fdt: Add Python bindings

An early version of this is available upstream. Bring it in as a starting
point. This is from dtc upstream commit e56f2b0.

Future work will plumb it into dtoc and remove the now-unnecessary local
libraries.

Signed-off-by: Simon Glass <sjg@chromium.org>

lib/libfdt/pylibfdt/libfdt.i

+/*
+ * pylibfdt - Flat Device Tree manipulation in Python
+ * Copyright (C) 2017 Google, Inc.
+ * Written by Simon Glass <sjg@chromium.org>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+ BSD-2-Clause
+ */
+
+%module libfdt
+
+%{
+#define SWIG_FILE_WITH_INIT
+#include "libfdt.h"
+%}
+
+%pythoncode %{
+
+import struct
+
+# Error codes, corresponding to FDT_ERR_... in libfdt.h
+(NOTFOUND,
+        EXISTS,
+        NOSPACE,
+        BADOFFSET,
+        BADPATH,
+        BADPHANDLE,
+        BADSTATE,
+        TRUNCATED,
+        BADMAGIC,
+        BADVERSION,
+        BADSTRUCTURE,
+        BADLAYOUT,
+        INTERNAL,
+        BADNCELLS,
+        BADVALUE,
+        BADOVERLAY,
+        NOPHANDLES) = QUIET_ALL = range(1, 18)
+# QUIET_ALL can be passed as the 'quiet' parameter to avoid exceptions
+# altogether. All # functions passed this value will return an error instead
+# of raising an exception.
+
+# Pass this as the 'quiet' parameter to return -ENOTFOUND on NOTFOUND errors,
+# instead of raising an exception.
+QUIET_NOTFOUND = (NOTFOUND,)
+
+
+class FdtException(Exception):
+    """An exception caused by an error such as one of the codes above"""
+    def __init__(self, err):
+        self.err = err
+
+    def __str__(self):
+        return 'pylibfdt error %d: %s' % (self.err, fdt_strerror(self.err))
+
+def strerror(fdt_err):
+    """Get the string for an error number
+
+    Args:
+        fdt_err: Error number (-ve)
+
+    Returns:
+        String containing the associated error
+    """
+    return fdt_strerror(fdt_err)
+
+def check_err(val, quiet=()):
+    """Raise an error if the return value is -ve
+
+    This is used to check for errors returned by libfdt C functions.
+
+    Args:
+        val: Return value from a libfdt function
+        quiet: Errors to ignore (empty to raise on all errors)
+
+    Returns:
+        val if val >= 0
+
+    Raises
+        FdtException if val < 0
+    """
+    if val < 0:
+        if -val not in quiet:
+            raise FdtException(val)
+    return val
+
+def check_err_null(val, quiet=()):
+    """Raise an error if the return value is NULL
+
+    This is used to check for a NULL return value from certain libfdt C
+    functions
+
+    Args:
+        val: Return value from a libfdt function
+        quiet: Errors to ignore (empty to raise on all errors)
+
+    Returns:
+        val if val is a list, None if not
+
+    Raises
+        FdtException if val indicates an error was reported and the error
+        is not in @quiet.
+    """
+    # Normally a list is returned which contains the data and its length.
+    # If we get just an integer error code, it means the function failed.
+    if not isinstance(val, list):
+        if -val not in quiet:
+            raise FdtException(val)
+    return val
+
+class Fdt:
+    """Device tree class, supporting all operations
+
+    The Fdt object is created is created from a device tree binary file,
+    e.g. with something like:
+
+       fdt = Fdt(open("filename.dtb").read())
+
+    Operations can then be performed using the methods in this class. Each
+    method xxx(args...) corresponds to a libfdt function fdt_xxx(fdt, args...).
+
+    All methods raise an FdtException if an error occurs. To avoid this
+    behaviour a 'quiet' parameter is provided for some functions. This
+    defaults to empty, but you can pass a list of errors that you expect.
+    If one of these errors occurs, the function will return an error number
+    (e.g. -NOTFOUND).
+    """
+    def __init__(self, data):
+        self._fdt = bytearray(data)
+        check_err(fdt_check_header(self._fdt));
+
+    def path_offset(self, path, quiet=()):
+        """Get the offset for a given path
+
+        Args:
+            path: Path to the required node, e.g. '/node@3/subnode@1'
+            quiet: Errors to ignore (empty to raise on all errors)
+
+        Returns:
+            Node offset
+
+        Raises
+            FdtException if the path is not valid or not found
+        """
+        return check_err(fdt_path_offset(self._fdt, path), quiet)
+
+    def first_property_offset(self, nodeoffset, quiet=()):
+        """Get the offset of the first property in a node offset
+
+        Args:
+            nodeoffset: Offset to the node to check
+            quiet: Errors to ignore (empty to raise on all errors)
+
+        Returns:
+            Offset of the first property
+
+        Raises
+            FdtException if the associated node has no properties, or some
+                other error occurred
+        """
+        return check_err(fdt_first_property_offset(self._fdt, nodeoffset),
+                         quiet)
+
+    def next_property_offset(self, prop_offset, quiet=()):
+        """Get the next property in a node
+
+        Args:
+            prop_offset: Offset of the previous property
+            quiet: Errors to ignore (empty to raise on all errors)
+
+        Returns:
+            Offset of the next property
+
+        Raises:
+            FdtException if the associated node has no more properties, or
+                some other error occurred
+        """
+        return check_err(fdt_next_property_offset(self._fdt, prop_offset),
+                         quiet)
+
+    def get_name(self, nodeoffset):
+        """Get the name of a node
+
+        Args:
+            nodeoffset: Offset of node to check
+
+        Returns:
+            Node name
+
+        Raises:
+            FdtException on error (e.g. nodeoffset is invalid)
+        """
+        return check_err_null(fdt_get_name(self._fdt, nodeoffset))[0]
+
+    def get_property_by_offset(self, prop_offset, quiet=()):
+        """Obtains a property that can be examined
+
+        Args:
+            prop_offset: Offset of property (e.g. from first_property_offset())
+            quiet: Errors to ignore (empty to raise on all errors)
+
+        Returns:
+            Property object, or None if not found
+
+        Raises:
+            FdtException on error (e.g. invalid prop_offset or device
+            tree format)
+        """
+        pdata = check_err_null(
+                fdt_get_property_by_offset(self._fdt, prop_offset), quiet)
+        if isinstance(pdata, (int)):
+            return pdata
+        return Property(pdata[0], pdata[1])
+
+    def first_subnode(self, nodeoffset, quiet=()):
+        """Find the first subnode of a parent node
+
+        Args:
+            nodeoffset: Node offset of parent node
+            quiet: Errors to ignore (empty to raise on all errors)
+
+        Returns:
+            The offset of the first subnode, if any
+
+        Raises:
+            FdtException if no subnode found or other error occurs
+        """
+        return check_err(fdt_first_subnode(self._fdt, nodeoffset), quiet)
+
+    def next_subnode(self, nodeoffset, quiet=()):
+        """Find the next subnode
+
+        Args:
+            nodeoffset: Node offset of previous subnode
+            quiet: Errors to ignore (empty to raise on all errors)
+
+        Returns:
+            The offset of the next subnode, if any
+
+        Raises:
+            FdtException if no more subnode found or other error occurs
+        """
+        return check_err(fdt_next_subnode(self._fdt, nodeoffset), quiet)
+
+    def totalsize(self):
+        """Return the total size of the device tree
+
+        Returns:
+            Total tree size in bytes
+        """
+        return check_err(fdt_totalsize(self._fdt))
+
+    def off_dt_struct(self):
+        """Return the start of the device tree struct area
+
+        Returns:
+            Start offset of struct area
+        """
+        return check_err(fdt_off_dt_struct(self._fdt))
+
+    def pack(self, quiet=()):
+        """Pack the device tree to remove unused space
+
+        This adjusts the tree in place.
+
+        Args:
+            quiet: Errors to ignore (empty to raise on all errors)
+
+        Raises:
+            FdtException if any error occurs
+        """
+        return check_err(fdt_pack(self._fdt), quiet)
+
+    def delprop(self, nodeoffset, prop_name):
+        """Delete a property from a node
+
+        Args:
+            nodeoffset: Node offset containing property to delete
+            prop_name: Name of property to delete
+
+        Raises:
+            FdtError if the property does not exist, or another error occurs
+        """
+        return check_err(fdt_delprop(self._fdt, nodeoffset, prop_name))
+
+    def getprop(self, nodeoffset, prop_name, quiet=()):
+        """Get a property from a node
+
+        Args:
+            nodeoffset: Node offset containing property to get
+            prop_name: Name of property to get
+            quiet: Errors to ignore (empty to raise on all errors)
+
+        Returns:
+            Value of property as a bytearray, or -ve error number
+
+        Raises:
+            FdtError if any error occurs (e.g. the property is not found)
+        """
+        pdata = check_err_null(fdt_getprop(self._fdt, nodeoffset, prop_name),
+                               quiet)
+        if isinstance(pdata, (int)):
+            return pdata
+        return bytearray(pdata[0])
+
+
+class Property:
+    """Holds a device tree property name and value.
+
+    This holds a copy of a property taken from the device tree. It does not
+    reference the device tree, so if anything changes in the device tree,
+    a Property object will remain valid.
+
+    Properties:
+        name: Property name
+        value: Proper value as a bytearray
+    """
+    def __init__(self, name, value):
+        self.name = name
+        self.value = value
+%}
+
+%rename(fdt_property) fdt_property_func;
+
+typedef int fdt32_t;
+
+%include "libfdt/fdt.h"
+
+%include "typemaps.i"
+
+/* Most functions don't change the device tree, so use a const void * */
+%typemap(in) (const void *)(const void *fdt) {
+	if (!PyByteArray_Check($input)) {
+		SWIG_exception_fail(SWIG_TypeError, "in method '" "$symname"
+			"', argument " "$argnum"" of type '" "$type""'");
+	}
+	$1 = (void *)PyByteArray_AsString($input);
+        fdt = $1;
+        fdt = fdt; /* avoid unused variable warning */
+}
+
+/* Some functions do change the device tree, so use void * */
+%typemap(in) (void *)(const void *fdt) {
+	if (!PyByteArray_Check($input)) {
+		SWIG_exception_fail(SWIG_TypeError, "in method '" "$symname"
+			"', argument " "$argnum"" of type '" "$type""'");
+	}
+	$1 = PyByteArray_AsString($input);
+        fdt = $1;
+        fdt = fdt; /* avoid unused variable warning */
+}
+
+%typemap(out) (struct fdt_property *) {
+	PyObject *buff;
+
+	if ($1) {
+		resultobj = PyString_FromString(
+			fdt_string(fdt1, fdt32_to_cpu($1->nameoff)));
+		buff = PyByteArray_FromStringAndSize(
+			(const char *)($1 + 1), fdt32_to_cpu($1->len));
+		resultobj = SWIG_Python_AppendOutput(resultobj, buff);
+	}
+}
+
+%apply int *OUTPUT { int *lenp };
+
+/* typemap used for fdt_getprop() */
+%typemap(out) (const void *) {
+	if (!$1)
+		$result = Py_None;
+	else
+		$result = Py_BuildValue("s#", $1, *arg4);
+}
+
+/* We have both struct fdt_property and a function fdt_property() */
+%warnfilter(302) fdt_property;
+
+/* These are macros in the header so have to be redefined here */
+int fdt_magic(const void *fdt);
+int fdt_totalsize(const void *fdt);
+int fdt_off_dt_struct(const void *fdt);
+int fdt_off_dt_strings(const void *fdt);
+int fdt_off_mem_rsvmap(const void *fdt);
+int fdt_version(const void *fdt);
+int fdt_last_comp_version(const void *fdt);
+int fdt_boot_cpuid_phys(const void *fdt);
+int fdt_size_dt_strings(const void *fdt);
+int fdt_size_dt_struct(const void *fdt);
+
+%include <../libfdt/libfdt.h>

lib/libfdt/pylibfdt/setup.py

+#!/usr/bin/env python
+
+"""
+setup.py file for SWIG libfdt
+Copyright (C) 2017 Google, Inc.
+Written by Simon Glass <sjg@chromium.org>
+
+SPDX-License-Identifier:	GPL-2.0+ BSD-2-Clause
+
+Files to be built into the extension are provided in SOURCES
+C flags to use are provided in CPPFLAGS
+Object file directory is provided in OBJDIR
+Version is provided in VERSION
+
+If these variables are not given they are parsed from the Makefiles. This
+allows this script to be run stand-alone, e.g.:
+
+    ./pylibfdt/setup.py install [--prefix=...]
+"""
+
+from distutils.core import setup, Extension
+import os
+import re
+import sys
+
+# Decodes a Makefile assignment line into key and value (and plus for +=)
+RE_KEY_VALUE = re.compile('(?P<key>\w+) *(?P<plus>[+])?= *(?P<value>.*)$')
+
+
+def ParseMakefile(fname):
+    """Parse a Makefile to obtain its variables.
+
+    This collects variable assigments of the form:
+
+        VAR = value
+        VAR += more
+
+    It does not pick out := assignments, as these are not needed here. It does
+    handle line continuation.
+
+    Returns a dict:
+        key: Variable name (e.g. 'VAR')
+        value: Variable value (e.g. 'value more')
+    """
+    makevars = {}
+    with open(fname) as fd:
+        prev_text = ''  # Continuation text from previous line(s)
+        for line in fd.read().splitlines():
+          if line and line[-1] == '\\':  # Deal with line continuation
+            prev_text += line[:-1]
+            continue
+          elif prev_text:
+            line = prev_text + line
+            prev_text = ''  # Continuation is now used up
+          m = RE_KEY_VALUE.match(line)
+          if m:
+            value = m.group('value') or ''
+            key = m.group('key')
+
+            # Appending to a variable inserts a space beforehand
+            if 'plus' in m.groupdict() and key in makevars:
+              makevars[key] += ' ' + value
+            else:
+              makevars[key] = value
+    return makevars
+
+def GetEnvFromMakefiles():
+    """Scan the Makefiles to obtain the settings we need.
+
+    This assumes that this script is being run from the top-level directory,
+    not the pylibfdt directory.
+
+    Returns:
+        Tuple with:
+            List of swig options
+            Version string
+            List of files to build
+            List of extra C preprocessor flags needed
+            Object directory to use (always '')
+    """
+    basedir = os.path.dirname(os.path.dirname(os.path.abspath(sys.argv[0])))
+    swig_opts = ['-I%s' % basedir]
+    makevars = ParseMakefile(os.path.join(basedir, 'Makefile'))
+    version = '%s.%s.%s' % (makevars['VERSION'], makevars['PATCHLEVEL'],
+                            makevars['SUBLEVEL'])
+    makevars = ParseMakefile(os.path.join(basedir, 'libfdt', 'Makefile.libfdt'))
+    files = makevars['LIBFDT_SRCS'].split()
+    files = [os.path.join(basedir, 'libfdt', fname) for fname in files]
+    files.append('pylibfdt/libfdt.i')
+    cflags = ['-I%s' % basedir, '-I%s/libfdt' % basedir]
+    objdir = ''
+    return swig_opts, version, files, cflags, objdir
+
+
+progname = sys.argv[0]
+files = os.environ.get('SOURCES', '').split()
+cflags = os.environ.get('CPPFLAGS', '').split()
+objdir = os.environ.get('OBJDIR')
+version = os.environ.get('VERSION')
+swig_opts = []
+
+# If we were called directly rather than through our Makefile (which is often
+# the case with Python module installation), read the settings from the
+# Makefile.
+if not all((version, files, cflags, objdir)):
+    swig_opts, version, files, cflags, objdir = GetEnvFromMakefiles()
+
+libfdt_module = Extension(
+    '_libfdt',
+    sources = files,
+    extra_compile_args = cflags,
+    swig_opts = swig_opts,
+)
+
+setup(
+    name='libfdt',
+    version= version,
+    author='Simon Glass <sjg@chromium.org>',
+    description='Python binding for libfdt',
+    ext_modules=[libfdt_module],
+    package_dir={'': objdir},
+    py_modules=['pylibfdt/libfdt'],
+)