7 U-Boot's internal operation involves many different steps and actions. From
8 setting up the board to displaying a start-up screen to loading an Operating
9 System, there are many component parts each with many actions.
11 Most of the time this internal detail is not useful. Displaying it on the
12 console would delay booting (U-Boot's primary purpose) and confuse users.
14 But for digging into what is happening in a particular area, or for debugging
15 a problem it is often useful to see what U-Boot is doing in more detail than
16 is visible from the basic console output.
18 U-Boot's logging feature aims to satisfy this goal for both users and
25 There are a number logging levels available, in increasing order of verbosity:
27 LOGL_EMERG - Printed before U-Boot halts
28 LOGL_ALERT - Indicates action must be taken immediate or U-Boot will crash
29 LOGL_CRIT - Indicates a critical error that will cause boot failure
30 LOGL_ERR - Indicates an error that may cause boot failure
31 LOGL_WARNING - Warning about an unexpected condition
32 LOGL_NOTE - Important information about progress
33 LOGL_INFO - Information about normal boot progress
34 LOGL_DEBUG - Debug information (useful for debugging a driver or subsystem)
35 LOGL_DEBUG_CONTENT - Debug message showing full message content
36 LOGL_DEBUG_IO - Debug message showing hardware I/O access
42 Logging can come from a wide variety of places within U-Boot. Each log message
43 has a category which is intended to allow messages to be filtered according to
46 The following main categories are defined:
48 LOGC_NONE - Unknown category (e.g. a debug() statement)
49 UCLASS_... - Related to a particular uclass (e.g. UCLASS_USB)
50 LOGC_ARCH - Related to architecture-specific code
51 LOGC_BOARD - Related to board-specific code
52 LOGC_CORE - Related to core driver-model support
53 LOGC_DT - Related to device tree control
54 LOGC_EFI - Related to EFI implementation
60 The following options are used to enable logging at compile time:
62 CONFIG_LOG - Enables the logging system
63 CONFIG_MAX_LOG_LEVEL - Max log level to build (anything higher is compiled
65 CONFIG_LOG_CONSOLE - Enable writing log records to the console
67 If CONFIG_LOG is not set, then no logging will be available.
69 The above have SPL versions also, e.g. CONFIG_SPL_MAX_LOG_LEVEL.
72 Temporary logging within a single file
73 --------------------------------------
75 Sometimes it is useful to turn on logging just in one file. You can use this:
79 to enable building in of all logging statements in a single file. Put it at
80 the top of the file, before any #includes.
82 To actually get U-Boot to output this you need to also set the default logging
83 level - e.g. set CONFIG_LOG_DEFAULT_LEVEL to 7 (LOGL_DEBUG) or more. Otherwise
84 debug output is suppressed and will not be generated.
90 A number of convenience functions are available to shorten the code needed
101 With these the log level is implicit in the name. The category is set by
102 LOG_CATEGORY, which you can only define once per file, above all #includes:
104 #define LOG_CATEGORY LOGC_ALLOC
108 #define LOG_CATEGORY UCLASS_SPI
110 Remember that all uclasses IDs are log categories too.
116 The 'log' command provides access to several features:
118 level - access the default log level
119 format - access the console log format
120 rec - output a log record
123 Type 'help log' for details.
129 U-Boot has traditionally used a #define called DEBUG to enable debugging on a
130 file-by-file basis. The debug() macro compiles to a printf() statement if
131 DEBUG is enabled, and an empty statement if not.
133 With logging enabled, debug() statements are interpreted as logging output
134 with a level of LOGL_DEBUG and a category of LOGC_NONE.
136 The logging facilities are intended to replace DEBUG, but if DEBUG is defined
137 at the top of a file, then it takes precedence. This means that debug()
138 statements will result in output to the console and this output will not be
145 If logging information goes nowhere then it serves no purpose. U-Boot provides
146 several possible determinations for logging information, all of which can be
147 enabled or disabled independently:
149 console - goes to stdout
150 syslog - broadcast RFC 3164 messages to syslog servers on UDP port 514
152 The syslog driver sends the value of environmental variable 'log_hostname' as
153 HOSTNAME if available.
158 You can control the log format using the 'log format' command. The basic
161 LEVEL.category,file.c:123-func() message
163 In the above, file.c:123 is the filename where the log record was generated and
164 func() is the function name. By default ('log format default') only the
165 function name and message are displayed on the console. You can control which
166 fields are present, but not the field order.
172 Filters are attached to log drivers to control what those drivers emit. Only
173 records that pass through the filter make it to the driver.
175 Filters can be based on several criteria:
178 - in a set of categories
181 If no filters are attached to a driver then a default filter is used, which
182 limits output to records with a level less than CONFIG_LOG_MAX_LEVEL.
188 The main logging function is:
190 log(category, level, format_string, ...)
192 Also debug() and error() will generate log records - these use LOG_CATEGORY
193 as the category, so you should #define this right at the top of the source
194 file to ensure the category is correct.
196 You can also define CONFIG_LOG_ERROR_RETURN to enable the log_ret() macro. This
197 can be used whenever your function returns an error value:
199 return log_ret(uclass_first_device(UCLASS_MMC, &dev));
201 This will write a log record when an error code is detected (a value < 0). This
202 can make it easier to trace errors that are generated deep in the call stack.
208 Code size impact depends largely on what is enabled. The following numbers are
209 generated by 'buildman -S' for snow, which is a Thumb-2 board (all units in
212 This series: adds bss +20.0 data +4.0 rodata +4.0 text +44.0
213 CONFIG_LOG: bss -52.0 data +92.0 rodata -635.0 text +1048.0
214 CONFIG_LOG_MAX_LEVEL=7: bss +188.0 data +4.0 rodata +49183.0 text +98124.0
216 The last option turns every debug() statement into a logging call, which
217 bloats the code hugely. The advantage is that it is then possible to enable
218 all logging within U-Boot.
224 There are lots of useful additions that could be made. None of the below is
225 implemented! If you do one, please add a test in test/py/tests/test_log.py
227 Convenience functions to support setting the category:
229 log_arch(level, format_string, ...) - category LOGC_ARCH
230 log_board(level, format_string, ...) - category LOGC_BOARD
231 log_core(level, format_string, ...) - category LOGC_CORE
232 log_dt(level, format_string, ...) - category LOGC_DT
234 More logging destinations:
236 device - goes to a device (e.g. serial)
237 buffer - recorded in a memory buffer
239 Convert debug() statements in the code to log() statements
241 Support making printf() emit log statements a L_INFO level
243 Convert error() statements in the code to log() statements
245 Figure out what to do with BUG(), BUG_ON() and warn_non_spl()
247 Figure out what to do with assert()
249 Add a way to browse log records
251 Add a way to record log records for browsing using an external tool
253 Add commands to add and remove filters
255 Add commands to add and remove log devices
257 Allow sharing of printf format strings in log records to reduce storage size
258 for large numbers of log records
260 Add a command-line option to sandbox to set the default logging level
262 Convert core driver model code to use logging
264 Convert uclasses to use logging with the correct category
266 Consider making log() calls emit an automatic newline, perhaps with a logn()
267 function to avoid that
269 Passing log records through to linux (e.g. via device tree /chosen)
271 Provide a command to access the number of log records generated, and the
272 number dropped due to them being generated before the log system was ready.
274 Add a printf() format string pragma so that log statements are checked properly
276 Enhance the log console driver to show level / category / file / line
279 Add a command to add new log records and delete existing records.
281 Provide additional log() functions - e.g. logc() to specify the category
284 Simon Glass <sjg@chromium.org>