feat(docs): reorganize docs (#7136)

docs/details/debugging/log.rst

@@ -0,0 +1,71 @@
+.. _logging:
+
+=======
+Logging
+=======
+
+LVGL has a built-in *Log* module to inform the user about what is
+happening in the library.
+
+Log level
+*********
+
+To enable logging, set :c:macro:`LV_USE_LOG` in ``lv_conf.h`` and set
+:c:macro:`LV_LOG_LEVEL` to one of the following values:
+
+- :c:macro:`LV_LOG_LEVEL_TRACE`: A lot of logs to give detailed information
+- :c:macro:`LV_LOG_LEVEL_INFO`: Log important events
+- :c:macro:`LV_LOG_LEVEL_WARN`: Log if something unwanted happened but didn't cause a problem
+- :c:macro:`LV_LOG_LEVEL_ERROR`: Only critical issues, where the system may fail
+- :c:macro:`LV_LOG_LEVEL_USER`: Only user messages
+- :c:macro:`LV_LOG_LEVEL_NONE`: Do not log anything
+
+The events which have a higher level than the set log level will be logged
+as well. E.g. if you :c:macro:`LV_LOG_LEVEL_WARN`, errors will be also logged.
+
+
+Printing logs
+*************
+
+Logging with printf
+-------------------
+
+If your system supports ``printf``, you just need to enable
+:c:macro:`LV_LOG_PRINTF` in ``lv_conf.h`` to send the logs with ``printf``.
+
+Custom log function
+-------------------
+
+If you can't use ``printf`` or want to use a custom function to log, you
+can register a "logger" callback with :cpp:func:`lv_log_register_print_cb`.
+
+For example:
+
+.. code-block:: c
+
+   void my_log_cb(lv_log_level_t level, const char * buf)
+   {
+     serial_send(buf, strlen(buf));
+   }
+
+   ...
+
+
+   lv_log_register_print_cb(my_log_cb);
+
+Add logs
+********
+
+You can also use the log module via the
+``LV_LOG_TRACE/INFO/WARN/ERROR/USER(text)`` or ``LV_LOG(text)``
+functions. Here:
+
+-  ``LV_LOG_TRACE/INFO/WARN/ERROR/USER(text)`` append following information to your ``text``
+-  Log Level
+-  \__FILE\_\_
+-  \__LINE\_\_
+-  \__func\_\_
+-  ``LV_LOG(text)`` is similar to ``LV_LOG_USER`` but has no extra information attached.
+
+API
+***