Adding upstream version 9.1.upstream/9.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1251 insertions, 0 deletions

diff --git a/doc/developer/checkpatch.rst b/doc/developer/checkpatch.rst
new file mode 100644
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@@ -0,0 +1,1251 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+
+.. _checkpatch:
+
+==========
+Checkpatch
+==========
+
+Checkpatch (scripts/checkpatch.pl) is a perl script which checks for trivial
+style violations in patches and optionally corrects them.  Checkpatch can
+also be run on file contexts and without the kernel tree.
+
+Checkpatch is not always right. Your judgement takes precedence over checkpatch
+messages.  If your code looks better with the violations, then its probably
+best left alone.
+
+
+Options
+=======
+
+This section will describe the options checkpatch can be run with.
+
+Usage::
+
+  ./scripts/checkpatch.pl [OPTION]... [FILE]...
+
+Available options:
+
+ - -q,  --quiet
+
+   Enable quiet mode.
+
+ - -v,  --verbose
+   Enable verbose mode.  Additional verbose test descriptions are output
+   so as to provide information on why that particular message is shown.
+
+ - --no-tree
+
+   Run checkpatch without the kernel tree.
+
+ - --no-signoff
+
+   Disable the 'Signed-off-by' line check.  The sign-off is a simple line at
+   the end of the explanation for the patch, which certifies that you wrote it
+   or otherwise have the right to pass it on as an open-source patch.
+
+   Example::
+
+	 Signed-off-by: Random J Developer <random@developer.example.org>
+
+   Setting this flag effectively stops a message for a missing signed-off-by
+   line in a patch context.
+
+ - --patch
+
+   Treat FILE as a patch.  This is the default option and need not be
+   explicitly specified.
+
+ - --emacs
+
+   Set output to emacs compile window format.  This allows emacs users to jump
+   from the error in the compile window directly to the offending line in the
+   patch.
+
+ - --terse
+
+   Output only one line per report.
+
+ - --showfile
+
+   Show the diffed file position instead of the input file position.
+
+ - -g,  --git
+
+   Treat FILE as a single commit or a git revision range.
+
+   Single commit with:
+
+   - <rev>
+   - <rev>^
+   - <rev>~n
+
+   Multiple commits with:
+
+   - <rev1>..<rev2>
+   - <rev1>...<rev2>
+   - <rev>-<count>
+
+ - -f,  --file
+
+   Treat FILE as a regular source file.  This option must be used when running
+   checkpatch on source files in the kernel.
+
+ - --subjective,  --strict
+
+   Enable stricter tests in checkpatch.  By default the tests emitted as CHECK
+   do not activate by default.  Use this flag to activate the CHECK tests.
+
+ - --list-types
+
+   Every message emitted by checkpatch has an associated TYPE.  Add this flag
+   to display all the types in checkpatch.
+
+   Note that when this flag is active, checkpatch does not read the input FILE,
+   and no message is emitted.  Only a list of types in checkpatch is output.
+
+ - --types TYPE(,TYPE2...)
+
+   Only display messages with the given types.
+
+   Example::
+
+     ./scripts/checkpatch.pl mypatch.patch --types EMAIL_SUBJECT,BRACES
+
+ - --ignore TYPE(,TYPE2...)
+
+   Checkpatch will not emit messages for the specified types.
+
+   Example::
+
+     ./scripts/checkpatch.pl mypatch.patch --ignore EMAIL_SUBJECT,BRACES
+
+ - --show-types
+
+   By default checkpatch doesn't display the type associated with the messages.
+   Set this flag to show the message type in the output.
+
+ - --max-line-length=n
+
+   Set the max line length (default 100).  If a line exceeds the specified
+   length, a LONG_LINE message is emitted.
+
+
+   The message level is different for patch and file contexts.  For patches,
+   a WARNING is emitted.  While a milder CHECK is emitted for files.  So for
+   file contexts, the --strict flag must also be enabled.
+
+ - --min-conf-desc-length=n
+
+   Set the Kconfig entry minimum description length, if shorter, warn.
+
+ - --tab-size=n
+
+   Set the number of spaces for tab (default 8).
+
+ - --root=PATH
+
+   PATH to the kernel tree root.
+
+   This option must be specified when invoking checkpatch from outside
+   the kernel root.
+
+ - --no-summary
+
+   Suppress the per file summary.
+
+ - --mailback
+
+   Only produce a report in case of Warnings or Errors.  Milder Checks are
+   excluded from this.
+
+ - --summary-file
+
+   Include the filename in summary.
+
+ - --debug KEY=[0|1]
+
+   Turn on/off debugging of KEY, where KEY is one of 'values', 'possible',
+   'type', and 'attr' (default is all off).
+
+ - --fix
+
+   This is an EXPERIMENTAL feature.  If correctable errors exists, a file
+   <inputfile>.EXPERIMENTAL-checkpatch-fixes is created which has the
+   automatically fixable errors corrected.
+
+ - --fix-inplace
+
+   EXPERIMENTAL - Similar to --fix but input file is overwritten with fixes.
+
+   DO NOT USE this flag unless you are absolutely sure and you have a backup
+   in place.
+
+ - --ignore-perl-version
+
+   Override checking of perl version.  Runtime errors maybe encountered after
+   enabling this flag if the perl version does not meet the minimum specified.
+
+ - --codespell
+
+   Use the codespell dictionary for checking spelling errors.
+
+ - --codespellfile
+
+   Use the specified codespell file.
+   Default is '/usr/share/codespell/dictionary.txt'.
+
+ - --typedefsfile
+
+   Read additional types from this file.
+
+ - --color[=WHEN]
+
+   Use colors 'always', 'never', or only when output is a terminal ('auto').
+   Default is 'auto'.
+
+ - --kconfig-prefix=WORD
+
+   Use WORD as a prefix for Kconfig symbols (default is `CONFIG_`).
+
+ - -h, --help, --version
+
+   Display the help text.
+
+Message Levels
+==============
+
+Messages in checkpatch are divided into three levels. The levels of messages
+in checkpatch denote the severity of the error. They are:
+
+ - ERROR
+
+   This is the most strict level.  Messages of type ERROR must be taken
+   seriously as they denote things that are very likely to be wrong.
+
+ - WARNING
+
+   This is the next stricter level.  Messages of type WARNING requires a
+   more careful review.  But it is milder than an ERROR.
+
+ - CHECK
+
+   This is the mildest level.  These are things which may require some thought.
+
+Type Descriptions
+=================
+
+This section contains a description of all the message types in checkpatch.
+
+.. Types in this section are also parsed by checkpatch.
+.. The types are grouped into subsections based on use.
+
+
+Allocation style
+----------------
+
+  **ALLOC_ARRAY_ARGS**
+    The first argument for kcalloc or kmalloc_array should be the
+    number of elements.  sizeof() as the first argument is generally
+    wrong.
+
+    See: https://www.kernel.org/doc/html/latest/core-api/memory-allocation.html
+
+  **ALLOC_SIZEOF_STRUCT**
+    The allocation style is bad.  In general for family of
+    allocation functions using sizeof() to get memory size,
+    constructs like::
+
+      p = alloc(sizeof(struct foo), ...)
+
+    should be::
+
+      p = alloc(sizeof(*p), ...)
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#allocating-memory
+
+  **ALLOC_WITH_MULTIPLY**
+    Prefer kmalloc_array/kcalloc over kmalloc/kzalloc with a
+    sizeof multiply.
+
+    See: https://www.kernel.org/doc/html/latest/core-api/memory-allocation.html
+
+
+API usage
+---------
+
+  **ARCH_DEFINES**
+    Architecture specific defines should be avoided wherever
+    possible.
+
+  **ARCH_INCLUDE_LINUX**
+    Whenever asm/file.h is included and linux/file.h exists, a
+    conversion can be made when linux/file.h includes asm/file.h.
+    However this is not always the case (See signal.h).
+    This message type is emitted only for includes from arch/.
+
+  **AVOID_BUG**
+    BUG() or BUG_ON() should be avoided totally.
+    Use WARN() and WARN_ON() instead, and handle the "impossible"
+    error condition as gracefully as possible.
+
+    See: https://www.kernel.org/doc/html/latest/process/deprecated.html#bug-and-bug-on
+
+  **CONSIDER_KSTRTO**
+    The simple_strtol(), simple_strtoll(), simple_strtoul(), and
+    simple_strtoull() functions explicitly ignore overflows, which
+    may lead to unexpected results in callers.  The respective kstrtol(),
+    kstrtoll(), kstrtoul(), and kstrtoull() functions tend to be the
+    correct replacements.
+
+    See: https://www.kernel.org/doc/html/latest/process/deprecated.html#simple-strtol-simple-strtoll-simple-strtoul-simple-strtoull
+
+  **CONSTANT_CONVERSION**
+    Use of __constant_<foo> form is discouraged for the following functions::
+
+      __constant_cpu_to_be[x]
+      __constant_cpu_to_le[x]
+      __constant_be[x]_to_cpu
+      __constant_le[x]_to_cpu
+      __constant_htons
+      __constant_ntohs
+
+    Using any of these outside of include/uapi/ is not preferred as using the
+    function without __constant_ is identical when the argument is a
+    constant.
+
+    In big endian systems, the macros like __constant_cpu_to_be32(x) and
+    cpu_to_be32(x) expand to the same expression::
+
+      #define __constant_cpu_to_be32(x) ((__force __be32)(__u32)(x))
+      #define __cpu_to_be32(x)          ((__force __be32)(__u32)(x))
+
+    In little endian systems, the macros __constant_cpu_to_be32(x) and
+    cpu_to_be32(x) expand to __constant_swab32 and __swab32.  __swab32
+    has a __builtin_constant_p check::
+
+      #define __swab32(x)				\
+        (__builtin_constant_p((__u32)(x)) ?	\
+        ___constant_swab32(x) :			\
+        __fswab32(x))
+
+    So ultimately they have a special case for constants.
+    Similar is the case with all of the macros in the list.  Thus
+    using the __constant_... forms are unnecessarily verbose and
+    not preferred outside of include/uapi.
+
+    See: https://lore.kernel.org/lkml/1400106425.12666.6.camel@joe-AO725/
+
+  **DEPRECATED_API**
+    Usage of a deprecated RCU API is detected.  It is recommended to replace
+    old flavourful RCU APIs by their new vanilla-RCU counterparts.
+
+    The full list of available RCU APIs can be viewed from the kernel docs.
+
+    See: https://www.kernel.org/doc/html/latest/RCU/whatisRCU.html#full-list-of-rcu-apis
+
+  **DEPRECATED_VARIABLE**
+    EXTRA_{A,C,CPP,LD}FLAGS are deprecated and should be replaced by the new
+    flags added via commit f77bf01425b1 ("kbuild: introduce ccflags-y,
+    asflags-y and ldflags-y").
+
+    The following conversion scheme maybe used::
+
+      EXTRA_AFLAGS    ->  asflags-y
+      EXTRA_CFLAGS    ->  ccflags-y
+      EXTRA_CPPFLAGS  ->  cppflags-y
+      EXTRA_LDFLAGS   ->  ldflags-y
+
+    See:
+
+      1. https://lore.kernel.org/lkml/20070930191054.GA15876@uranus.ravnborg.org/
+      2. https://lore.kernel.org/lkml/1313384834-24433-12-git-send-email-lacombar@gmail.com/
+      3. https://www.kernel.org/doc/html/latest/kbuild/makefiles.html#compilation-flags
+
+  **DEVICE_ATTR_FUNCTIONS**
+    The function names used in DEVICE_ATTR is unusual.
+    Typically, the store and show functions are used with <attr>_store and
+    <attr>_show, where <attr> is a named attribute variable of the device.
+
+    Consider the following examples::
+
+      static DEVICE_ATTR(type, 0444, type_show, NULL);
+      static DEVICE_ATTR(power, 0644, power_show, power_store);
+
+    The function names should preferably follow the above pattern.
+
+    See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes
+
+  **DEVICE_ATTR_RO**
+    The DEVICE_ATTR_RO(name) helper macro can be used instead of
+    DEVICE_ATTR(name, 0444, name_show, NULL);
+
+    Note that the macro automatically appends _show to the named
+    attribute variable of the device for the show method.
+
+    See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes
+
+  **DEVICE_ATTR_RW**
+    The DEVICE_ATTR_RW(name) helper macro can be used instead of
+    DEVICE_ATTR(name, 0644, name_show, name_store);
+
+    Note that the macro automatically appends _show and _store to the
+    named attribute variable of the device for the show and store methods.
+
+    See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes
+
+  **DEVICE_ATTR_WO**
+    The DEVICE_AATR_WO(name) helper macro can be used instead of
+    DEVICE_ATTR(name, 0200, NULL, name_store);
+
+    Note that the macro automatically appends _store to the
+    named attribute variable of the device for the store method.
+
+    See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes
+
+  **DUPLICATED_SYSCTL_CONST**
+    Commit d91bff3011cf ("proc/sysctl: add shared variables for range
+    check") added some shared const variables to be used instead of a local
+    copy in each source file.
+
+    Consider replacing the sysctl range checking value with the shared
+    one in include/linux/sysctl.h.  The following conversion scheme may
+    be used::
+
+      &zero     ->  SYSCTL_ZERO
+      &one      ->  SYSCTL_ONE
+      &int_max  ->  SYSCTL_INT_MAX
+
+    See:
+
+      1. https://lore.kernel.org/lkml/20190430180111.10688-1-mcroce@redhat.com/
+      2. https://lore.kernel.org/lkml/20190531131422.14970-1-mcroce@redhat.com/
+
+  **ENOSYS**
+    ENOSYS means that a nonexistent system call was called.
+    Earlier, it was wrongly used for things like invalid operations on
+    otherwise valid syscalls.  This should be avoided in new code.
+
+    See: https://lore.kernel.org/lkml/5eb299021dec23c1a48fa7d9f2c8b794e967766d.1408730669.git.luto@amacapital.net/
+
+  **ENOTSUPP**
+    ENOTSUPP is not a standard error code and should be avoided in new patches.
+    EOPNOTSUPP should be used instead.
+
+    See: https://lore.kernel.org/netdev/20200510182252.GA411829@lunn.ch/
+
+  **EXPORT_SYMBOL**
+    EXPORT_SYMBOL should immediately follow the symbol to be exported.
+
+  **IN_ATOMIC**
+    in_atomic() is not for driver use so any such use is reported as an ERROR.
+    Also in_atomic() is often used to determine if sleeping is permitted,
+    but it is not reliable in this use model.  Therefore its use is
+    strongly discouraged.
+
+    However, in_atomic() is ok for core kernel use.
+
+    See: https://lore.kernel.org/lkml/20080320201723.b87b3732.akpm@linux-foundation.org/
+
+  **LOCKDEP**
+    The lockdep_no_validate class was added as a temporary measure to
+    prevent warnings on conversion of device->sem to device->mutex.
+    It should not be used for any other purpose.
+
+    See: https://lore.kernel.org/lkml/1268959062.9440.467.camel@laptop/
+
+  **MALFORMED_INCLUDE**
+    The #include statement has a malformed path.  This has happened
+    because the author has included a double slash "//" in the pathname
+    accidentally.
+
+  **USE_LOCKDEP**
+    lockdep_assert_held() annotations should be preferred over
+    assertions based on spin_is_locked()
+
+    See: https://www.kernel.org/doc/html/latest/locking/lockdep-design.html#annotations
+
+  **UAPI_INCLUDE**
+    No #include statements in include/uapi should use a uapi/ path.
+
+  **USLEEP_RANGE**
+    usleep_range() should be preferred over udelay(). The proper way of
+    using usleep_range() is mentioned in the kernel docs.
+
+    See: https://www.kernel.org/doc/html/latest/timers/timers-howto.html#delays-information-on-the-various-kernel-delay-sleep-mechanisms
+
+
+Comments
+--------
+
+  **BLOCK_COMMENT_STYLE**
+    The comment style is incorrect.  The preferred style for multi-
+    line comments is::
+
+      /*
+      * This is the preferred style
+      * for multi line comments.
+      */
+
+    The networking comment style is a bit different, with the first line
+    not empty like the former::
+
+      /* This is the preferred comment style
+      * for files in net/ and drivers/net/
+      */
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#commenting
+
+  **C99_COMMENTS**
+    C99 style single line comments (//) should not be used.
+    Prefer the block comment style instead.
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#commenting
+
+  **DATA_RACE**
+    Applications of data_race() should have a comment so as to document the
+    reasoning behind why it was deemed safe.
+
+    See: https://lore.kernel.org/lkml/20200401101714.44781-1-elver@google.com/
+
+  **FSF_MAILING_ADDRESS**
+    Kernel maintainers reject new instances of the GPL boilerplate paragraph
+    directing people to write to the FSF for a copy of the GPL, since the
+    FSF has moved in the past and may do so again.
+    So do not write paragraphs about writing to the Free Software Foundation's
+    mailing address.
+
+    See: https://lore.kernel.org/lkml/20131006222342.GT19510@leaf/
+
+
+Commit message
+--------------
+
+  **BAD_SIGN_OFF**
+    The signed-off-by line does not fall in line with the standards
+    specified by the community.
+
+    See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#developer-s-certificate-of-origin-1-1
+
+  **BAD_STABLE_ADDRESS_STYLE**
+    The email format for stable is incorrect.
+    Some valid options for stable address are::
+
+      1. stable@vger.kernel.org
+      2. stable@kernel.org
+
+    For adding version info, the following comment style should be used::
+
+      stable@vger.kernel.org # version info
+
+  **COMMIT_COMMENT_SYMBOL**
+    Commit log lines starting with a '#' are ignored by git as
+    comments.  To solve this problem addition of a single space
+    infront of the log line is enough.
+
+  **COMMIT_MESSAGE**
+    The patch is missing a commit description.  A brief
+    description of the changes made by the patch should be added.
+
+    See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes
+
+  **EMAIL_SUBJECT**
+    Naming the tool that found the issue is not very useful in the
+    subject line.  A good subject line summarizes the change that
+    the patch brings.
+
+    See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes
+
+  **FROM_SIGN_OFF_MISMATCH**
+    The author's email does not match with that in the Signed-off-by:
+    line(s). This can be sometimes caused due to an improperly configured
+    email client.
+
+    This message is emitted due to any of the following reasons::
+
+      - The email names do not match.
+      - The email addresses do not match.
+      - The email subaddresses do not match.
+      - The email comments do not match.
+
+  **MISSING_SIGN_OFF**
+    The patch is missing a Signed-off-by line.  A signed-off-by
+    line should be added according to Developer's certificate of
+    Origin.
+
+    See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin
+
+  **NO_AUTHOR_SIGN_OFF**
+    The author of the patch has not signed off the patch.  It is
+    required that a simple sign off line should be present at the
+    end of explanation of the patch to denote that the author has
+    written it or otherwise has the rights to pass it on as an open
+    source patch.
+
+    See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin
+
+  **DIFF_IN_COMMIT_MSG**
+    Avoid having diff content in commit message.
+    This causes problems when one tries to apply a file containing both
+    the changelog and the diff because patch(1) tries to apply the diff
+    which it found in the changelog.
+
+    See: https://lore.kernel.org/lkml/20150611134006.9df79a893e3636019ad2759e@linux-foundation.org/
+
+  **GERRIT_CHANGE_ID**
+    To be picked up by gerrit, the footer of the commit message might
+    have a Change-Id like::
+
+      Change-Id: Ic8aaa0728a43936cd4c6e1ed590e01ba8f0fbf5b
+      Signed-off-by: A. U. Thor <author@example.com>
+
+    The Change-Id line must be removed before submitting.
+
+  **GIT_COMMIT_ID**
+    The proper way to reference a commit id is:
+    commit <12+ chars of sha1> ("<title line>")
+
+    An example may be::
+
+      Commit e21d2170f36602ae2708 ("video: remove unnecessary
+      platform_set_drvdata()") removed the unnecessary
+      platform_set_drvdata(), but left the variable "dev" unused,
+      delete it.
+
+    See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes
+
+
+Comparison style
+----------------
+
+  **ASSIGN_IN_IF**
+    Do not use assignments in if condition.
+    Example::
+
+      if ((foo = bar(...)) < BAZ) {
+
+    should be written as::
+
+      foo = bar(...);
+      if (foo < BAZ) {
+
+  **BOOL_COMPARISON**
+    Comparisons of A to true and false are better written
+    as A and !A.
+
+    See: https://lore.kernel.org/lkml/1365563834.27174.12.camel@joe-AO722/
+
+  **COMPARISON_TO_NULL**
+    Comparisons to NULL in the form (foo == NULL) or (foo != NULL)
+    are better written as (!foo) and (foo).
+
+  **CONSTANT_COMPARISON**
+    Comparisons with a constant or upper case identifier on the left
+    side of the test should be avoided.
+
+
+Indentation and Line Breaks
+---------------------------
+
+  **CODE_INDENT**
+    Code indent should use tabs instead of spaces.
+    Outside of comments, documentation and Kconfig,
+    spaces are never used for indentation.
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation
+
+  **DEEP_INDENTATION**
+    Indentation with 6 or more tabs usually indicate overly indented
+    code.
+
+    It is suggested to refactor excessive indentation of
+    if/else/for/do/while/switch statements.
+
+    See: https://lore.kernel.org/lkml/1328311239.21255.24.camel@joe2Laptop/
+
+  **SWITCH_CASE_INDENT_LEVEL**
+    switch should be at the same indent as case.
+    Example::
+
+      switch (suffix) {
+      case 'G':
+      case 'g':
+              mem <<= 30;
+              break;
+      case 'M':
+      case 'm':
+              mem <<= 20;
+              break;
+      case 'K':
+      case 'k':
+              mem <<= 10;
+              fallthrough;
+      default:
+              break;
+      }
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation
+
+  **LONG_LINE**
+    The line has exceeded the specified maximum length.
+    To use a different maximum line length, the --max-line-length=n option
+    may be added while invoking checkpatch.
+
+    Earlier, the default line length was 80 columns.  Commit bdc48fa11e46
+    ("checkpatch/coding-style: deprecate 80-column warning") increased the
+    limit to 100 columns.  This is not a hard limit either and it's
+    preferable to stay within 80 columns whenever possible.
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#breaking-long-lines-and-strings
+
+  **LONG_LINE_STRING**
+    A string starts before but extends beyond the maximum line length.
+    To use a different maximum line length, the --max-line-length=n option
+    may be added while invoking checkpatch.
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#breaking-long-lines-and-strings
+
+  **LONG_LINE_COMMENT**
+    A comment starts before but extends beyond the maximum line length.
+    To use a different maximum line length, the --max-line-length=n option
+    may be added while invoking checkpatch.
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#breaking-long-lines-and-strings
+
+  **SPLIT_STRING**
+    Quoted strings that appear as messages in userspace and can be
+    grepped, should not be split across multiple lines.
+
+    See: https://lore.kernel.org/lkml/20120203052727.GA15035@leaf/
+
+  **MULTILINE_DEREFERENCE**
+    A single dereferencing identifier spanned on multiple lines like::
+
+      struct_identifier->member[index].
+      member = <foo>;
+
+    is generally hard to follow. It can easily lead to typos and so makes
+    the code vulnerable to bugs.
+
+    If fixing the multiple line dereferencing leads to an 80 column
+    violation, then either rewrite the code in a more simple way or if the
+    starting part of the dereferencing identifier is the same and used at
+    multiple places then store it in a temporary variable, and use that
+    temporary variable only at all the places. For example, if there are
+    two dereferencing identifiers::
+
+      member1->member2->member3.foo1;
+      member1->member2->member3.foo2;
+
+    then store the member1->member2->member3 part in a temporary variable.
+    It not only helps to avoid the 80 column violation but also reduces
+    the program size by removing the unnecessary dereferences.
+
+    But if none of the above methods work then ignore the 80 column
+    violation because it is much easier to read a dereferencing identifier
+    on a single line.
+
+  **TRAILING_STATEMENTS**
+    Trailing statements (for example after any conditional) should be
+    on the next line.
+    Statements, such as::
+
+      if (x == y) break;
+
+    should be::
+
+      if (x == y)
+              break;
+
+
+Macros, Attributes and Symbols
+------------------------------
+
+  **ARRAY_SIZE**
+    The ARRAY_SIZE(foo) macro should be preferred over
+    sizeof(foo)/sizeof(foo[0]) for finding number of elements in an
+    array.
+
+    The macro is defined in include/linux/kernel.h::
+
+      #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+
+  **AVOID_EXTERNS**
+    Function prototypes don't need to be declared extern in .h
+    files.  It's assumed by the compiler and is unnecessary.
+
+  **AVOID_L_PREFIX**
+    Local symbol names that are prefixed with `.L` should be avoided,
+    as this has special meaning for the assembler; a symbol entry will
+    not be emitted into the symbol table.  This can prevent `objtool`
+    from generating correct unwind info.
+
+    Symbols with STB_LOCAL binding may still be used, and `.L` prefixed
+    local symbol names are still generally usable within a function,
+    but `.L` prefixed local symbol names should not be used to denote
+    the beginning or end of code regions via
+    `SYM_CODE_START_LOCAL`/`SYM_CODE_END`
+
+  **BIT_MACRO**
+    Defines like: 1 << <digit> could be BIT(digit).
+    The BIT() macro is defined via include/linux/bits.h::
+
+      #define BIT(nr)         (1UL << (nr))
+
+  **CONST_READ_MOSTLY**
+    When a variable is tagged with the __read_mostly annotation, it is a
+    signal to the compiler that accesses to the variable will be mostly
+    reads and rarely(but NOT never) a write.
+
+    const __read_mostly does not make any sense as const data is already
+    read-only.  The __read_mostly annotation thus should be removed.
+
+  **DATE_TIME**
+    It is generally desirable that building the same source code with
+    the same set of tools is reproducible, i.e. the output is always
+    exactly the same.
+
+    The kernel does *not* use the ``__DATE__`` and ``__TIME__`` macros,
+    and enables warnings if they are used as they can lead to
+    non-deterministic builds.
+
+    See: https://www.kernel.org/doc/html/latest/kbuild/reproducible-builds.html#timestamps
+
+  **DEFINE_ARCH_HAS**
+    The ARCH_HAS_xyz and ARCH_HAVE_xyz patterns are wrong.
+
+    For big conceptual features use Kconfig symbols instead.  And for
+    smaller things where we have compatibility fallback functions but
+    want architectures able to override them with optimized ones, we
+    should either use weak functions (appropriate for some cases), or
+    the symbol that protects them should be the same symbol we use.
+
+    See: https://lore.kernel.org/lkml/CA+55aFycQ9XJvEOsiM3txHL5bjUc8CeKWJNR_H+MiicaddB42Q@mail.gmail.com/
+
+  **DO_WHILE_MACRO_WITH_TRAILING_SEMICOLON**
+    do {} while(0) macros should not have a trailing semicolon.
+
+  **INIT_ATTRIBUTE**
+    Const init definitions should use __initconst instead of
+    __initdata.
+
+    Similarly init definitions without const require a separate
+    use of const.
+
+  **INLINE_LOCATION**
+    The inline keyword should sit between storage class and type.
+
+    For example, the following segment::
+
+      inline static int example_function(void)
+      {
+              ...
+      }
+
+    should be::
+
+      static inline int example_function(void)
+      {
+              ...
+      }
+
+  **MISPLACED_INIT**
+    It is possible to use section markers on variables in a way
+    which gcc doesn't understand (or at least not the way the
+    developer intended)::
+
+      static struct __initdata samsung_pll_clock exynos4_plls[nr_plls] = {
+
+    does not put exynos4_plls in the .initdata section. The __initdata
+    marker can be virtually anywhere on the line, except right after
+    "struct". The preferred location is before the "=" sign if there is
+    one, or before the trailing ";" otherwise.
+
+    See: https://lore.kernel.org/lkml/1377655732.3619.19.camel@joe-AO722/
+
+  **MULTISTATEMENT_MACRO_USE_DO_WHILE**
+    Macros with multiple statements should be enclosed in a
+    do - while block.  Same should also be the case for macros
+    starting with `if` to avoid logic defects::
+
+      #define macrofun(a, b, c)                 \
+        do {                                    \
+                if (a == 5)                     \
+                        do_this(b, c);          \
+        } while (0)
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#macros-enums-and-rtl
+
+  **PREFER_FALLTHROUGH**
+    Use the `fallthrough;` pseudo keyword instead of
+    `/* fallthrough */` like comments.
+
+  **TRAILING_SEMICOLON**
+    Macro definition should not end with a semicolon. The macro
+    invocation style should be consistent with function calls.
+    This can prevent any unexpected code paths::
+
+      #define MAC do_something;
+
+    If this macro is used within a if else statement, like::
+
+      if (some_condition)
+              MAC;
+
+      else
+              do_something;
+
+    Then there would be a compilation error, because when the macro is
+    expanded there are two trailing semicolons, so the else branch gets
+    orphaned.
+
+    See: https://lore.kernel.org/lkml/1399671106.2912.21.camel@joe-AO725/
+
+  **SINGLE_STATEMENT_DO_WHILE_MACRO**
+    For the multi-statement macros, it is necessary to use the do-while
+    loop to avoid unpredictable code paths. The do-while loop helps to
+    group the multiple statements into a single one so that a
+    function-like macro can be used as a function only.
+
+    But for the single statement macros, it is unnecessary to use the
+    do-while loop. Although the code is syntactically correct but using
+    the do-while loop is redundant. So remove the do-while loop for single
+    statement macros.
+
+  **WEAK_DECLARATION**
+    Using weak declarations like __attribute__((weak)) or __weak
+    can have unintended link defects.  Avoid using them.
+
+
+Functions and Variables
+-----------------------
+
+  **CAMELCASE**
+    Avoid CamelCase Identifiers.
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#naming
+
+  **CONST_CONST**
+    Using `const <type> const *` is generally meant to be
+    written `const <type> * const`.
+
+  **CONST_STRUCT**
+    Using const is generally a good idea.  Checkpatch reads
+    a list of frequently used structs that are always or
+    almost always constant.
+
+    The existing structs list can be viewed from
+    `scripts/const_structs.checkpatch`.
+
+    See: https://lore.kernel.org/lkml/alpine.DEB.2.10.1608281509480.3321@hadrien/
+
+  **EMBEDDED_FUNCTION_NAME**
+    Embedded function names are less appropriate to use as
+    refactoring can cause function renaming.  Prefer the use of
+    "%s", __func__ to embedded function names.
+
+    Note that this does not work with -f (--file) checkpatch option
+    as it depends on patch context providing the function name.
+
+  **FUNCTION_ARGUMENTS**
+    This warning is emitted due to any of the following reasons:
+
+      1. Arguments for the function declaration do not follow
+         the identifier name.  Example::
+
+           void foo
+           (int bar, int baz)
+
+         This should be corrected to::
+
+           void foo(int bar, int baz)
+
+      2. Some arguments for the function definition do not
+         have an identifier name.  Example::
+
+           void foo(int)
+
+         All arguments should have identifier names.
+
+  **FUNCTION_WITHOUT_ARGS**
+    Function declarations without arguments like::
+
+      int foo()
+
+    should be::
+
+      int foo(void)
+
+  **GLOBAL_INITIALISERS**
+    Global variables should not be initialized explicitly to
+    0 (or NULL, false, etc.).  Your compiler (or rather your
+    loader, which is responsible for zeroing out the relevant
+    sections) automatically does it for you.
+
+  **INITIALISED_STATIC**
+    Static variables should not be initialized explicitly to zero.
+    Your compiler (or rather your loader) automatically does
+    it for you.
+
+  **MULTIPLE_ASSIGNMENTS**
+    Multiple assignments on a single line makes the code unnecessarily
+    complicated. So on a single line assign value to a single variable
+    only, this makes the code more readable and helps avoid typos.
+
+  **RETURN_PARENTHESES**
+    return is not a function and as such doesn't need parentheses::
+
+      return (bar);
+
+    can simply be::
+
+      return bar;
+
+
+Permissions
+-----------
+
+  **DEVICE_ATTR_PERMS**
+    The permissions used in DEVICE_ATTR are unusual.
+    Typically only three permissions are used - 0644 (RW), 0444 (RO)
+    and 0200 (WO).
+
+    See: https://www.kernel.org/doc/html/latest/filesystems/sysfs.html#attributes
+
+  **EXECUTE_PERMISSIONS**
+    There is no reason for source files to be executable.  The executable
+    bit can be removed safely.
+
+  **EXPORTED_WORLD_WRITABLE**
+    Exporting world writable sysfs/debugfs files is usually a bad thing.
+    When done arbitrarily they can introduce serious security bugs.
+    In the past, some of the debugfs vulnerabilities would seemingly allow
+    any local user to write arbitrary values into device registers - a
+    situation from which little good can be expected to emerge.
+
+    See: https://lore.kernel.org/linux-arm-kernel/cover.1296818921.git.segoon@openwall.com/
+
+  **NON_OCTAL_PERMISSIONS**
+    Permission bits should use 4 digit octal permissions (like 0700 or 0444).
+    Avoid using any other base like decimal.
+
+  **SYMBOLIC_PERMS**
+    Permission bits in the octal form are more readable and easier to
+    understand than their symbolic counterparts because many command-line
+    tools use this notation. Experienced kernel developers have been using
+    these traditional Unix permission bits for decades and so they find it
+    easier to understand the octal notation than the symbolic macros.
+    For example, it is harder to read S_IWUSR|S_IRUGO than 0644, which
+    obscures the developer's intent rather than clarifying it.
+
+    See: https://lore.kernel.org/lkml/CA+55aFw5v23T-zvDZp-MmD_EYxF8WbafwwB59934FV7g21uMGQ@mail.gmail.com/
+
+
+Spacing and Brackets
+--------------------
+
+  **ASSIGNMENT_CONTINUATIONS**
+    Assignment operators should not be written at the start of a
+    line but should follow the operand at the previous line.
+
+  **BRACES**
+    The placement of braces is stylistically incorrect.
+    The preferred way is to put the opening brace last on the line,
+    and put the closing brace first::
+
+      if (x is true) {
+              we do y
+      }
+
+    This applies for all non-functional blocks.
+    However, there is one special case, namely functions: they have the
+    opening brace at the beginning of the next line, thus::
+
+      int function(int x)
+      {
+              body of function
+      }
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces
+
+  **BRACKET_SPACE**
+    Whitespace before opening bracket '[' is prohibited.
+    There are some exceptions:
+
+    1. With a type on the left::
+
+        int [] a;
+
+    2. At the beginning of a line for slice initialisers::
+
+        [0...10] = 5,
+
+    3. Inside a curly brace::
+
+        = { [0...10] = 5 }
+
+  **CONCATENATED_STRING**
+    Concatenated elements should have a space in between.
+    Example::
+
+      printk(KERN_INFO"bar");
+
+    should be::
+
+      printk(KERN_INFO "bar");
+
+  **ELSE_AFTER_BRACE**
+    `else {` should follow the closing block `}` on the same line.
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces
+
+  **LINE_SPACING**
+    Vertical space is wasted given the limited number of lines an
+    editor window can display when multiple blank lines are used.
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces
+
+  **OPEN_BRACE**
+    The opening brace should be following the function definitions on the
+    next line.  For any non-functional block it should be on the same line
+    as the last construct.
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces
+
+  **POINTER_LOCATION**
+    When using pointer data or a function that returns a pointer type,
+    the preferred use of * is adjacent to the data name or function name
+    and not adjacent to the type name.
+    Examples::
+
+      char *linux_banner;
+      unsigned long long memparse(char *ptr, char **retptr);
+      char *match_strdup(substring_t *s);
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces
+
+  **SPACING**
+    Whitespace style used in the kernel sources is described in kernel docs.
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces
+
+  **TRAILING_WHITESPACE**
+    Trailing whitespace should always be removed.
+    Some editors highlight the trailing whitespace and cause visual
+    distractions when editing files.
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces
+
+  **UNNECESSARY_PARENTHESES**
+    Parentheses are not required in the following cases:
+
+      1. Function pointer uses::
+
+          (foo->bar)();
+
+        could be::
+
+          foo->bar();
+
+      2. Comparisons in if::
+
+          if ((foo->bar) && (foo->baz))
+          if ((foo == bar))
+
+        could be::
+
+          if (foo->bar && foo->baz)
+          if (foo == bar)
+
+      3. addressof/dereference single Lvalues::
+
+          &(foo->bar)
+          *(foo->bar)
+
+        could be::
+
+          &foo->bar
+          *foo->bar
+
+  **WHILE_AFTER_BRACE**
+    while should follow the closing bracket on the same line::
+
+      do {
+              ...
+      } while(something);
+
+    See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces
+
+
+Others
+------
+
+  **CONFIG_DESCRIPTION**
+    Kconfig symbols should have a help text which fully describes
+    it.
+
+  **CORRUPTED_PATCH**
+    The patch seems to be corrupted or lines are wrapped.
+    Please regenerate the patch file before sending it to the maintainer.
+
+  **CVS_KEYWORD**
+    Since linux moved to git, the CVS markers are no longer used.
+    So, CVS style keywords ($Id$, $Revision$, $Log$) should not be
+    added.
+
+  **DEFAULT_NO_BREAK**
+    switch default case is sometimes written as "default:;".  This can
+    cause new cases added below default to be defective.
+
+    A "break;" should be added after empty default statement to avoid
+    unwanted fallthrough.
+
+  **DOS_LINE_ENDINGS**
+    For DOS-formatted patches, there are extra ^M symbols at the end of
+    the line.  These should be removed.
+
+  **DT_SCHEMA_BINDING_PATCH**
+    DT bindings moved to a json-schema based format instead of
+    freeform text.
+
+    See: https://www.kernel.org/doc/html/latest/devicetree/bindings/writing-schema.html
+
+  **DT_SPLIT_BINDING_PATCH**
+    Devicetree bindings should be their own patch.  This is because
+    bindings are logically independent from a driver implementation,
+    they have a different maintainer (even though they often
+    are applied via the same tree), and it makes for a cleaner history in the
+    DT only tree created with git-filter-branch.
+
+    See: https://www.kernel.org/doc/html/latest/devicetree/bindings/submitting-patches.html#i-for-patch-submitters
+
+  **EMBEDDED_FILENAME**
+    Embedding the complete filename path inside the file isn't particularly
+    useful as often the path is moved around and becomes incorrect.
+
+  **FILE_PATH_CHANGES**
+    Whenever files are added, moved, or deleted, the MAINTAINERS file
+    patterns can be out of sync or outdated.
+
+    So MAINTAINERS might need updating in these cases.
+
+  **MEMSET**
+    The memset use appears to be incorrect.  This may be caused due to
+    badly ordered parameters.  Please recheck the usage.
+
+  **NOT_UNIFIED_DIFF**
+    The patch file does not appear to be in unified-diff format.  Please
+    regenerate the patch file before sending it to the maintainer.
+
+  **PRINTF_0XDECIMAL**
+    Prefixing 0x with decimal output is defective and should be corrected.
+
+  **SPDX_LICENSE_TAG**
+    The source file is missing or has an improper SPDX identifier tag.
+    The Linux kernel requires the precise SPDX identifier in all source files,
+    and it is thoroughly documented in the kernel docs.
+
+    See: https://www.kernel.org/doc/html/latest/process/license-rules.html
+
+  **TYPO_SPELLING**
+    Some words may have been misspelled.  Consider reviewing them.