Before you begin to implement any new ideas or concepts it is always a good idea to present your plans on the U-Boot mailing list. U-Boot supports a huge amount of very different systems, and it is often impossible for the individual developer to oversee the consequences of a specific change to all architectures. Discussing concepts early can help you to avoid spending effort on code which, when submitted as a patch, might be rejected and/or will need lots of rework because it does not fit for some reason. Early peer review is an important resource - use it. Being familiar with the U-Boot Development Process is also important.
A good introduction how to prepare for submitting patches can be found in the LWN article How to Get Your Change Into the Linux Kernel as the same rules apply to U-Boot, too.
You can use a tool called patman to prepare, check and send patches. It creates change logs, cover letters and patch notes. It also simplifies the process of sending multiple versions of a series.
See more details at Patman patch manager.
General Patch Submission Rules¶
All patches must be sent to the email@example.com mailing list.
If your patch affects the code maintained by one of the Custodians, CC them when emailing your patch. The easiest way to make sure you don’t forget this even when you resubmit the patch later is to add a
Cc: name <address>line after your
Signed-off-by:line (see the example below).
Take a look at the commit logs of the files you are modifying. Authors of past commits might have input to your change, so also CC them if you think they may have feedback.
Patches should always contain exactly one complete logical change, i.e.
Changes that contain different, unrelated modifications shall be submitted as separate patches, one patch per changeset.
If one logical set of modifications affects or creates several files, all these changes shall be submitted in a single patch.
Non-functional changes, i.e. whitespace and reformatting changes, should be done in separate patches marked as
cosmetic. This separation of functional and cosmetic changes greatly facilitates the review process.
Some comments on running checkpatch.pl:
Checkpatch is a tool that can help you find some style problems, but is imperfect, and the things it complains about are of varying importance. So use common sense in interpreting the results.
Warnings that clearly only make sense in the Linux kernel can be ignored. This includes
Use #include <linux/$file> instead of <asm/$file>for example.
If you encounter warnings for existing code, not modified by your patch, consider submitting a separate, cosmetic-only patch – clearly described as such – that precedes your substantive patch.
For minor modifications (e.g. changed arguments of a function call), adhere to the present coding style of the module. Relating checkpatch warnings can be ignored in this case. A respective note in the commit or cover letter why they are ignored is desired.
Send your patches as plain text messages: no HTML, no MIME, no links, no compression, no attachments. Just plain text. The best way the generate patches is by using the
git format-patchcommand. Please use the
masterbranch of the mainline U-Boot git repository (
https://source.denx.de/u-boot/u-boot.git) as reference, unless (usually late in a release cycle) there has been an announcement to use the
nextbranch of this repository instead.
Make sure that your mailer does not mangle the patch by automatic changes like wrapping of longer lines etc. The best way to send patches is by not using your regular mail tool, but by using either
git send-emailor the
git imap-sendcommand instead. If you believe you need to use a mailing list for testing (instead of any regular mail address you own), we have a special test list for such purposes. It would be best to subscribe to the list for the duration of your tests to avoid repeated moderation - see https://lists.denx.de/listinfo/test
Choose a meaningful Subject: - keep in mind that the Subject will also be visible as headline of your commit message. Make sure the subject does not exceed 60 characters or so.
The start of the subject should be a meaningful tag (arm:, ppc:, tegra:, net:, ext2:, etc)
Include the string “PATCH” in the Subject: line of your message, e. g. “[PATCH] Add support for feature X”.
git format-patchshould automatically do this.
If you are sending a patch series composed of multiple patches, make sure their titles clearly state the patch order and total number of patches (
git format-patch -n). Also, often times an introductory email describing what the patchset does is useful (
git format-patch -n --cover-letter). As an example:
[PATCH 0/3] Add support for new SuperCPU2000 (This email does not contain a patch, just a description) [PATCH 1/3] Add core support for SuperCPU2000 [PATCH 2/3] Add support for SuperCPU2000's on-chip I2C controller [PATCH 3/3] Add support for SuperCPU2000's on-chip UART
In the message body, include a description of your changes.
For bug fixes: a description of the bug and how your patch fixes this bug. Please try to include a way of demonstrating that the patch actually fixes something.
For new features: a description of the feature and your implementation.
Additional comments which you don’t want included in U-Boot’s history can be included below the first “—” in the message body.
If your description gets too long, that’s a strong indication that you should split up your patch.
Remember that there is a size limit of 100 kB on the mailing list. In most cases, you did something wrong if your patch exceeds this limit. Think again if you should not split it into separate logical parts.
Attributing Code, Copyrights, Signing¶
Sign your changes, i. e. add a Signed-off-by: line to the message body. This can be automated by using
git commit -s. Please see the Developer Certificate of Origin section for more details here.
If you change or add significant parts to a file, then please make sure to add your copyright to that file, for example like this:
(C) Copyright 2010 Joe Hacker <firstname.lastname@example.org> Please do *not* include a detailed description of your changes. We use the *git* commit messages for this purpose.
If you add new files, please always make sure that these contain your copyright note and a GPLv2+ SPDX-License-Identifier, for example like this:
(C) Copyright 2010 Joe Hacker <email@example.com> SPDX-License-Identifier:<TAB>GPL-2.0+
If you are copying or adapting code from other projects, like the Linux kernel, or BusyBox, or similar, please make sure to state clearly where you copied the code from, and provide terse but precise information which exact version or even commit ID was used. Follow the ideas of this note from the Linux “SubmittingPatches” document:
Special note to back-porters: It seems to be a common and useful practice to insert an indication of the origin of a patch at the top of the commit message (just after the subject line) to facilitate tracking. For instance, here's what we see in 2.6-stable : Date: Tue May 13 19:10:30 2008 +0000 SCSI: libiscsi regression in 2.6.25: fix nop timer handling commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream And here's what appears in 2.4 : Date: Tue May 13 22:12:27 2008 +0200 wireless, airo: waitbusy() won't delay [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
Whatever the format, this information provides a valuable help to people tracking your trees, and to people trying to trouble-shoot bugs in your tree.
Commit message conventions¶
Please adhere to the following conventions when writing your commit log messages.
The first line of the log message is the summary line. Keep this less than 70 characters long.
Don’t use periods to end the summary line (e.g., don’t do “Add support for X.”)
Use the present tense in your summary line (e.g., “Add support for X” rather than “Added support for X”). Furthermore, use the present tense in your log message to describe what the patch is doing. This isn’t a strict rule – it’s OK to use the past tense for describing things that were happening in the old code for example.
Use the imperative tense in your summary line (e.g., “Add support for X” rather than “Adds support for X”). In general, you can think of the summary line as “this commit is meant to ‘Add support for X’”
If applicable, prefix the summary line with a word describing what area of code is being affected followed by a colon. This is a standard adopted by both U-Boot and Linux. For example, if your change affects all mpc85xx boards, prefix your summary line with “mpc85xx:”. If your change affects the PCI common code, prefix your summary line with “pci:”. The best thing to do is look at the “git log <file>” output to see what others have done so you don’t break conventions.
Insert a blank line after the summary line
For bug fixes, it’s good practice to briefly describe how things behaved before this commit
Put a detailed description after the summary and blank line. If the summary line is sufficient to describe the change (e.g. it is a trivial spelling correction or whitespace update), you can omit the blank line and detailed description.
End your log message with S.O.B. (Signed-off-by) line. This is done automatically when you use
git commit -s. Please see the Developer Certificate of Origin section for more details here.
Keep EVERY line under 72 characters. That is, your message should be line-wrapped with line-feeds. However, don’t get carried away and wrap it too short either since this also looks funny.
Detail level: The audience of the commit log message that you should cater to is those familiar with the underlying source code you are modifying, but who are _not_ familiar with the patch you are submitting. They should be able to determine what is being changed and why. Avoid excessive low-level detail. Before submitting, re-read your commit log message with this audience in mind and adjust as needed.
Sending updated patch versions¶
It is pretty normal that the first version of a patch you are submitting does not get accepted as is, and that you are asked to submit another, improved version.
When re-posting such a new version of your patch(es), please always make sure to observe the following rules.
Make an appropriate note that this is a re-submission in the subject line, e.g. “[PATCH v2] Add support for feature X”.
git format-patch --subject-prefix="PATCH v2"can be used in this case (see the example below).
Please make sure to keep a “change log”, i.e. a description of what you have changed compared to previous versions of this patch. This change log should be added below the “—” line in the patch, which starts the “comment section”, i.e. which contains text that does not get included into the actual commit message. Note: it is not sufficient to provide a change log in some cover letter that gets sent as a separate message with the patch series. The reason is that such cover letters are not as easily reviewed in our patchwork queue so they are not helpful to any reviewers using this tool. Example:
From: Joe Hacker <firstname.lastname@example.org> Date: Thu, 1 Jan 2222 12:21:22 +0200 Subject: [PATCH 1/2 v3] FOO: add timewarp-support This patch adds timewarp-support for the FOO family of processors. adapted for the current kernel structures. Signed-off-by: Joe Hacker <email@example.com> Cc: Tom Maintainer <firstname.lastname@example.org> --- Changes for v2: - Coding Style cleanup - fixed miscalculation of time-space discontinuities Changes for v3: - fixed compiler warnings observed with GCC-17.3.5 - worked around integer overflow in warp driver arch/foo/cpu/spacetime.c | 8 + drivers/warp/Kconfig | 7 + drivers/warp/Makefile | 42 +++ drivers/warp/warp-core.c | 255 +++++++++++++++++++++++++
Make sure that your mailer adds or keeps correct
References:headers, so threading of messages is working and everybody can see that the new message refers to some older posting of the same topic.
Uncommented and un-threaded repostings are extremely annoying and time-consuming, as we have to try to remember if anything similar has been posted before, look up the old threads, and then manually compare if anything has been changed, or what.
If you have problems with your e-mail client, for example because it mangles white space or wraps long lines, then please read this article about Email Clients and Patches.
U-Boot is Free Software that can redistributed and/or modified under the terms of the GNU General Public License (GPL). Currently (August 2022) version 2 of the GPL applies. Please see
Licensingfor details. To allow that later versions of U-Boot may be released under a later version of the GPL, all new code that gets added to U-Boot shall use a “GPL-2.0+” SPDX-License-Identifier.
All code must follow the U-Boot Coding Style requirements.
Before sending the patch, you must run some form of local testing. Submitting a patch that does not build or function correctly is a mistake. For non-trivial patches, either building a number of platforms locally or making use of Continuous Integration testing is strongly encouraged in order to avoid problems that can be found when attempting to merge the patch.
If you modify existing code, make sure that your new code does not add to the memory footprint of the code. Remember: Small is beautiful! When adding new features follow the guidelines laid out in System configuration.
Like some other projects, U-Boot uses Patchwork to track the state of patches. This is one of the reasons why it is mandatory to submit all patches to the U-Boot mailing list - only then they will be picked up by patchwork.
Note that Patchwork automatically tracks and collects a number of git tags from follow-up mails, so it is usually better to apply a patch through the Patchwork commandline interface than just manually applying it from a posting on the mailing list (in which case you have to do all the tracking and adding of git tags yourself). This also obviates the need of a developer to resubmit a patch only in order to collect these tags.
A Custodian has additional privileges and can:
Delegate a patch
Change the state of a patch. The following states exist:
The following are a “rule of thumb” as to how the states are used in patchwork today. Not all states are used by all custodians.
New: Patch has been submitted to the list, and none of the maintainers has changed it’s state since.
Under Review: A custodian is reviewing the patch currently.
Accepted: When a patch has been applied to a custodian repository that gets used for pulling from into upstream, they are put into “accepted” state.
Rejected: Rejected means we just don’t want to do what the patch does.
RFC: The patch is not intended to be applied to any of the mainline repositories, but merely for discussing or testing some idea or new feature.
Not Applicable: The patch either was not intended to be applied, as it was a debugging or discussion aide that patchwork picked up, or was cross-posted to our list but intended for another project entirely.
Changes Requested: The patch looks mostly OK, but requires some rework before it will be accepted for mainline.
Awaiting Upstream: A custodian may have applied this to the
nextbranch and has not merged yet to master, or has queued the patch up to be submitted to be merged, but has not yet.
Superseeded: Patches are marked as ‘superseeded’ when the poster submits a new version of these patches.
Deferred: Deferred usually means the patch depends on something else that isn’t upstream, such as patches that only apply against some specific other repository. This is also used when a patch has been in patchwork for over a year and it is unlikely to be applied as-is.
Archived: Archiving puts the patch away somewhere where it doesn’t appear in the normal pages and needs extra effort to get to.
To apply a patch from the patchwork queue using
git, download the
mbox file and apply it using:
git am file
usage: pw-am.sh <number> example: 'pw-am.sh 71002' will get and apply the patch from http://patchwork.ozlabs.org/patch/71002/
Update the state of patches¶
You have to register to be able to update the state of patches. You can use the Web interface, pwclient, or pwparser.
The pwclient command line tool can be used for example to retrieve patches, search the queue or update the state.
All necessary information for pwclient is linked from the bottom of http://patchwork.ozlabs.org/project/uboot/
for an overview on how to use it.