Adding upstream version 2.10.0+dfsg.upstream/2.10.0+dfsgupstream

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

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+Coding Style
+============
+
+The following sections outline the |TF-A| coding style for *C* code. The style
+is based on the `Linux kernel coding style`_, with a few modifications.
+
+The style should not be considered *set in stone*. Feel free to provide feedback
+and suggestions.
+
+.. note::
+   You will almost certainly find code in the |TF-A| repository that does not
+   follow the style. The intent is for all code to do so eventually.
+
+File Encoding
+-------------
+
+The source code must use the **UTF-8** character encoding. Comments and
+documentation may use non-ASCII characters when required (e.g. Greek letters
+used for units) but code itself is still limited to ASCII characters.
+
+Newlines must be in **Unix** style, which means that only the Line Feed (``LF``)
+character is used to break a line and reset to the first column.
+
+Language
+--------
+
+The primary language for comments and naming must be International English. In
+cases where there is a conflict between the American English and British English
+spellings of a word, the American English spelling is used.
+
+Exceptions are made when referring directly to something that does not use
+international style, such as the name of a company. In these cases the existing
+name should be used as-is.
+
+C Language Standard
+-------------------
+
+The C language mode used for TF-A is *GNU99*. This is the "GNU dialect of ISO
+C99", which implies the *ISO C99* standard with GNU extensions.
+
+Both GCC and Clang compiler toolchains have support for *GNU99* mode, though
+Clang does lack support for a small number of GNU extensions. These
+missing extensions are rarely used, however, and should not pose a problem.
+
+.. _misra-compliance:
+
+MISRA Compliance
+----------------
+
+TF-A attempts to comply with the `MISRA C:2012 Guidelines`_. Coverity
+Static Analysis is used to regularly generate a report of current MISRA defects
+and to prevent the addition of new ones.
+
+It is not possible for the project to follow all MISRA guidelines. We maintain
+`a spreadsheet`_ that lists all rules and directives and whether we aim to
+comply with them or not. A rationale is given for each deviation.
+
+.. note::
+   Enforcing a rule does not mean that the codebase is free of defects
+   of that rule, only that they would ideally be removed.
+
+.. note::
+   Third-party libraries are not considered in our MISRA analysis and we do not
+   intend to modify them to make them MISRA compliant.
+
+Indentation
+-----------
+
+Use **tabs** for indentation. The use of spaces for indentation is forbidden
+except in the case where a term is being indented to a boundary that cannot be
+achieved using tabs alone.
+
+Tab spacing should be set to **8 characters**.
+
+Trailing whitespace is not allowed and must be trimmed.
+
+Spacing
+-------
+
+Single spacing should be used around most operators, including:
+
+- Arithmetic operators (``+``, ``-``, ``/``, ``*``)
+- Assignment operators (``=``, ``+=``, etc)
+- Boolean operators (``&&``, ``||``)
+- Comparison operators (``<``, ``>``, ``==``, etc)
+
+A space should also be used to separate parentheses and braces when they are not
+already separated by a newline, such as for the ``if`` statement in the
+following example:
+
+.. code:: c
+
+  int function_foo(bool bar)
+  {
+      if (bar) {
+          function_baz();
+      }
+  }
+
+Note that there is no space between the name of a function and the following
+parentheses.
+
+Control statements (``if``, ``for``, ``switch``, ``while``, etc) must be
+separated from the following open parenthesis by a single space. The previous
+example illustrates this for an ``if`` statement.
+
+Line Length
+-----------
+
+Line length *should* be at most **80 characters**. This limit does not include
+non-printing characters such as the line feed.
+
+This rule is a *should*, not a must, and it is acceptable to exceed the limit
+**slightly** where the readability of the code would otherwise be significantly
+reduced. Use your judgement in these cases.
+
+Blank Lines
+-----------
+
+Functions are usually separated by a single blank line. In certain cases it is
+acceptable to use additional blank lines for clarity, if required.
+
+The file must end with a single newline character. Many editors have the option
+to insert this automatically and to trim multiple blank lines at the end of the
+file.
+
+Braces
+------
+
+Opening Brace Placement
+^^^^^^^^^^^^^^^^^^^^^^^
+
+Braces follow the **Kernighan and Ritchie (K&R)** style, where the opening brace
+is **not** placed on a new line.
+
+Example for a ``while`` loop:
+
+.. code:: c
+
+  while (condition) {
+      foo();
+      bar();
+  }
+
+This style applies to all blocks except for functions which, following the Linux
+style, **do** place the opening brace on a new line.
+
+Example for a function:
+
+.. code:: c
+
+  int my_function(void)
+  {
+      int a;
+
+      a = 1;
+      return a;
+  }
+
+Conditional Statement Bodies
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Where conditional statements (such as ``if``, ``for``, ``while`` and ``do``) are
+used, braces must be placed around the statements that form the body of the
+conditional. This is the case regardless of the number of statements in the
+body.
+
+.. note::
+  This is a notable departure from the Linux coding style that has been
+  adopted to follow MISRA guidelines more closely and to help prevent errors.
+
+For example, use the following style:
+
+.. code:: c
+
+  if (condition) {
+      foo++;
+  }
+
+instead of omitting the optional braces around a single statement:
+
+.. code:: c
+
+  /* This is violating MISRA C 2012: Rule 15.6 */
+  if (condition)
+      foo++;
+
+The reason for this is to prevent accidental changes to control flow when
+modifying the body of the conditional. For example, at a quick glance it is easy
+to think that the value of ``bar`` is only incremented if ``condition``
+evaluates to ``true`` but this is not the case - ``bar`` will always be
+incremented regardless of the condition evaluation. If the developer forgets to
+add braces around the conditional body when adding the ``bar++;`` statement then
+the program execution will not proceed as intended.
+
+.. code:: c
+
+  /* This is violating MISRA C 2012: Rule 15.6 */
+  if (condition)
+      foo++;
+      bar++;
+
+Naming
+------
+
+Functions
+^^^^^^^^^
+
+Use lowercase for function names, separating multiple words with an underscore
+character (``_``). This is sometimes referred to as *Snake Case*. An example is
+given below:
+
+.. code:: c
+
+  void bl2_arch_setup(void)
+  {
+      ...
+  }
+
+Local Variables and Parameters
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Local variables and function parameters use the same format as function names:
+lowercase with underscore separation between multiple words. An example is
+given below:
+
+.. code:: c
+
+  static void set_scr_el3_from_rm(uint32_t type,
+                                  uint32_t interrupt_type_flags,
+                                  uint32_t security_state)
+  {
+      uint32_t flag, bit_pos;
+
+      ...
+
+  }
+
+Preprocessor Macros
+^^^^^^^^^^^^^^^^^^^
+
+Identifiers that are defined using preprocessor macros are written in all
+uppercase text.
+
+.. code:: c
+
+  #define BUFFER_SIZE_BYTES 64
+
+Function Attributes
+-------------------
+
+Place any function attributes after the function type and before the function
+name.
+
+.. code:: c
+
+   void __init plat_arm_interconnect_init(void);
+
+Alignment
+---------
+
+Alignment should be performed primarily with tabs, adding spaces if required to
+achieve a granularity that is smaller than the tab size. For example, with a tab
+size of eight columns it would be necessary to use one tab character and two
+spaces to indent text by ten columns.
+
+Switch Statement Alignment
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+When using ``switch`` statements, align each ``case`` statement with the
+``switch`` so that they are in the same column.
+
+.. code:: c
+
+  switch (condition) {
+  case A:
+      foo();
+  case B:
+      bar();
+  default:
+      baz();
+  }
+
+Pointer Alignment
+^^^^^^^^^^^^^^^^^
+
+The reference and dereference operators (ampersand and *pointer star*) must be
+aligned with the name of the object on which they are operating, as opposed to
+the type of the object.
+
+.. code:: c
+
+  uint8_t *foo;
+
+  foo = &bar;
+
+
+Comments
+--------
+
+The general rule for comments is that the double-slash style of comment (``//``)
+is not allowed. Examples of the allowed comment formats are shown below:
+
+.. code:: c
+
+  /*
+   * This example illustrates the first allowed style for multi-line comments.
+   *
+   * Blank lines within multi-lines are allowed when they add clarity or when
+   * they separate multiple contexts.
+   *
+   */
+
+.. code:: c
+
+  /**************************************************************************
+   * This is the second allowed style for multi-line comments.
+   *
+   * In this style, the first and last lines use asterisks that run the full
+   * width of the comment at its widest point.
+   *
+   * This style can be used for additional emphasis.
+   *
+   *************************************************************************/
+
+.. code:: c
+
+  /* Single line comments can use this format */
+
+.. code:: c
+
+  /***************************************************************************
+   * This alternative single-line comment style can also be used for emphasis.
+   **************************************************************************/
+
+Headers and inclusion
+---------------------
+
+Header guards
+^^^^^^^^^^^^^
+
+For a header file called "some_driver.h" the style used by |TF-A| is:
+
+.. code:: c
+
+  #ifndef SOME_DRIVER_H
+  #define SOME_DRIVER_H
+
+  <header content>
+
+  #endif /* SOME_DRIVER_H */
+
+Include statement ordering
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+All header files that are included by a source file must use the following,
+grouped ordering. This is to improve readability (by making it easier to quickly
+read through the list of headers) and maintainability.
+
+#. *System* includes: Header files from the standard *C* library, such as
+   ``stddef.h`` and ``string.h``.
+
+#. *Project* includes: Header files under the ``include/`` directory within
+   |TF-A| are *project* includes.
+
+#. *Platform* includes: Header files relating to a single, specific platform,
+   and which are located under the ``plat/<platform_name>`` directory within
+   |TF-A|, are *platform* includes.
+
+Within each group, ``#include`` statements must be in alphabetical order,
+taking both the file and directory names into account.
+
+Groups must be separated by a single blank line for clarity.
+
+The example below illustrates the ordering rules using some contrived header
+file names; this type of name reuse should be otherwise avoided.
+
+.. code:: c
+
+  #include <string.h>
+
+  #include <a_dir/example/a_header.h>
+  #include <a_dir/example/b_header.h>
+  #include <a_dir/test/a_header.h>
+  #include <b_dir/example/a_header.h>
+
+  #include "a_header.h"
+
+The preferred approach for third-party headers is to include them immediately
+following system header files like in the example below, where the
+``version.h`` header from the Mbed TLS library immediately follows the
+``stddef.h`` system header.
+
+.. code:: c
+
+  /* system header files */
+  #include <stddef.h>
+
+  /* Mbed TLS header files */
+  #include <mbedtls/version.h>
+
+  /* project header files */
+  #include <drivers/auth/auth_mod.h>
+  #include <drivers/auth/tbbr_cot_common.h>
+
+  /* platform header files */
+  #include <platform_def.h>
+
+
+Include statement variants
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Two variants of the ``#include`` directive are acceptable in the |TF-A|
+codebase. Correct use of the two styles improves readability by suggesting the
+location of the included header and reducing ambiguity in cases where generic
+and platform-specific headers share a name.
+
+For header files that are in the same directory as the source file that is
+including them, use the ``"..."`` variant.
+
+For header files that are **not** in the same directory as the source file that
+is including them, use the ``<...>`` variant.
+
+Example (bl1_fwu.c):
+
+.. code:: c
+
+  #include <assert.h>
+  #include <errno.h>
+  #include <string.h>
+
+  #include "bl1_private.h"
+
+Typedefs
+--------
+
+Avoid anonymous typedefs of structs/enums in headers
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+For example, the following definition:
+
+.. code:: c
+
+  typedef struct {
+          int arg1;
+          int arg2;
+  } my_struct_t;
+
+
+is better written as:
+
+.. code:: c
+
+  struct my_struct {
+          int arg1;
+          int arg2;
+  };
+
+This allows function declarations in other header files that depend on the
+struct/enum to forward declare the struct/enum instead of including the
+entire header:
+
+.. code:: c
+
+  struct my_struct;
+  void my_func(struct my_struct *arg);
+
+instead of:
+
+.. code:: c
+
+  #include <my_struct.h>
+  void my_func(my_struct_t *arg);
+
+Some TF definitions use both a struct/enum name **and** a typedef name. This
+is discouraged for new definitions as it makes it difficult for TF to comply
+with MISRA rule 8.3, which states that "All declarations of an object or
+function shall use the same names and type qualifiers".
+
+The Linux coding standards also discourage new typedefs and checkpatch emits
+a warning for this.
+
+Existing typedefs will be retained for compatibility.
+
+--------------
+
+*Copyright (c) 2020-2023, Arm Limited. All rights reserved.*
+
+.. _`Linux kernel coding style`: https://www.kernel.org/doc/html/latest/process/coding-style.html
+.. _`MISRA C:2012 Guidelines`: https://www.misra.org.uk/Activities/MISRAC/tabid/160/Default.aspx
+.. _`a spreadsheet`: https://developer.trustedfirmware.org/file/download/lamajxif3w7c4mpjeoo5/PHID-FILE-fp7c7acszn6vliqomyhn/MISRA-and-TF-Analysis-v1.3.ods