  Enable backend for the host trace protocol of the Intel ADSP
 	  family of audio processors
@@ -328,6 +336,7 @@ endif # LOG_BACKEND_ADSP
 config LOG_BACKEND_CAVS_HDA
 	bool "cAVS HDA backend"
 	depends on SOC_FAMILY_INTEL_ADSP && DMA && DMA_CAVS_HDA
+	select LOG_OUTPUT
 	help
 	  Provide a logging backend which writes to a buffer and
 	  periodically flushes to hardware using ringbuffer like
@@ -363,6 +372,7 @@ endif # LOG_BACKEND_CAVS_HDA
 config LOG_BACKEND_FS
 	bool "File system backend"
 	depends on FILE_SYSTEM
+	select LOG_OUTPUT
 	help
 	  When enabled, backend is using the configured file system to output logs.
 	  As the file system must be mounted for the logging to work, it must be

subsys/logging/Kconfig.formatting

@@ -21,6 +21,12 @@ config LOG_FUNC_NAME_PREFIX_DBG
 
 endmenu
 
+config LOG_OUTPUT
+	bool "Formatter helper"
+	help
+	  Module which provides formatting of log messages to a human-readable
+	  strings.
+
 menuconfig LOG_MIPI_SYST_ENABLE
 	bool "MIPI SyS-T format output"
 	select MIPI_SYST_LIB

subsys/logging/log_core.c

@@ -54,7 +54,8 @@ BUILD_ASSERT(!IS_ENABLED(CONFIG_LOG_MODE_IMMEDIATE),
 #endif
 
 static const log_format_func_t format_table[] = {
-	[LOG_OUTPUT_TEXT] = log_output_msg_process,
+	[LOG_OUTPUT_TEXT] = IS_ENABLED(CONFIG_LOG_OUTPUT) ?
+						log_output_msg_process : NULL,
 	[LOG_OUTPUT_SYST] = IS_ENABLED(CONFIG_LOG_MIPI_SYST_ENABLE) ?
 						log_output_msg_syst_process : NULL,
 	[LOG_OUTPUT_DICT] = IS_ENABLED(CONFIG_LOG_DICTIONARY_SUPPORT) ?
@@ -330,7 +331,9 @@ int log_set_timestamp_func(log_timestamp_get_t timestamp_getter, uint32_t freq)
 	}
 
 	timestamp_func = timestamp_getter;
-	log_output_timestamp_freq_set(freq);
+	if (IS_ENABLED(CONFIG_LOG_OUTPUT)) {
+		log_output_timestamp_freq_set(freq);
+	}
 
 	return 0;
 }

tests/subsys/logging/log_output/prj.conf

@@ -2,4 +2,5 @@ CONFIG_MAIN_THREAD_PRIORITY=5
 CONFIG_ZTEST=y
 CONFIG_TEST_LOGGING_DEFAULTS=n
 CONFIG_LOG=y
+CONFIG_LOG_OUTPUT=y
 CONFIG_LOG_PRINTK=n

tests/subsys/logging/log_syst/prj.conf

@@ -2,6 +2,7 @@ CONFIG_LOG=y
 CONFIG_ASSERT=n
 CONFIG_ZTEST=y
 CONFIG_LOG_BACKEND_MOCK=y
+CONFIG_LOG_OUTPUT=y
 CONFIG_LOG_BACKEND_UART=n
 CONFIG_SOC_LOG_LEVEL_OFF=y
 CONFIG_ARCH_LOG_LEVEL_OFF=y