U-Boot Coding Style
The following Coding Style requirements shall be mandatory for all code contributed to
the U-Boot project.
Exceptions are only allowed if code from other projects is integrated with no
or only minimal changes.
The following rules apply:
- All contributions to U-Boot should conform to the Linux kernel
coding style; see the file
and the script
in your Linux kernel source
- Use patman to send your patches ('tools/patman/patman -H' for full instructions). With a few tags in your commits this will check your patches and take care of emailing them.
- If you don't use patman, make sure to run the checkpatch.pl
script from the Linux source tree to check your patches. See also Patches for more comments on this tool.
Note that this should be done before posting on the mailing list!
- Source files originating from different projects (for example
the MTD subsystem or the hush shell code from the BusyBox
project) may, after careful consideration, be exempted from
these rules. For such files, the original coding style may be
kept to ease subsequent migration to newer versions of those
- Please note that U-Boot is implemented in C (and to some small
parts in Assembler); no C++ is used, so please do not use C++
style comments (//) in your code.
- Please also stick to the following formatting rules:
- Remove any trailing white space
- Use TAB characters for indentation
and vertical alignment, not spaces
- Make sure NOT to use DOS '\r\n' line feeds
- Do not add more than 2 consecutive empty lines to source files
- Do not add trailing empty lines to source files
- Using the option
git config --global color.diff auto will help
to visually see whitespace problems in
diff output from
- In Emacs one can use
M-x whitespace-global-mode to get visual
feedback on the nasty details.
M-x whitespace-cleanup does The Right Thing
Submissions of new code or patches that do not conform to these
requirements shall be rejected with a request to reformat the
U-Boot Code Documentation
U-Boot adopted the kernel-doc annotation style, this is the only exception from
multi-line comment rule of Coding Style. While not mandatory, adding
documentation is strongly advised. The Linux kernel kernel-doc document
applies with no changes.
Use structures for I/O access
U-Boot typically uses a C structure to map out the registers in an I/O region, rather than offsets. The reasons for this are:
- It dissociates the register location (offset) from the register
type, which means the developer has to make sure the type is
right for each access, whereas with the struct method, this is
checked by the compiler;
- It avoids actually writing all offsets, which is (more) error-
- It allows for better compile time sanity-checking of values we write to registers.
This may need to change to
the kernel model if we allow for more run-time detection of what drivers
are appropriate for what we're running on.