docs: maintainer: document expectations of small time maintainers

We appear to have a gap in our process docs. We go into detail
on how to contribute code to the kernel, and how to be a subsystem
maintainer. I can't find any docs directed towards the thousands
of small scale maintainers, like folks maintaining a single driver
or a single network protocol.

Document our expectations and best practices. I'm hoping this doc
will be particularly useful to set expectations with HW vendors.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Martin Habets <habetsm.xilinx@gmail.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20230719183225.1827100-1-kuba@kernel.org

Documentation/maintainer/feature-and-driver-maintainers.rst

@@ -0,0 +1,155 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==============================
+Feature and driver maintainers
+==============================
+
+The term "maintainer" spans a very wide range of levels of engagement
+from people handling patches and pull requests as almost a full time job
+to people responsible for a small feature or a driver.
+
+Unlike most of the chapter, this section is meant for the latter (more
+populous) group. It provides tips and describes the expectations and
+responsibilities of maintainers of a small(ish) section of the code.
+
+Drivers and alike most often do not have their own mailing lists and
+git trees but instead send and review patches on the list of a larger
+subsystem.
+
+Responsibilities
+================
+
+The amount of maintenance work is usually proportional to the size
+and popularity of the code base. Small features and drivers should
+require relatively small amount of care and feeding. Nonetheless
+when the work does arrive (in form of patches which need review,
+user bug reports etc.) it has to be acted upon promptly.
+Even when a particular driver only sees one patch a month, or a quarter,
+a subsystem could well have a hundred such drivers. Subsystem
+maintainers cannot afford to wait a long time to hear from reviewers.
+
+The exact expectations on the response time will vary by subsystem.
+The patch review SLA the subsystem had set for itself can sometimes
+be found in the subsystem documentation. Failing that as a rule of thumb
+reviewers should try to respond quicker than what is the usual patch
+review delay of the subsystem maintainer. The resulting expectations
+may range from two working days for fast-paced subsystems (e.g. networking)
+to as long as a few weeks in slower moving parts of the kernel.
+
+Mailing list participation
+--------------------------
+
+Linux kernel uses mailing lists as the primary form of communication.
+Maintainers must be subscribed and follow the appropriate subsystem-wide
+mailing list. Either by subscribing to the whole list or using more
+modern, selective setup like
+`lei <https://people.kernel.org/monsieuricon/lore-lei-part-1-getting-started>`_.
+
+Maintainers must know how to communicate on the list (plain text, no invasive
+legal footers, no top posting, etc.)
+
+Reviews
+-------
+
+Maintainers must review *all* patches touching exclusively their drivers,
+no matter how trivial. If the patch is a tree wide change and modifies
+multiple drivers - whether to provide a review is left to the maintainer.
+
+When there are multiple maintainers for a piece of code an ``Acked-by``
+or ``Reviewed-by`` tag (or review comments) from a single maintainer is
+enough to satisfy this requirement.
+
+If the review process or validation for a particular change will take longer
+than the expected review timeline for the subsystem, maintainer should
+reply to the submission indicating that the work is being done, and when
+to expect full results.
+
+Refactoring and core changes
+----------------------------
+
+Occasionally core code needs to be changed to improve the maintainability
+of the kernel as a whole. Maintainers are expected to be present and
+help guide and test changes to their code to fit the new infrastructure.
+
+Bug reports
+-----------
+
+Maintainers must ensure severe problems in their code reported to them
+are resolved in a timely manner: regressions, kernel crashes, kernel warnings,
+compilation errors, lockups, data loss, and other bugs of similar scope.
+
+Maintainers furthermore should respond to reports about other kinds of
+bugs as well, if the report is of reasonable quality or indicates a
+problem that might be severe -- especially if they have *Supported*
+status of the codebase in the MAINTAINERS file.
+
+Selecting the maintainer
+========================
+
+The previous section described the expectations of the maintainer,
+this section provides guidance on selecting one and describes common
+misconceptions.
+
+The author
+----------
+
+Most natural and common choice of a maintainer is the author of the code.
+The author is intimately familiar with the code, so it is the best person
+to take care of it on an ongoing basis.
+
+That said, being a maintainer is an active role. The MAINTAINERS file
+is not a list of credits (in fact a separate CREDITS file exists),
+it is a list of those who will actively help with the code.
+If the author does not have the time, interest or ability to maintain
+the code, a different maintainer must be selected.
+
+Multiple maintainers
+--------------------
+
+Modern best practices dictate that there should be at least two maintainers
+for any piece of code, no matter how trivial. It spreads the burden, helps
+people take vacations and prevents burnout, trains new members of
+the community etc. etc. Even when there is clearly one perfect candidate,
+another maintainer should be found.
+
+Maintainers must be human, therefore, it is not acceptable to add a mailing
+list or a group email as a maintainer. Trust and understanding are the
+foundation of kernel maintenance and one cannot build trust with a mailing
+list. Having a mailing list *in addition* to humans is perfectly fine.
+
+Corporate structures
+--------------------
+
+To an outsider the Linux kernel may resemble a hierarchical organization
+with Linus as the CEO. While the code flows in a hierarchical fashion,
+the corporate template does not apply here. Linux is an anarchy held
+together by (rarely expressed) mutual respect, trust and convenience.
+
+All that is to say that managers almost never make good maintainers.
+The maintainer position more closely matches an on-call rotation
+than a position of power.
+
+The following characteristics of a person selected as a maintainer
+are clear red flags:
+
+ - unknown to the community, never sent an email to the list before
+ - did not author any of the code
+ - (when development is contracted) works for a company which paid
+   for the development rather than the company which did the work
+
+Non compliance
+==============
+
+Subsystem maintainers may remove inactive maintainers from the MAINTAINERS
+file. If the maintainer was a significant author or played an important
+role in the development of the code, they should be moved to the CREDITS file.
+
+Removing an inactive maintainer should not be seen as a punitive action.
+Having an inactive maintainer has a real cost as all developers have
+to remember to include the maintainers in discussions and subsystem
+maintainers spend brain power figuring out how to solicit feedback.
+
+Subsystem maintainers may remove code for lacking maintenance.
+
+Subsystem maintainers may refuse accepting code from companies
+which repeatedly neglected their maintainership duties.

Documentation/maintainer/index.rst

@@ -9,6 +9,7 @@ additions to this manual.
 .. toctree::
    :maxdepth: 2
 
+   feature-and-driver-maintainers
    configure-git
    rebasing-and-merging
    pull-requests