A script to create ACPI based GPIO mapping.

src/platform/utils/gpio_setup.py

Index: src/platform/utils/gpio_setup.py
diff --git a/src/platform/utils/gpio_setup.py b/src/platform/utils/gpio_setup.py
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+#!/usr/bin/python
+
+# Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""A script to create symlinks to platform specific GPIO pins.
+
+This script creates a set of symlinks pointing at the sys fs files returning
+the appropriate GPIO pin values. Each symlink is named to represent the actual
+GPIO pin function.
+
+The location of the symlinks generated by this script can be specified using
+the --symlink_root command line option. By default /home/gpio directory is
+used. The symlink directory must exist before this script is run.
+
+The GPIO pins' values are available through a GPIO device present in sys fs.
+The device is identified by its PCI bus address. The default PCI address of
+the GPIO device (set to 0:0:1f.0), can be changed using the --pci_address
+command line option.
+
+The platform specific bit usage of the GPIO device is derived from the ACPI,
+also using files found in a fixed location in sys fs. The default location of
+/sys/bus/platform/devices/chromeos_acpi could be changed using the --acpi_root
+command line option.
+
+Each GPIO pin is represented through ACPI as a subdirectory with several files
+in it. A typical name of the GPIO pin file looks as follows:
+
+<acpi_root>/GPIO.<instance>/GPIO.[0-3]
+
+where <instance> is a zero based number assigned to this GPIO pin by the BIOS.
+
+In particular, file GPIO.0 represents encoded pin signal type (from which the
+symlink name is derived), and file GPIO.2 represents the actual zero based
+GPIO pin number within this GPIO device range.
+
+This script reads the ACPI provided mapping, enables the appropriate GPIO pins
+and creates symlinks mapping these GPIOs' values.
+"""
+
+__author__ = 'The Chromium OS Authors'
+
+import glob
+import os
+import optparse
+import sys
+
+GPIO_ROOT = '/sys/class/gpio'
+GPIO_DEVICE_ROOT = GPIO_ROOT + '/gpiochip'
+GPIO_ENABLE_FILE = '/sys/class/gpio/' + 'export'
+
+# Can be changed using --pci_address command line option.
+GPIO_DEVICE_PCI_ADDRESS = '0000:00:1f.0'
+
+# Can be changed using --acpi_root command line option.
+ACPI_ROOT = '/sys/bus/platform/devices/chromeos_acpi'
+GPIO_SIGNAL_TYPE_EXTENSION = '0'
+GPIO_PIN_NUMBER_EXTENSION = '2'
+
+# can be changed using --symlink_root command line option.
+DEFAULT_SYMLINK_ROOT = '/home/gpio'
+
+# This dictionary maps GPIO signal types codes into their actual names.
+GPIO_SIGNAL_TYPES = {
+    1: 'recovery_button',
+    2: 'developer_switch',
+    3: 'write_protect'
+    }
+
+# Debug header signal type codes are offset by 0x100, the tuple below
+# represents the range of valid codes for the debug header. The range starts
+# at 0x100 and is 0x100 wide.
+GPIO_DEBUG_HEADER_RANGE = (0x100, 0x100)
+
+# This is used to prepare the option parser: each element is a tuple of
+# strings, including the option name and the option default value.
+option_list = (('symlink_root', DEFAULT_SYMLINK_ROOT),
+               ('pci_address', GPIO_DEVICE_PCI_ADDRESS),
+               ('acpi_root', ACPI_ROOT))
+
+# This becomes the option object after the command line is parsed.
+cmd_line_options = None
+
+class GpioSetupError(Exception):
+  pass
+
+
+class GpioChip(object):
+  """Represent GPIO chip available through sys fs.
+
+  Attributes:
+    pci_address: a string, PCI address of this GPIO device
+    base: a number, base global GPIO number of this device (mapped to pin zero
+          in the device range)
+    capacity: a number, shows the number of GPIO pins of this device.
+    description: a multiline string description of this device, initialized
+                 after the device is attached. Can be used to dump device
+                 information.
+  """
+
+  def __init__(self, pci_address):
+    self.pci_address = pci_address
+    self.base = 0
+    self.capacity = 0
+    self.description = 'not attached'
+
+  def Attach(self):
+    for f in glob.glob(GPIO_DEVICE_ROOT + '*/label'):
+      label = open(f).read().strip()
+      if label == self.pci_address:
+        break
+    else:
+      raise GpioSetupError(
+          'could not find GPIO PCI device %s' % self.pci_address)
+    directory = os.path.dirname(f)
+    self.base = int(open(directory + '/base').read())
+    self.capacity = int(open(directory + '/ngpio').read())
+    self.description = '\n'.join(['GPIO device at PCI address %s' %
+                                  self.pci_address,
+                                  'Base gpio pin %d' % self.base,
+                                  'Capacity %d' % self.capacity])
+
+  def EnablePin(self, pin):
+    """Enable a certain GPIO pin.
+
+    To enable the pin one needs to write its global GPIO number into
+    /sys/class/gpio/export, if this pin has not been enabled yet.
+
+    Inputs:
+      pin: a number, zero based pin number within this device's range.
+    """
+
+    if pin >= self.capacity:
+      raise GpioSetupError('pin %d exceeds capacity of %d' % (
+          pin, self.capacity))
+    global_gpio_number = self.base + pin
+    if not os.path.exists('%s/gpio%d' % (GPIO_ROOT, global_gpio_number)):
+      open(GPIO_ENABLE_FILE, 'w').write('%d' % (global_gpio_number))
+
+  def __str__(self):
+    return self.description
+
+
+def ParseAcpiMappings():
+  """Scan ACPI information about GPIO and generate a mapping.
+
+  Returns: a list of tuples, each tuple consisting of a string representing
+           the GPIO pin name and a number, representing the GPIO pin within
+           the GPIO device space.
+  """
+  acpi_gpio_mapping = []
+  for d in glob.glob('%s/GPIO.[0-9]*' % cmd_line_options.acpi_root):
+    signal_type = int(open('%s/GPIO.%s' % (
+        d, GPIO_SIGNAL_TYPE_EXTENSION)).read())
+
+    pin_number = int(open('%s/GPIO.%s' % (
+        d, GPIO_PIN_NUMBER_EXTENSION)).read())
+
+    if signal_type in GPIO_SIGNAL_TYPES:
+      acpi_gpio_mapping.append((GPIO_SIGNAL_TYPES[signal_type], pin_number))
+      continue
+
+    # This is not a specific signal, could be a debug header pin.
+    debug_header = signal_type - GPIO_DEBUG_HEADER_RANGE[0]
+    if debug_header >= 0 and debug_header < GPIO_DEBUG_HEADER_RANGE[1]:
+      acpi_gpio_mapping.append(('debug_header_%d' % debug_header, pin_number))
+      continue
+
+    # Unrecognized mapping, could happen if BIOS version is ahead of this
+    # script.
+    print 'unknown signal type encoding %d in %d' % (signal_type, d)
+
+  if not acpi_gpio_mapping:
+    raise GpioSetupError('no gpio mapping found. Is ACPI driver installed?')
+
+  return acpi_gpio_mapping
+
+
+def CreateGpioSymlinks(mappings, gpio, symlink_root):
+  if not os.path.exists(symlink_root):
+    raise GpioSetupError('%s does not exist' % symlink_root)
+
+  if not os.path.isdir(symlink_root):
+    raise GpioSetupError('%s is not a directory' % symlink_root)
+
+  if not os.access(symlink_root, os.W_OK):
+    raise GpioSetupError('%s is not writable' % symlink_root)
+
+  try:
+    os.chdir(symlink_root)
+  except OSError:
+    raise GpioSetupError('failed to change directory to %s' % symlink_root)
+
+  for (symlink, pin) in mappings:
+    gpio.EnablePin(pin)
+    source_file = '%s/gpio%d/value' % (GPIO_ROOT, pin + gpio.base)
+    if not os.path.exists(symlink):
+      os.symlink(source_file, symlink)
+      continue
+    if not os.path.islink(symlink):
+      raise GpioSetupError(
+          '%s exists but is not a symlink' % os.path.abspath(symlink))
+    if os.readlink(symlink) != source_file:
+      raise GpioSetupError(
+          '%s points to a wrong file' % os.path.abspath(symlink))
+
+
+def ProcessOptions():
+  global cmd_line_options
+  parser = optparse.OptionParser()
+  for (name, default_value) in option_list:
+    parser.add_option('--' + name, dest=name, default=default_value)
+  (cmd_line_options, _) = parser.parse_args()
+
+
+def main():
+  ProcessOptions()
+  gpioc = GpioChip(cmd_line_options.pci_address)
+  gpioc.Attach()
+  CreateGpioSymlinks(ParseAcpiMappings(), gpioc, cmd_line_options.symlink_root)
+
+
+if __name__ == '__main__':
+  try:
+    main()
+  except GpioSetupError, e:
+    print >> sys.stderr, '%s: %s' % (sys.argv[0].split('/')[-1], e)
+    sys.exit(1)
+  sys.exit(0)