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Greg has challenged some recent driver submitters on their license choices. He was correct to do so, as the choices in these instances did not always advance the aims of the submitters. But, this left submitters (and the folks who help them pick licenses) a bit confused. They have read things like Documentation/process/license-rules.rst which says: individual source files can have a different license which is required to be compatible with the GPL-2.0 and Documentation/process/submitting-drivers.rst: We don't insist on any kind of exclusive GPL licensing, and if you wish ... you may well wish to release under multiple licenses. As written, these appear a _bit_ more laissez faire than we've been in practice lately. It sounds like we at least expect submitters to make a well-reasoned license choice and to explain their rationale. It does not appear that we blindly accept anything that is simply GPLv2-compatible. Drivers appear to be the most acute source of misunderstanding, so fix the driver documentation first. Update it to clarify expectations. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: H. Peter Anvin <h.peter.anvin@intel.com> Cc: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Link: https://lore.kernel.org/r/20200814145625.8B708079@viggo.jf.intel.com Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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.. _submittingdrivers:
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Submitting Drivers For The Linux Kernel
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=======================================
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This document is intended to explain how to submit device drivers to the
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various kernel trees. Note that if you are interested in video card drivers
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you should probably talk to XFree86 (https://www.xfree86.org/) and/or X.Org
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(https://x.org/) instead.
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.. note::
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This document is old and has seen little maintenance in recent years; it
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should probably be updated or, perhaps better, just deleted. Most of
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what is here can be found in the other development documents anyway.
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Oh, and we don't really recommend submitting changes to XFree86 :)
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Also read the :ref:`Documentation/process/submitting-patches.rst <submittingpatches>`
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document.
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Allocating Device Numbers
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-------------------------
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Major and minor numbers for block and character devices are allocated
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by the Linux assigned name and number authority (currently this is
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Torben Mathiasen). The site is https://www.lanana.org/. This
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also deals with allocating numbers for devices that are not going to
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be submitted to the mainstream kernel.
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See :ref:`Documentation/admin-guide/devices.rst <admin_devices>`
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for more information on this.
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If you don't use assigned numbers then when your device is submitted it will
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be given an assigned number even if that is different from values you may
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have shipped to customers before.
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Who To Submit Drivers To
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------------------------
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Linux 2.0:
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No new drivers are accepted for this kernel tree.
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Linux 2.2:
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No new drivers are accepted for this kernel tree.
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Linux 2.4:
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If the code area has a general maintainer then please submit it to
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the maintainer listed in MAINTAINERS in the kernel file. If the
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maintainer does not respond or you cannot find the appropriate
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maintainer then please contact Willy Tarreau <w@1wt.eu>.
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Linux 2.6 and upper:
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The same rules apply as 2.4 except that you should follow linux-kernel
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to track changes in API's. The final contact point for Linux 2.6+
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submissions is Andrew Morton.
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What Criteria Determine Acceptance
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----------------------------------
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Licensing:
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The code must be released to us under the
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GNU General Public License. If you wish the driver to be
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useful to other communities such as BSD you may release
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under multiple licenses. If you choose to release under
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licenses other than the GPL, you should include your
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rationale for your license choices in your cover letter.
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See accepted licenses at include/linux/module.h
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Copyright:
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The copyright owner must agree to use of GPL.
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It's best if the submitter and copyright owner
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are the same person/entity. If not, the name of
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the person/entity authorizing use of GPL should be
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listed in case it's necessary to verify the will of
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the copyright owner.
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Interfaces:
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If your driver uses existing interfaces and behaves like
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other drivers in the same class it will be much more likely
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to be accepted than if it invents gratuitous new ones.
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If you need to implement a common API over Linux and NT
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drivers do it in userspace.
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Code:
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Please use the Linux style of code formatting as documented
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in :ref:`Documentation/process/coding-style.rst <codingStyle>`.
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If you have sections of code
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that need to be in other formats, for example because they
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are shared with a windows driver kit and you want to
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maintain them just once separate them out nicely and note
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this fact.
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Portability:
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Pointers are not always 32bits, not all computers are little
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endian, people do not all have floating point and you
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shouldn't use inline x86 assembler in your driver without
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careful thought. Pure x86 drivers generally are not popular.
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If you only have x86 hardware it is hard to test portability
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but it is easy to make sure the code can easily be made
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portable.
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Clarity:
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It helps if anyone can see how to fix the driver. It helps
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you because you get patches not bug reports. If you submit a
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driver that intentionally obfuscates how the hardware works
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it will go in the bitbucket.
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PM support:
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Since Linux is used on many portable and desktop systems, your
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driver is likely to be used on such a system and therefore it
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should support basic power management by implementing, if
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necessary, the .suspend and .resume methods used during the
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system-wide suspend and resume transitions. You should verify
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that your driver correctly handles the suspend and resume, but
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if you are unable to ensure that, please at least define the
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.suspend method returning the -ENOSYS ("Function not
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implemented") error. You should also try to make sure that your
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driver uses as little power as possible when it's not doing
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anything. For the driver testing instructions see
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Documentation/power/drivers-testing.rst and for a relatively
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complete overview of the power management issues related to
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drivers see :ref:`Documentation/driver-api/pm/devices.rst <driverapi_pm_devices>`.
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Control:
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In general if there is active maintenance of a driver by
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the author then patches will be redirected to them unless
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they are totally obvious and without need of checking.
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If you want to be the contact and update point for the
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driver it is a good idea to state this in the comments,
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and include an entry in MAINTAINERS for your driver.
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What Criteria Do Not Determine Acceptance
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-----------------------------------------
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Vendor:
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Being the hardware vendor and maintaining the driver is
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often a good thing. If there is a stable working driver from
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other people already in the tree don't expect 'we are the
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vendor' to get your driver chosen. Ideally work with the
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existing driver author to build a single perfect driver.
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Author:
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It doesn't matter if a large Linux company wrote the driver,
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or you did. Nobody has any special access to the kernel
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tree. Anyone who tells you otherwise isn't telling the
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whole story.
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Resources
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---------
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Linux kernel master tree:
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ftp.\ *country_code*\ .kernel.org:/pub/linux/kernel/...
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where *country_code* == your country code, such as
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**us**, **uk**, **fr**, etc.
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https://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git
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Linux kernel mailing list:
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linux-kernel@vger.kernel.org
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[mail majordomo@vger.kernel.org to subscribe]
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Linux Device Drivers, Third Edition (covers 2.6.10):
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https://lwn.net/Kernel/LDD3/ (free version)
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LWN.net:
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Weekly summary of kernel development activity - https://lwn.net/
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2.6 API changes:
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https://lwn.net/Articles/2.6-kernel-api/
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Porting drivers from prior kernels to 2.6:
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https://lwn.net/Articles/driver-porting/
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KernelNewbies:
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Documentation and assistance for new kernel programmers
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https://kernelnewbies.org/
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Linux USB project:
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http://www.linux-usb.org/
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How to NOT write kernel driver by Arjan van de Ven:
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http://www.fenrus.org/how-to-not-write-a-device-driver-paper.pdf
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Kernel Janitor:
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https://kernelnewbies.org/KernelJanitors
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GIT, Fast Version Control System:
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https://git-scm.com/
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