doc/develop/checkpatch.rst - platform/external/u-boot - Gitiles

 .. SPDX-License-Identifier: GPL-2.0-only

 ==========
 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

   **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.


 Comment style
 -------------

   **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


 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

   **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.


 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 in include/linux/bitops.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/

   **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)
       {
               ...
       }

   **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

   **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

   **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.

   **RETURN_PARENTHESES**
     return is not a function and as such doesn't need parentheses::

       return (bar);

     can simply be::

       return bar;


 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 }

   **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

   **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

   **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;
               /* fall through */
       default:
               break;
       }

     See: https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation

   **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

   **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.

   **DOS_LINE_ENDINGS**
     For DOS-formatted patches, there are extra ^M symbols at the end of
     the line.  These should be removed.

   **EXECUTE_PERMISSIONS**
     There is no reason for source files to be executable.  The executable
     bit can be removed safely.

   **NON_OCTAL_PERMISSIONS**
     Permission bits should use 4 digit octal permissions (like 0700 or 0444).
     Avoid using any other base like decimal.

   **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.

   **TRAILING_STATEMENTS**
     Trailing statements (for example after any conditional) should be
     on the next line.
     Like::

       if (x == y) break;

     should be::

       if (x == y)
               break;
	.. SPDX-License-Identifier: GPL-2.0-only

	==========
	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

	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.


	Comment style
	-------------

	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


	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

	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.


	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 in include/linux/bitops.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/

	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)
	{
	...
	}

	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

	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

	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.

	RETURN_PARENTHESES
	return is not a function and as such doesn't need parentheses::

	return (bar);

	can simply be::

	return bar;


	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 }

	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

	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

	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;
	/* fall through */
	default:
	break;
	}

	See: https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation

	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

	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.

	DOS_LINE_ENDINGS
	For DOS-formatted patches, there are extra ^M symbols at the end of
	the line. These should be removed.

	EXECUTE_PERMISSIONS
	There is no reason for source files to be executable. The executable
	bit can be removed safely.

	NON_OCTAL_PERMISSIONS
	Permission bits should use 4 digit octal permissions (like 0700 or 0444).
	Avoid using any other base like decimal.

	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.

	TRAILING_STATEMENTS
	Trailing statements (for example after any conditional) should be
	on the next line.
	Like::

	if (x == y) break;

	should be::

	if (x == y)
	break;