Without the units these numbers are confusing. Add a comment about the
unit being 'bytes' and mention 'buildman' as the source.

Suggested-by: Lukasz Majewski <lukma@denx.de>
Signed-off-by: Simon Glass <sjg@chromium.org>

The EFI implementation does not fit into any of the existing categories.

Provide LOGC_EFI so that EFI related message can be filtered.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>

When functions return an error it propagates up the stack to the point
where it is reported. Often the error code provides enough information
about the root cause of the error that this is obvious what went wrong.

However in some cases the error may be hard to trace. For example if a
driver uses several devices to perform an operation, it may not be
obvious which one failed.

Add a log_ret() macro to help with this. This can be used to wrap any
error-return value. The logging system will then output a log record when
the original error is generated, making it easy to trace the call stack
of the error.

This macro can significantly impact code size, so its use is controlled
by a Kconfig option, which is enabled for sandbox.

Signed-off-by: Simon Glass <sjg@chromium.org>

Add some notes about recent new features.

Signed-off-by: Simon Glass <sjg@chromium.org>

Add documentation for the log system.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>