1 .. SPDX-License-Identifier: GPL-2.0+
2 .. Copyright (c) 2017 Simon Glass <sjg@chromium.org>
10 U-Boot's internal operation involves many different steps and actions. From
11 setting up the board to displaying a start-up screen to loading an Operating
12 System, there are many component parts each with many actions.
14 Most of the time this internal detail is not useful. Displaying it on the
15 console would delay booting (U-Boot's primary purpose) and confuse users.
17 But for digging into what is happening in a particular area, or for debugging
18 a problem it is often useful to see what U-Boot is doing in more detail than
19 is visible from the basic console output.
21 U-Boot's logging feature aims to satisfy this goal for both users and
28 There are a number logging levels available, in increasing order of verbosity:
30 * LOGL_EMERG - Printed before U-Boot halts
31 * LOGL_ALERT - Indicates action must be taken immediate or U-Boot will crash
32 * LOGL_CRIT - Indicates a critical error that will cause boot failure
33 * LOGL_ERR - Indicates an error that may cause boot failure
34 * LOGL_WARNING - Warning about an unexpected condition
35 * LOGL_NOTE - Important information about progress
36 * LOGL_INFO - Information about normal boot progress
37 * LOGL_DEBUG - Debug information (useful for debugging a driver or subsystem)
38 * LOGL_DEBUG_CONTENT - Debug message showing full message content
39 * LOGL_DEBUG_IO - Debug message showing hardware I/O access
45 Logging can come from a wide variety of places within U-Boot. Each log message
46 has a category which is intended to allow messages to be filtered according to
49 The following main categories are defined:
51 * LOGC_NONE - Unknown category (e.g. a debug() statement)
52 * UCLASS\_... - Related to a particular uclass (e.g. UCLASS_USB)
53 * LOGC_ARCH - Related to architecture-specific code
54 * LOGC_BOARD - Related to board-specific code
55 * LOGC_CORE - Related to core driver-model support
56 * LOGC_DT - Related to device tree control
57 * LOGC_EFI - Related to EFI implementation
63 The following options are used to enable logging at compile time:
65 * CONFIG_LOG - Enables the logging system
66 * CONFIG_LOG_MAX_LEVEL - Max log level to build (anything higher is compiled
68 * CONFIG_LOG_CONSOLE - Enable writing log records to the console
70 If CONFIG_LOG is not set, then no logging will be available.
72 The above have SPL and TPL versions also, e.g. CONFIG_SPL_LOG_MAX_LEVEL and
73 CONFIG_TPL_LOG_MAX_LEVEL.
76 Temporary logging within a single file
77 --------------------------------------
79 Sometimes it is useful to turn on logging just in one file. You can use this
85 to enable building in of all logging statements in a single file. Put it at
86 the top of the file, before any #includes.
88 To actually get U-Boot to output this you need to also set the default logging
89 level - e.g. set CONFIG_LOG_DEFAULT_LEVEL to 7 (LOGL_DEBUG) or more. Otherwise
90 debug output is suppressed and will not be generated.
96 A number of convenience functions are available to shorten the code needed
100 * log_warning(_fmt...)
101 * log_notice(_fmt...)
104 * log_content(_fmt...)
107 With these the log level is implicit in the name. The category is set by
108 LOG_CATEGORY, which you can only define once per file, above all #includes, e.g.
112 #define LOG_CATEGORY LOGC_ALLOC
114 Remember that all uclasses IDs are log categories too.
120 The 'log' command provides access to several features:
122 * level - access the default log level
123 * format - access the console log format
124 * rec - output a log record
127 Type 'help log' for details.
133 U-Boot has traditionally used a #define called DEBUG to enable debugging on a
134 file-by-file basis. The debug() macro compiles to a printf() statement if
135 DEBUG is enabled, and an empty statement if not.
137 With logging enabled, debug() statements are interpreted as logging output
138 with a level of LOGL_DEBUG and a category of LOGC_NONE.
140 The logging facilities are intended to replace DEBUG, but if DEBUG is defined
141 at the top of a file, then it takes precedence. This means that debug()
142 statements will result in output to the console and this output will not be
149 If logging information goes nowhere then it serves no purpose. U-Boot provides
150 several possible determinations for logging information, all of which can be
151 enabled or disabled independently:
153 * console - goes to stdout
154 * syslog - broadcast RFC 3164 messages to syslog servers on UDP port 514
156 The syslog driver sends the value of environmental variable 'log_hostname' as
157 HOSTNAME if available.
163 You can control the log format using the 'log format' command. The basic
166 LEVEL.category,file.c:123-func() message
168 In the above, file.c:123 is the filename where the log record was generated and
169 func() is the function name. By default ('log format default') only the
170 function name and message are displayed on the console. You can control which
171 fields are present, but not the field order.
177 Filters are attached to log drivers to control what those drivers emit. Only
178 records that pass through the filter make it to the driver.
180 Filters can be based on several criteria:
183 * in a set of categories
186 If no filters are attached to a driver then a default filter is used, which
187 limits output to records with a level less than CONFIG_MAX_LOG_LEVEL.
193 The main logging function is:
197 log(category, level, format_string, ...)
199 Also debug() and error() will generate log records - these use LOG_CATEGORY
200 as the category, so you should #define this right at the top of the source
201 file to ensure the category is correct.
203 You can also define CONFIG_LOG_ERROR_RETURN to enable the log_ret() macro. This
204 can be used whenever your function returns an error value:
208 return log_ret(uclass_first_device(UCLASS_MMC, &dev));
210 This will write a log record when an error code is detected (a value < 0). This
211 can make it easier to trace errors that are generated deep in the call stack.
217 Code size impact depends largely on what is enabled. The following numbers are
218 generated by 'buildman -S' for snow, which is a Thumb-2 board (all units in
221 This series: adds bss +20.0 data +4.0 rodata +4.0 text +44.0
222 CONFIG_LOG: bss -52.0 data +92.0 rodata -635.0 text +1048.0
223 CONFIG_LOG_MAX_LEVEL=7: bss +188.0 data +4.0 rodata +49183.0 text +98124.0
225 The last option turns every debug() statement into a logging call, which
226 bloats the code hugely. The advantage is that it is then possible to enable
227 all logging within U-Boot.
233 There are lots of useful additions that could be made. None of the below is
234 implemented! If you do one, please add a test in test/py/tests/test_log.py
236 Convenience functions to support setting the category:
238 * log_arch(level, format_string, ...) - category LOGC_ARCH
239 * log_board(level, format_string, ...) - category LOGC_BOARD
240 * log_core(level, format_string, ...) - category LOGC_CORE
241 * log_dt(level, format_string, ...) - category LOGC_DT
243 More logging destinations:
245 * device - goes to a device (e.g. serial)
246 * buffer - recorded in a memory buffer
248 Convert debug() statements in the code to log() statements
250 Support making printf() emit log statements at L_INFO level
252 Convert error() statements in the code to log() statements
254 Figure out what to do with BUG(), BUG_ON() and warn_non_spl()
256 Figure out what to do with assert()
258 Add a way to browse log records
260 Add a way to record log records for browsing using an external tool
262 Add commands to add and remove filters
264 Add commands to add and remove log devices
266 Allow sharing of printf format strings in log records to reduce storage size
267 for large numbers of log records
269 Add a command-line option to sandbox to set the default logging level
271 Convert core driver model code to use logging
273 Convert uclasses to use logging with the correct category
275 Consider making log() calls emit an automatic newline, perhaps with a logn()
276 function to avoid that
278 Passing log records through to linux (e.g. via device tree /chosen)
280 Provide a command to access the number of log records generated, and the
281 number dropped due to them being generated before the log system was ready.
283 Add a printf() format string pragma so that log statements are checked properly
285 Enhance the log console driver to show level / category / file / line
288 Add a command to add new log records and delete existing records.
290 Provide additional log() functions - e.g. logc() to specify the category