Date:   Thu, 28 Jan 2021 20:08:01 +0530
From:   Dwaipayan Ray <dwaipayanray1@...il.com>
To:     joe@...ches.com
Cc:     linux-kernel-mentees@...ts.linuxfoundation.org,
        lukas.bulwahn@...il.com, linux-kernel@...r.kernel.org,
        Dwaipayan Ray <dwaipayanray1@...il.com>
Subject: [PATCH v2 2/3] docs: add documentation for checkpatch

Add documentation for kernel script checkpatch.pl.
This documentation is also parsed by checkpatch to
enable a verbose mode.

Only a few test descriptions are added and the rest
will be added later over time to document all the
message types emitted by checkpatch.

Signed-off-by: Dwaipayan Ray <dwaipayanray1@...il.com>
---
 Documentation/dev-tools/checkpatch.rst | 269 +++++++++++++++++++++++++
 1 file changed, 269 insertions(+)
 create mode 100644 Documentation/dev-tools/checkpatch.rst

diff --git a/Documentation/dev-tools/checkpatch.rst b/Documentation/dev-tools/checkpatch.rst
new file mode 100644
index 000000000000..bb23f4dad11e
--- /dev/null
+++ b/Documentation/dev-tools/checkpatch.rst
@@ -0,0 +1,269 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+
+==========
+Checkpatch
+==========
+
+This document describes the kernel script checkpatch.pl.
+
+.. Table of Contents
+
+	=== 1 Introduction
+	=== 2 Options
+	=== 3 Message Levels
+	=== 4 Type Descriptions
+
+1 Introduction
+--------------
+
+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.
+
+It should be noted that checkpatch may not be always right.  At times the human
+judgement should take preference over what checkpatch has to say.  If your code looks
+better with the violations, then its probably best left alone.
+
+
+2 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@...eloper.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,NO_AUTHOR_SIGN_OFF
+
+ - --ignore TYPE(,TYPE2...)
+
+   Strip off messages with the given types.
+
+   Example::
+
+     ./scripts/checkpatch.pl mypatch.patch --ignore EMAIL_SUBJECT,NO_AUTHOR_SIGN_OFF
+
+ - --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).  On exceeding the given length, a 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 min 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 the 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.
+
+3 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.
+
+4 Type Descriptions
+-------------------
+
+This section contains a description of all the message types in checkpatch.
+
+.. Types in this section are also parsed by checkpatch.
+.. Please keep the types sorted alphabetically.
+
+:LINE_SPACING:
+  Vertical space is wasted given the limited number of lines an
+  editor window can display when multiple blank lines are used.
+
+: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.
+  ref: `Documentation/process/submitting-patches.rst`
+
+: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.
+
+:TRAILING_WHITESPACE:
+  Trailing whitespace should always be removed.
+  Some editors highlight the trailing whitespace and cause visual
+  distractions when editing files.
-- 
2.30.0

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