Adding upstream version 4.19.249.upstream/4.19.249

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

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+Writing kernel-doc comments
+===========================
+
+The Linux kernel source files may contain structured documentation
+comments in the kernel-doc format to describe the functions, types
+and design of the code. It is easier to keep documentation up-to-date
+when it is embedded in source files.
+
+.. note:: The kernel-doc format is deceptively similar to javadoc,
+   gtk-doc or Doxygen, yet distinctively different, for historical
+   reasons. The kernel source contains tens of thousands of kernel-doc
+   comments. Please stick to the style described here.
+
+The kernel-doc structure is extracted from the comments, and proper
+`Sphinx C Domain`_ function and type descriptions with anchors are
+generated from them. The descriptions are filtered for special kernel-doc
+highlights and cross-references. See below for details.
+
+.. _Sphinx C Domain: http://www.sphinx-doc.org/en/stable/domains.html
+
+Every function that is exported to loadable modules using
+``EXPORT_SYMBOL`` or ``EXPORT_SYMBOL_GPL`` should have a kernel-doc
+comment. Functions and data structures in header files which are intended
+to be used by modules should also have kernel-doc comments.
+
+It is good practice to also provide kernel-doc formatted documentation
+for functions externally visible to other kernel files (not marked
+``static``). We also recommend providing kernel-doc formatted
+documentation for private (file ``static``) routines, for consistency of
+kernel source code layout. This is lower priority and at the discretion
+of the maintainer of that kernel source file.
+
+How to format kernel-doc comments
+---------------------------------
+
+The opening comment mark ``/**`` is used for kernel-doc comments. The
+``kernel-doc`` tool will extract comments marked this way. The rest of
+the comment is formatted like a normal multi-line comment with a column
+of asterisks on the left side, closing with ``*/`` on a line by itself.
+
+The function and type kernel-doc comments should be placed just before
+the function or type being described in order to maximise the chance
+that somebody changing the code will also change the documentation. The
+overview kernel-doc comments may be placed anywhere at the top indentation
+level.
+
+Running the ``kernel-doc`` tool with increased verbosity and without actual
+output generation may be used to verify proper formatting of the
+documentation comments. For example::
+
+	scripts/kernel-doc -v -none drivers/foo/bar.c
+
+The documentation format is verified by the kernel build when it is
+requested to perform extra gcc checks::
+
+	make W=n
+
+Function documentation
+----------------------
+
+The general format of a function and function-like macro kernel-doc comment is::
+
+  /**
+   * function_name() - Brief description of function.
+   * @arg1: Describe the first argument.
+   * @arg2: Describe the second argument.
+   *        One can provide multiple line descriptions
+   *        for arguments.
+   *
+   * A longer description, with more discussion of the function function_name()
+   * that might be useful to those using or modifying it. Begins with an
+   * empty comment line, and may include additional embedded empty
+   * comment lines.
+   *
+   * The longer description may have multiple paragraphs.
+   *
+   * Context: Describes whether the function can sleep, what locks it takes,
+   *          releases, or expects to be held. It can extend over multiple
+   *          lines.
+   * Return: Describe the return value of foobar.
+   *
+   * The return value description can also have multiple paragraphs, and should
+   * be placed at the end of the comment block.
+   */
+
+The brief description following the function name may span multiple lines, and
+ends with an argument description, a blank comment line, or the end of the
+comment block.
+
+Function parameters
+~~~~~~~~~~~~~~~~~~~
+
+Each function argument should be described in order, immediately following
+the short function description.  Do not leave a blank line between the
+function description and the arguments, nor between the arguments.
+
+Each ``@argument:`` description may span multiple lines.
+
+.. note::
+
+   If the ``@argument`` description has multiple lines, the continuation
+   of the description should start at the same column as the previous line::
+
+      * @argument: some long description
+      *            that continues on next lines
+
+   or::
+
+      * @argument:
+      *		some long description
+      *		that continues on next lines
+
+If a function has a variable number of arguments, its description should
+be written in kernel-doc notation as::
+
+      * @...: description
+
+Function context
+~~~~~~~~~~~~~~~~
+
+The context in which a function can be called should be described in a
+section named ``Context``. This should include whether the function
+sleeps or can be called from interrupt context, as well as what locks
+it takes, releases and expects to be held by its caller.
+
+Examples::
+
+  * Context: Any context.
+  * Context: Any context. Takes and releases the RCU lock.
+  * Context: Any context. Expects <lock> to be held by caller.
+  * Context: Process context. May sleep if @gfp flags permit.
+  * Context: Process context. Takes and releases <mutex>.
+  * Context: Softirq or process context. Takes and releases <lock>, BH-safe.
+  * Context: Interrupt context.
+
+Return values
+~~~~~~~~~~~~~
+
+The return value, if any, should be described in a dedicated section
+named ``Return``.
+
+.. note::
+
+  #) The multi-line descriptive text you provide does *not* recognize
+     line breaks, so if you try to format some text nicely, as in::
+
+	* Return:
+	* 0 - OK
+	* -EINVAL - invalid argument
+	* -ENOMEM - out of memory
+
+     this will all run together and produce::
+
+	Return: 0 - OK -EINVAL - invalid argument -ENOMEM - out of memory
+
+     So, in order to produce the desired line breaks, you need to use a
+     ReST list, e. g.::
+
+      * Return:
+      * * 0		- OK to runtime suspend the device
+      * * -EBUSY	- Device should not be runtime suspended
+
+  #) If the descriptive text you provide has lines that begin with
+     some phrase followed by a colon, each of those phrases will be taken
+     as a new section heading, which probably won't produce the desired
+     effect.
+
+Structure, union, and enumeration documentation
+-----------------------------------------------
+
+The general format of a struct, union, and enum kernel-doc comment is::
+
+  /**
+   * struct struct_name - Brief description.
+   * @member1: Description of member1.
+   * @member2: Description of member2.
+   *           One can provide multiple line descriptions
+   *           for members.
+   *
+   * Description of the structure.
+   */
+
+You can replace the ``struct`` in the above example with ``union`` or
+``enum``  to describe unions or enums. ``member`` is used to mean struct
+and union member names as well as enumerations in an enum.
+
+The brief description following the structure name may span multiple
+lines, and ends with a member description, a blank comment line, or the
+end of the comment block.
+
+Members
+~~~~~~~
+
+Members of structs, unions and enums should be documented the same way
+as function parameters; they immediately succeed the short description
+and may be multi-line.
+
+Inside a struct or union description, you can use the ``private:`` and
+``public:`` comment tags. Structure fields that are inside a ``private:``
+area are not listed in the generated output documentation.
+
+The ``private:`` and ``public:`` tags must begin immediately following a
+``/*`` comment marker. They may optionally include comments between the
+``:`` and the ending ``*/`` marker.
+
+Example::
+
+  /**
+   * struct my_struct - short description
+   * @a: first member
+   * @b: second member
+   * @d: fourth member
+   *
+   * Longer description
+   */
+  struct my_struct {
+      int a;
+      int b;
+  /* private: internal use only */
+      int c;
+  /* public: the next one is public */
+      int d;
+  };
+
+Nested structs/unions
+~~~~~~~~~~~~~~~~~~~~~
+
+It is possible to document nested structs and unions, like::
+
+      /**
+       * struct nested_foobar - a struct with nested unions and structs
+       * @memb1: first member of anonymous union/anonymous struct
+       * @memb2: second member of anonymous union/anonymous struct
+       * @memb3: third member of anonymous union/anonymous struct
+       * @memb4: fourth member of anonymous union/anonymous struct
+       * @bar: non-anonymous union
+       * @bar.st1: struct st1 inside @bar
+       * @bar.st2: struct st2 inside @bar
+       * @bar.st1.memb1: first member of struct st1 on union bar
+       * @bar.st1.memb2: second member of struct st1 on union bar
+       * @bar.st2.memb1: first member of struct st2 on union bar
+       * @bar.st2.memb2: second member of struct st2 on union bar
+       */
+      struct nested_foobar {
+        /* Anonymous union/struct*/
+        union {
+          struct {
+            int memb1;
+            int memb2;
+        }
+          struct {
+            void *memb3;
+            int memb4;
+          }
+        }
+        union {
+          struct {
+            int memb1;
+            int memb2;
+          } st1;
+          struct {
+            void *memb1;
+            int memb2;
+          } st2;
+        } bar;
+      };
+
+.. note::
+
+   #) When documenting nested structs or unions, if the struct/union ``foo``
+      is named, the member ``bar`` inside it should be documented as
+      ``@foo.bar:``
+   #) When the nested struct/union is anonymous, the member ``bar`` in it
+      should be documented as ``@bar:``
+
+In-line member documentation comments
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The structure members may also be documented in-line within the definition.
+There are two styles, single-line comments where both the opening ``/**`` and
+closing ``*/`` are on the same line, and multi-line comments where they are each
+on a line of their own, like all other kernel-doc comments::
+
+  /**
+   * struct foo - Brief description.
+   * @foo: The Foo member.
+   */
+  struct foo {
+        int foo;
+        /**
+         * @bar: The Bar member.
+         */
+        int bar;
+        /**
+         * @baz: The Baz member.
+         *
+         * Here, the member description may contain several paragraphs.
+         */
+        int baz;
+        union {
+                /** @foobar: Single line description. */
+                int foobar;
+        };
+        /** @bar2: Description for struct @bar2 inside @foo */
+        struct {
+                /**
+                 * @bar2.barbar: Description for @barbar inside @foo.bar2
+                 */
+                int barbar;
+        } bar2;
+  };
+
+Typedef documentation
+---------------------
+
+The general format of a typedef kernel-doc comment is::
+
+  /**
+   * typedef type_name - Brief description.
+   *
+   * Description of the type.
+   */
+
+Typedefs with function prototypes can also be documented::
+
+  /**
+   * typedef type_name - Brief description.
+   * @arg1: description of arg1
+   * @arg2: description of arg2
+   *
+   * Description of the type.
+   *
+   * Context: Locking context.
+   * Return: Meaning of the return value.
+   */
+   typedef void (*type_name)(struct v4l2_ctrl *arg1, void *arg2);
+
+Highlights and cross-references
+-------------------------------
+
+The following special patterns are recognized in the kernel-doc comment
+descriptive text and converted to proper reStructuredText markup and `Sphinx C
+Domain`_ references.
+
+.. attention:: The below are **only** recognized within kernel-doc comments,
+	       **not** within normal reStructuredText documents.
+
+``funcname()``
+  Function reference.
+
+``@parameter``
+  Name of a function parameter. (No cross-referencing, just formatting.)
+
+``%CONST``
+  Name of a constant. (No cross-referencing, just formatting.)
+
+````literal````
+  A literal block that should be handled as-is. The output will use a
+  ``monospaced font``.
+
+  Useful if you need to use special characters that would otherwise have some
+  meaning either by kernel-doc script of by reStructuredText.
+
+  This is particularly useful if you need to use things like ``%ph`` inside
+  a function description.
+
+``$ENVVAR``
+  Name of an environment variable. (No cross-referencing, just formatting.)
+
+``&struct name``
+  Structure reference.
+
+``&enum name``
+  Enum reference.
+
+``&typedef name``
+  Typedef reference.
+
+``&struct_name->member`` or ``&struct_name.member``
+  Structure or union member reference. The cross-reference will be to the struct
+  or union definition, not the member directly.
+
+``&name``
+  A generic type reference. Prefer using the full reference described above
+  instead. This is mostly for legacy comments.
+
+Cross-referencing from reStructuredText
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To cross-reference the functions and types defined in the kernel-doc comments
+from reStructuredText documents, please use the `Sphinx C Domain`_
+references. For example::
+
+  See function :c:func:`foo` and struct/union/enum/typedef :c:type:`bar`.
+
+While the type reference works with just the type name, without the
+struct/union/enum/typedef part in front, you may want to use::
+
+  See :c:type:`struct foo <foo>`.
+  See :c:type:`union bar <bar>`.
+  See :c:type:`enum baz <baz>`.
+  See :c:type:`typedef meh <meh>`.
+
+This will produce prettier links, and is in line with how kernel-doc does the
+cross-references.
+
+For further details, please refer to the `Sphinx C Domain`_ documentation.
+
+Overview documentation comments
+-------------------------------
+
+To facilitate having source code and comments close together, you can include
+kernel-doc documentation blocks that are free-form comments instead of being
+kernel-doc for functions, structures, unions, enums, or typedefs. This could be
+used for something like a theory of operation for a driver or library code, for
+example.
+
+This is done by using a ``DOC:`` section keyword with a section title.
+
+The general format of an overview or high-level documentation comment is::
+
+  /**
+   * DOC: Theory of Operation
+   *
+   * The whizbang foobar is a dilly of a gizmo. It can do whatever you
+   * want it to do, at any time. It reads your mind. Here's how it works.
+   *
+   * foo bar splat
+   *
+   * The only drawback to this gizmo is that is can sometimes damage
+   * hardware, software, or its subject(s).
+   */
+
+The title following ``DOC:`` acts as a heading within the source file, but also
+as an identifier for extracting the documentation comment. Thus, the title must
+be unique within the file.
+
+Including kernel-doc comments
+=============================
+
+The documentation comments may be included in any of the reStructuredText
+documents using a dedicated kernel-doc Sphinx directive extension.
+
+The kernel-doc directive is of the format::
+
+  .. kernel-doc:: source
+     :option:
+
+The *source* is the path to a source file, relative to the kernel source
+tree. The following directive options are supported:
+
+export: *[source-pattern ...]*
+  Include documentation for all functions in *source* that have been exported
+  using ``EXPORT_SYMBOL`` or ``EXPORT_SYMBOL_GPL`` either in *source* or in any
+  of the files specified by *source-pattern*.
+
+  The *source-pattern* is useful when the kernel-doc comments have been placed
+  in header files, while ``EXPORT_SYMBOL`` and ``EXPORT_SYMBOL_GPL`` are next to
+  the function definitions.
+
+  Examples::
+
+    .. kernel-doc:: lib/bitmap.c
+       :export:
+
+    .. kernel-doc:: include/net/mac80211.h
+       :export: net/mac80211/*.c
+
+internal: *[source-pattern ...]*
+  Include documentation for all functions and types in *source* that have
+  **not** been exported using ``EXPORT_SYMBOL`` or ``EXPORT_SYMBOL_GPL`` either
+  in *source* or in any of the files specified by *source-pattern*.
+
+  Example::
+
+    .. kernel-doc:: drivers/gpu/drm/i915/intel_audio.c
+       :internal:
+
+doc: *title*
+  Include documentation for the ``DOC:`` paragraph identified by *title* in
+  *source*. Spaces are allowed in *title*; do not quote the *title*. The *title*
+  is only used as an identifier for the paragraph, and is not included in the
+  output. Please make sure to have an appropriate heading in the enclosing
+  reStructuredText document.
+
+  Example::
+
+    .. kernel-doc:: drivers/gpu/drm/i915/intel_audio.c
+       :doc: High Definition Audio over HDMI and Display Port
+
+functions: *[ function ...]*
+  Include documentation for each *function* in *source*.
+  If no *function* if specified, the documentaion for all functions
+  and types in the *source* will be included.
+
+  Examples::
+
+    .. kernel-doc:: lib/bitmap.c
+       :functions: bitmap_parselist bitmap_parselist_user
+
+    .. kernel-doc:: lib/idr.c
+       :functions:
+
+Without options, the kernel-doc directive includes all documentation comments
+from the source file.
+
+The kernel-doc extension is included in the kernel source tree, at
+``Documentation/sphinx/kerneldoc.py``. Internally, it uses the
+``scripts/kernel-doc`` script to extract the documentation comments from the
+source.
+
+.. _kernel_doc:
+
+How to use kernel-doc to generate man pages
+-------------------------------------------
+
+If you just want to use kernel-doc to generate man pages you can do this
+from the kernel git tree::
+
+  $ scripts/kernel-doc -man $(git grep -l '/\*\*' -- :^Documentation :^tools) | scripts/split-man.pl /tmp/man