[patch 2/2] Documentation/process: Add tip tree handbook

[Thomas Gleixner <tglx@linutronix.de>]

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Add a document to the subsystem/maintainer handbook section, which explains
what the tip tree is, how it operates and what rules and expectations it
has.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 Documentation/process/maintainer-handbooks.rst |    2 
 Documentation/process/maintainer-tip.rst       |  796 +++++++++++++++++++++++++
 2 files changed, 798 insertions(+)

--- a/Documentation/process/maintainer-handbooks.rst
+++ b/Documentation/process/maintainer-handbooks.rst
@@ -12,3 +12,5 @@ which is supplementary to the general de
 .. toctree::
    :numbered:
    :maxdepth: 2
+
+   maintainer-tip
--- /dev/null
+++ b/Documentation/process/maintainer-tip.rst
@@ -0,0 +1,796 @@
+The tip tree handbook
+=====================
+
+What is the tip tree?
+---------------------
+
+The tip tree is a collection of several subsystems and areas of
+development. The tip tree is both a direct development tree and a
+aggregation tree for several sub-maintainer trees. The tip tree gitweb URL
+is: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
+
+The tip tree contains the following subsystems:
+
+   - **x86 architecture**
+
+     The x86 architecture development takes place in the tip tree except
+     for the x86 KVM and XEN specific parts which are maintained in the
+     corresponding subsystems and routed directly to mainline from
+     there. It's still good practice to Cc the x86 maintainers on
+     x86-specific KVM and XEN patches.
+
+     Some x86 subsystems have their own maintainers in addition to the
+     overall x86 maintainers.  Please Cc the overall x86 maintainers on
+     patches touching files in arch/x86 even when they are not called out
+     by the MAINTAINER file.
+
+     Note, that ``x86@kernel.org`` is not a mailing list. It is merely a
+     mail alias which distributes mails to the x86 top-level maintainer
+     team. Please always Cc the Linux Kernel mailing list (LKML)
+     ``linux-kernel@vger.kernel.org``, otherwise your mail ends up only in
+     the private inboxes of the maintainers.
+
+   - **Scheduler**
+
+   - **Locking and atomics**
+
+   - **Generic interrupt subsystem and interrupt chip drivers**:
+
+     - interrupt core development happens in the irq/core branch
+
+     - interrupt chip driver development happens also in the irq/core
+       branch, but the patches are mostly applied in a separate maintainer
+       tree and then aggregated into irq/core
+
+   - **Time, timers, timekeeping, NOHZ and related chip drivers**:
+
+     - timekeeping, clocksource core, NTP and alarmtimer development
+       happens in the timers/core branch, but patches are mostly applied in
+       a separate maintainer tree and then aggregated into timers/core
+
+     - clocksource/event driver development happens in the timers/core
+       branch, but patches are mostly applied in a separate maintainer tree
+       and then aggregated into timers/core
+
+   - **Performance counters core, architecture support and tooling**:
+
+     - perf core and architecture support development happens in the
+       perf/core branch
+
+     - perf tooling development happens in the perf tools maintainer
+       tree and is aggregated into the tip tree.
+
+   - **CPU hotplug core**
+
+   - **RAS core**
+
+   - **EFI core**
+
+     EFI development in the efi git tree. The collected patches are
+     aggregated in the tip efi/core branch.
+
+   - **RCU**
+
+     RCU development happens in the linux-rcu tree. The resulting changes
+     are aggregated into the tip core/rcu branch.
+
+   - **Various core code components**:
+
+       - debugobjects
+
+       - objtool
+
+       - random bits and pieces
+
+
+Patch submission notes
+----------------------
+
+Selecting the tree/branch
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+In general, development against the head of the tip tree master branch is
+fine, but for the subsystems which are maintained separately, have their
+own git tree and are only aggregated into the tip tree, development should
+take place against the relevant subsystem tree or branch.
+
+Bug fixes which target mainline should always be applicable against the
+mainline kernel tree. Potential conflicts against changes which are already
+queued in the tip tree are handled by the maintainers.
+
+Patch subject
+^^^^^^^^^^^^^
+
+The tip tree preferred format for patch subject prefixes is
+'subsys/component:', e.g. 'x86/apic:', 'x86/mm/fault:', 'sched/fair:',
+'genirq/core:'. Please do not use file names or complete file paths as
+prefix. 'git log path/to/file' should give you a reasonable hint in most
+cases.
+
+The condensed patch description in the subject line should start with a
+uppercase letter and should be written in imperative tone.
+
+
+Changelog
+^^^^^^^^^
+
+The general rules about changelogs in the process documentation, see
+:ref:`Documentation/process/ <submittingpatches>`, apply.
+
+The tip tree maintainers set value on following these rules, especially on
+the request to write changelogs in imperative mood and not impersonating
+code or the execution of it. This is not just a whim of the
+maintainers. Changelogs written in abstract words are more precise and
+tend to be less confusing than those written in the form of novels.
+
+It's also useful to structure the changelog into several paragraphs and not
+lump everything together into a single one. A good structure is to explain
+the context, the problem and the solution in separate paragraphs and this
+order.
+
+Examples for illustration:
+
+  Example 1::
+
+    x86/intel_rdt/mbm: Fix MBM overflow handler during hot cpu
+
+    When a CPU is dying, we cancel the worker and schedule a new worker on a
+    different CPU on the same domain. But if the timer is already about to
+    expire (say 0.99s) then we essentially double the interval.
+
+    We modify the hot cpu handling to cancel the delayed work on the dying
+    cpu and run the worker immediately on a different cpu in same domain. We
+    donot flush the worker because the MBM overflow worker reschedules the
+    worker on same CPU and scans the domain->cpu_mask to get the domain
+    pointer.
+
+  Improved version::
+
+    x86/intel_rdt/mbm: Fix MBM overflow handler during CPU hotplug
+
+    When a CPU is dying, the overflow worker is canceled and rescheduled on a
+    different CPU in the same domain. But if the timer is already about to
+    expire this essentially doubles the interval which might result in a non
+    detected overflow.
+
+    Cancel the overflow worker and reschedule it immediately on a different CPU
+    in the same domain. The work could be flushed as well, but that would
+    reschedule it on the same CPU.
+
+  Example 2::
+
+    time: POSIX CPU timers: Ensure that variable is initialized
+
+    If cpu_timer_sample_group returns -EINVAL, it will not have written into
+    *sample. Checking for cpu_timer_sample_group's return value precludes the
+    potential use of an uninitialized value of now in the following block.
+    Given an invalid clock_idx, the previous code could otherwise overwrite
+    *oldval in an undefined manner. This is now prevented. We also exploit
+    short-circuiting of && to sample the timer only if the result will
+    actually be used to update *oldval.
+
+  Improved version::
+
+    posix-cpu-timers: Make set_process_cpu_timer() more robust
+
+    Because the return value of cpu_timer_sample_group() is not checked,
+    compilers and static checkers can legitimately warn about a potential use
+    of the uninitialized variable 'now'. This is not a runtime issue as all
+    call sites hand in valid clock ids.
+
+    Also cpu_timer_sample_group() is invoked unconditionally even when the
+    result is not used because *oldval is NULL.
+
+    Make the invocation conditional and check the return value.
+
+  Example 3::
+
+    The entity can also be used for other purposes.
+
+    Let's rename it to be more generic.
+
+  Improved version::
+
+    The entity can also be used for other purposes.
+
+    Rename it to be more generic.
+
+
+For complex scenarios, especially race conditions and memory ordering
+issues, it is valuable to depict the scenario with a table which shows
+the parallelism and the temporal order of events. Here is an example::
+
+    CPU0                            CPU1
+    free_irq(X)                     interrupt X
+                                    spin_lock(desc->lock)
+                                    wake irq thread()
+                                    spin_unlock(desc->lock)
+    spin_lock(desc->lock)
+    remove action()
+    shutdown_irq()
+    release_resources()             thread_handler()
+    spin_unlock(desc->lock)           access released resources.
+                                      ^^^^^^^^^^^^^^^^^^^^^^^^^
+    synchronize_irq()
+
+Lockdep provides similar useful output to depict a possible deadlock
+scenario::
+
+    CPU0                                    CPU1
+    rtmutex_lock(&rcu->rt_mutex)
+      spin_lock(&rcu->rt_mutex.wait_lock)
+                                            local_irq_disable()
+                                            spin_lock(&timer->it_lock)
+                                            spin_lock(&rcu->mutex.wait_lock)
+    --> Interrupt
+        spin_lock(&timer->it_lock)
+
+
+Function references in changelogs
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+When a function is mentioned in the changelog, either the text body or the
+subject line, please use the format 'function_name()'. Omitting the
+brackets after the function name can be ambiguous::
+
+  Subject: subsys/component: Make reservation_count static
+
+  reservation_count is only used in reservation_stats. Make it static.
+
+The variant with brackets is more precise::
+
+  Subject: subsys/component: Make reservation_count() static
+
+  reservation_count() is only called from reservation_stats(). Make it
+  static.
+
+
+Backtraces in changelogs
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Backtraces can be useful to document the call chain which led to a
+problem. Though not all back traces are really valuable because the call
+chain is unique and obvious, e.g. in early boot code. Just copying the full
+dmesg output is adding a lot of distracting information like timestamps,
+module lists, register and stack dumps etc.
+
+Reducing the backtrace to the real relevant data helps to concentrate on
+the issue and not being distracted by destilling the relevant information
+out of the dump. Here is an example of a well trimmed backtrace::
+
+  unchecked MSR access error: WRMSR to 0xd51 (tried to write 0x0000
+  000000000064) at rIP: 0xffffffffae059994 (native_write_msr+0x4/0x20)
+  Call Trace:
+  mba_wrmsr+0x41/0x80
+  update_domains+0x125/0x130
+  rdtgroup_mkdir+0x270/0x500
+
+
+Ordering of commit tags
+^^^^^^^^^^^^^^^^^^^^^^^
+
+To have a uniform view of the commit tags, the tip maintainers use the
+following tag ordering scheme:
+
+ - Fixes: 12char-SHA1 ("sub/sys: Original subject line")
+
+   A Fixes tag should be added even for changes which do not need to be
+   backported to stable kernels, i.e. when addressing a recently introduced
+   issue which only affects tip or the current head of mainline. These tags
+   are helpful to identify the original commit and are much more valuable
+   than prominently mentioning the commit which introduced a problem in the
+   text of the changelog itself because they can be automatically
+   extracted.
+
+   The following example illustrates the difference::
+
+     Commit
+
+       abcdef012345678 ("x86/xxx: Replace foo with bar")
+
+     left an unused instance of variable foo around. Remove it.
+
+     Signed-off-by: J.Dev <j.dev@mail>
+
+   Please say instead::
+
+     The recent replacement of foo with bar left an unused instance of
+     variable foo around. Remove it.
+
+     Fixes: abcdef012345678 ("x86/xxx: Replace foo with bar")
+     Signed-off-by: J.Dev <j.dev@mail>
+
+   The latter puts the information about the patch into the focus and
+   amends it with the reference to the commit which introduced the issue
+   rather than putting the focus on the original commit in the first place.
+
+ - Reported-by: ``Reporter <reporter@mail>``
+
+ - Originally-by: ``Original author <original-author@mail>``
+
+ - Suggested-by: ``Suggester <suggester@mail>``
+
+ - Co-developed-by: ``Co-author <co-author@mail>``
+
+   Signed-off: ``Co-author <co-author@mail>``
+
+   Note, that Co-developed-by and Signed-off-by of the co-author(s) must
+   come in pairs.
+
+ - Signed-off-by: ``Author <author@mail>``
+
+   The first Signed-off-by (SOB) after the last Co-developed-by/SOB pair is the
+   author SOB, i.e. the person flagged as author by git.
+
+ - Signed-off-by: ``Patch handler <handler@mail>``
+
+   SOBs after the author SOB are from people handling and transporting the
+   patch, but were not involved in development. If the handler made
+   modifications to the patch or the changelog, then this should be
+   mentioned **after** the changelog text and **above** all commit tags in
+   the following format::
+
+     ... changelog text ends.
+
+     [ handler: Replaced foo by bar and updated changelog ]
+
+     First-tag: .....
+
+   Note the two empty new lines which separate the changelog text and the
+   commit tags from that notice.
+
+   If a patch is sent to the mailing list by a handler then the author has
+   to be noted in the first line of the changelog with::
+
+     From: ``Author <author@mail>``
+
+     Changelog text starts here....
+
+   so the authorship is preserved. The 'From:' line has to be followed by a
+   empty newline. If that 'From:' line is missing, then the patch would be
+   attributed to the person who sent (transported) it. The 'From:' line is
+   automatically removed when the patch is applied and does not show up in
+   the final git changelog. It merely affects the authorship information of
+   the resulting git commit.
+
+ - Tested-by: ``Tester <tester@mail>``
+
+ - Reviewed-by: ``Reviewer <reviewer@mail>``
+
+ - Acked-by: ``Acker <acker@mail>``
+
+ - Cc: ``cc-ed-person <person@mail>``
+
+   If the patch should be backported to stable, then please add a '``Cc:
+   stable@vger.kernel.org``' tag, but do not Cc stable when sending your
+   mail.
+
+ - Link: ``https://link/to/information``
+
+   For referring to email on LKML or other kernel mailing lists, please use
+   the lkml.kernel.org redirector URL::
+
+     https://lkml.kernel.org/r/email-message@id
+
+   The kernel.org redirector is considered a stable URL unlike other email
+   archives.
+
+   Maintainers will add a Link tag referencing the email of the patch
+   submission when they apply a patch to the tip tree. This tag is useful
+   for later reference and is also used for commit notifications.
+
+Please do not use combined tags, e.g. Reported-and-tested-by, as they just
+complicate automated extraction of tags.
+
+
+Links to documentation
+^^^^^^^^^^^^^^^^^^^^^^
+
+Providing links to documentation in the changelog is a great help to later
+debugging and analysis.  Unfortunately, URLs often break very quickly
+because companies restructure their websites frequently.  Non-'volatile'
+exceptions include the Intel SDM and the AMD APM.
+
+Therefore, for 'volatile' documents, please create an entry in the kernel
+bugzilla https://bugzilla.kernel.org and attach a copy of these documents
+to the bugzilla entry. Finally, provide the URL of the bugzilla entry in
+the changelog.
+
+
+Patch version information
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+When sending a new modified version of a patch or a patch series please put
+a version number into the '[PATCH]' part of the subject line::
+
+  Subject: [PATCH V2] sub/sys: Condensed patch summary
+
+  Subject: [PATCH V2 M/N] sub/sys: Condensed patch summary
+
+It's good practice to include information about the changes between
+versions of patches into the cover letter and the changelogs of the
+individual patches.
+
+Please put this information **after** the '- - -' line which separates the
+changelog from the rest of the patch. The version information is not part
+of the changelog which gets committed to the git tree. It is additional
+information for the reviewers. If it's placed above the commit tags, it
+needs manual interaction to remove it. If it is below the separator line it
+gets automatically stripped off when applying the patch::
+
+  ...
+  Signed-off-by: Author <author@mail>
+  ---
+  V2 -> V3: Removed redundant helper function
+  V1 -> V2: Cleaned up coding style and addressed review comments
+
+  path/to/file | 5+++--
+  ...
+
+Patch resend or reminders
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The maintainers try to process patches in a timely manner, although it is
+not always possible to respond within a short time period.  Furthermore,
+from time to time patches can be lost or misplaced, so that a reminder or a
+resend is appropriate.
+
+Please wait at least a week or two before replying to your patch or cover
+letter with a gentle reminder on the mailing list.
+
+It's also ok to resend the patch or the patch series after a couple of
+weeks with the word 'RESEND' added to the subject line::
+
+   [PATCH Vx RESEND] sub/sys: Condensed patch summary
+
+Don't add RESEND when you are submitting a modified version of a patch or a
+patch series. RESEND only applies for resubmission of a non-modified patch
+or patch series.
+
+
+Merge window
+^^^^^^^^^^^^
+
+Please do not expect large patch series to be handled during the merge
+window or even during the week before.  Such patches should be submitted in
+mergeable state *at* *least* a week before the merge window opens.
+Exceptions are made for bug fixes and *sometimes* for small standalone
+drivers for new hardware or minimally invasive patches for hardware
+enablement.
+
+During the merge window, the maintainers instead focus on following the
+upstream changes, fixing merge window fallout, collecting bug fixes, and
+allowing themselves a breath. Please respect that.
+
+The release candidate -rc1 is the starting point for new patches to be
+applied which are targeted for the next merge window.
+
+
+Git
+^^^
+
+The tip maintainers accept git pull requests from maintainers who provide
+subsystem changes for aggregation in the tip tree.
+
+Pull requests for new patch submissions are usually not accepted and do not
+replace proper patch submission to the mailing list. The main reason for
+this is that the review workflow is email based.
+
+If you submit a larger patch series it is helpful to provide a git branch
+in a private repository which allows interested people to easily pull the
+series for testing. The usual way to offer this is a git URL in the cover
+letter of the patch series.
+
+
+Coding style notes
+------------------
+
+Comment style
+^^^^^^^^^^^^^
+
+Sentences in comments start with a uppercase letter.
+
+Single line comments::
+
+	/* This is a single line comment */
+
+Multi-line comments::
+
+	/*
+	 * This is a properly formatted
+	 * multi-line comment.
+	 *
+	 * Larger multi-line comments should be split into paragraphs.
+	 */
+
+No tail comments:
+
+  Please refrain from using tail comments. Tail comments disturb the
+  reading flow in almost all contexts, but especially in code::
+
+  	if (somecondition_is_true) /* Don't put a comment here */
+		dostuff(); /* Neither here */
+
+	seed = MAGIC_CONSTANT; /* Nor here */
+
+  Use freestanding comments instead::
+
+	/* This condition is not obvious without a comment */
+	if (somecondition_is_true) {
+		/* This really needs to be documented */
+		dostuff();
+	}
+
+	/* This magic initialization needs a comment. Maybe not? */
+	seed = MAGIC_CONSTANT;
+
+Comment the important things:
+
+  Comments should be added where the operation is not obvious. Documenting
+  the obvious is just a distraction::
+
+  	/* Decrement refcount and check for zero */
+	if (refcount_dec_and_test(&p->refcnt)) {
+		do;
+		lots;
+		of;
+		magic;
+		things;
+	}
+
+  Instead comments should explain the non-obvious details and document
+  constraints::
+
+	if (refcount_dec_and_test(&p->refcnt)) {
+		/*
+		 * Really good explanation why the magic things below
+		 * need to be done, ordering and locking constraints,
+		 * etc..
+		 */
+		do;
+		lots;
+		of;
+		magic;
+		/* Needs to be the last operation because ... */
+		things;
+	}
+
+Function documentation comments:
+
+  To document functions and their arguments please use kernel-doc format
+  and not free form comments::
+
+  	/**
+	 * magic_function - Do lots of magic stuff
+	 * @magic:	Pointer to the magic data to operate on
+	 * @offset:	Offset in the data array of @magic
+	 *
+	 * Deep explanation of mysterious things done with @magic along
+         * with documentation of the return values.
+	 *
+	 * Note, that the argument descriptors above are arranged
+	 * in a tabular fashion.
+	 */
+
+  This applies especially for globally visible functions and inline
+  functions in public header files. It might be overkill to use kernel-doc
+  format for every (static) function which needs a tiny explanation. The
+  usage of descriptive function names often replaces these tiny comments.
+  Apply common sense as always.
+
+
+Bracket rules
+^^^^^^^^^^^^^
+
+Brackets should be omitted only if the statement which follows 'if', 'for',
+'while' etc. is truly a single line::
+
+	if (foo)
+		do_something();
+
+The following is not considered to be a single line statement even
+though C does not require brackets::
+
+	for (i = 0; i < end; i++)
+		if (foo[i])
+			do_something(foo[i]);
+
+Adding brackets around the outer loop enhances the reading flow::
+
+	for (i = 0; i < end; i++) {
+		if (foo[i])
+			do_something(foo[i]);
+	}
+
+
+Variable declarations
+^^^^^^^^^^^^^^^^^^^^^
+
+The preferred ordering of variable declarations at the beginning of a
+function is reverse fir tree order::
+
+	struct long_struct_name *descriptive_name;
+	unsigned long foo, bar;
+	unsigned int tmp;
+	int ret;
+
+The above is faster to parse than the reverse ordering::
+
+	int ret;
+	unsigned int tmp;
+	unsigned long foo, bar;
+	struct long_struct_name *descriptive_name;
+
+And even more so than random ordering::
+
+	unsigned long foo, bar;
+	int ret;
+	struct long_struct_name *descriptive_name;
+	unsigned int tmp;
+
+Also please try to aggregate variables of the same type into a single
+line. There is no point in wasting screen space::
+
+	unsigned long a;
+	unsigned long b;
+	unsigned long c;
+	unsigned long d;
+
+It's really sufficient to do::
+
+	unsigned long a, b, c, d;
+
+Please also refrain from introducing line splits in variable declarations::
+
+	struct long_struct_name *descriptive_name = container_of(bar,
+						      struct long_struct_name,
+	                                              member);
+	struct foobar foo;
+
+It's way better to move the initialization to a separate line after the
+declarations::
+
+	struct long_struct_name *descriptive_name;
+	struct foobar foo;
+
+	descriptive_name = container_of(bar, struct long_struct_name, member);
+
+
+Variable types
+^^^^^^^^^^^^^^
+
+Please use the proper u8, u16, u32, u64 types for variables which are meant
+to describe hardware or are used as arguments for functions which access
+hardware. These types are clearly defining the bit width and avoid
+truncation, expansion and 32/64 bit confusion.
+
+u64 is also recommended in code which would become ambiguous for 32bit when
+'unsigned long' would be used instead. While in such situations 'unsigned
+long long' could be used as well, u64 is shorter and also clearly shows
+that the operation is required to be 64bit wide independent of the target
+CPU.
+
+Please use 'unsigned int' instead of 'unsigned'.
+
+
+Constants
+^^^^^^^^^
+
+Please do not use literal (hexa)decimal numbers in code or initializers.
+Either use proper defines which have descriptive names or consider using
+an enum.
+
+
+Struct declarations and initializers
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Struct declarations should align the struct member names in a tabular
+fashion::
+
+	struct bar_order {
+		unsigned int	guest_id;
+		int		ordered_item;
+		struct menu	*menu;
+	};
+
+Please avoid documenting struct members within the declaration, because
+this often results in strangely formatted comments and the struct members
+become obfuscated::
+
+ 	struct bar_order {
+  		unsigned int	guest_id; /* Unique guest id */
+		int		ordered_item;
+		/* Pointer to a menu instance which contains all the drinks */
+		struct menu	*menu;
+	};
+
+Instead, please consider using the kernel-doc format in a comment preceding
+the struct declaration, which is easier to read and has the added advantage
+of including the information in the kernel documentation, for example, as
+follows::
+
+
+	/**
+	 * struct bar_order - Description of a bar order
+	 * @guest_id:		Unique guest id
+	 * @ordered_item:	The item number from the menu
+	 * @menu:		Pointer to the menu from which the item
+	 *  			was ordered
+	 *
+	 * Supplementary information for using the struct.
+	 *
+	 * Note, that the struct member descriptors above are arranged
+	 * in a tabular fashion.
+	 */
+	struct bar_order {
+		unsigned int	guest_id;
+		int		ordered_item;
+		struct menu	*menu;
+	};
+
+Static struct initializers must use C99 initializers and should also be
+aligned in a tabular fashion::
+
+	static struct foo statfoo = {
+		.a		= 0,
+		.plain_integer	= CONSTANT_DEFINE_OR_ENUM,
+		.bar		= &statbar,
+	};
+
+
+Line breaks
+^^^^^^^^^^^
+
+Restricting line length to 80 characters makes deeply indented code hard to
+read.  Consider breaking out code into helper functions to avoid excessive
+line breaking.
+
+The 80 character rule is not a strict rule, so please use common sense when
+breaking lines. Especially format strings should never be broken up.
+
+When splitting function declarations or function calls, then please align
+the first argument in the second line with the first argument in the first
+line::
+
+  static int long_function_name(struct foobar *barfoo, unsigned int id,
+  				unsigned int offset)
+  {
+
+  	if (!id) {
+		ret = longer_function_name(barfoo, DEFAULT_BARFOO_ID,
+					   offset);
+	...
+
+Namespaces
+^^^^^^^^^^
+
+To improve readability and to allow easy grepping for information the usage
+of consistent namespaces is important. The namespace should be used as a
+prefix for globally visible (inline) functions and variables. A simple rule
+for chosing a namespace prefix is to combine the subsystem and the
+component name, e.g. 'x86_comp\_', 'sched\_', 'irq\_', 'mutex\_', etc. For
+static functions and variables the namespace prefix can be omitted.
+
+Also be careful when using vendor names in namespaces. There is no value of
+having 'xxx_vendor\_' or 'vendor_xxx_` as prefix for all static functions
+of a vendor specific file as it is already clear that the code is vendor
+specific. Aside of that vendor names should only be used when it is really
+vendor specific functionality.
+
+As always apply common sense and aim for consistency and readability.
+
+
+Commit notifications
+--------------------
+
+The tip tree is monitored by a bot for new commits. The bot sends an email
+for each new commit to a dedicated mailing list
+(``linux-tip-commits@vger.kernel.org``) and Cc's all people who are
+mentioned in one of the commit tags. It uses the email message id from the
+Link tag at the end of the tag list to set the In-Reply-To email header so
+the message is properly threaded with the patch submission email.
+
+The maintainers try to reply to the submitter when merging a patch, but
+they sometimes forget or it does not fit the workflow of the moment. While
+the bot message is purely mechanical assume it implies a 'Thank you!
+Applied.'.