mpm: sys_utils: add libgpiod-based Gpio helper

This adds a new Gpio helper class, which uses libgpiod under the
hood instead of the deprecated sysfs GPIO access. This class provides
the ability to get/set a specific GPIO, which is looked up by name.

4 files changed, 143 insertions, 6 deletions

diff --git a/mpm/python/tests/base_tests.py b/mpm/python/tests/base_tests.py
index ec4b8328a..cb57b3481 100755
--- a/mpm/python/tests/base_tests.py
+++ b/mpm/python/tests/base_tests.py
@@ -7,7 +7,7 @@
 Base Test Case classes
 """
 
-import platform
+from test_utilities import on_linux, on_usrp
 import unittest
 
 class TestBase(unittest.TestCase):
@@ -19,7 +19,7 @@ class TestBase(unittest.TestCase):
         Test function decorator which skips tests unless the current
         execution environment is a linux OS.
         """
-        if 'linux' in platform.system().lower():
+        if on_linux():
             return lambda func: func
         return unittest.skip("This test is only valid when run on a Linux system.")
 
@@ -27,11 +27,8 @@ class TestBase(unittest.TestCase):
         """
         Test function decorator which skips tests unless the current
         execution environment is a USRP.
-
-        Assumes that 'arm' in the machine name constitutes an ARM
-        processor, aka a USRP.
         """
-        if 'arm' in platform.machine().lower():
+        if on_usrp():
             return lambda func: func
         return unittest.skip("This test is only valid when run on the USRP.")
 
diff --git a/mpm/python/tests/sys_utils_tests.py b/mpm/python/tests/sys_utils_tests.py
index c21cfea07..50a10e1a1 100755
--- a/mpm/python/tests/sys_utils_tests.py
+++ b/mpm/python/tests/sys_utils_tests.py
@@ -9,6 +9,7 @@ Tests related to usrp_mpm.sys_utils
 
 from base_tests import TestBase
 import unittest
+import test_utilities
 from usrp_mpm.sys_utils import net
 import platform
 
diff --git a/mpm/python/tests/test_utilities.py b/mpm/python/tests/test_utilities.py
index 210e76580..198eda5e8 100755
--- a/mpm/python/tests/test_utilities.py
+++ b/mpm/python/tests/test_utilities.py
@@ -6,6 +6,80 @@
 """ Utility classes to facilitate unit testing """
 
 import queue
+import platform
+import os
+
+def on_linux():
+    """
+    Returns True if this is being executed on a Linux system
+    """
+    return 'linux' in platform.system().lower()
+
+def on_usrp():
+    """
+    Returns True if this is being executed on an USRP
+    """
+    # Check device tree standard property for manufacturer info
+    path = '/sys/firmware/devicetree/base/compatible'
+
+    if not os.path.exists(path):
+        return False
+    else:
+        with open(path, 'r') as f:
+            s = f.read()
+            # String returned is actually a list of null-terminated strings,
+            # replace the null-terminations with a separator
+            s.replace('\x00', ';')
+            return 'ettus' in s
+
+def _mock_gpiod_pkg():
+    """
+    Replace the gpiod python package with a mock version if import
+    of the gpiod package fails. This package is not available on all
+    OS versions that we would like to test in.
+    """
+    try:
+        import gpiod
+    except Exception as ex:
+        # The gpiod package should be available if testing on a USRP
+        if on_usrp():
+            raise ex
+        import sys
+        sys.modules["gpiod"] = MockGpiod
+
+class MockGpiod(object):
+    """
+    Mocks a portion of the gpiod python package without actually
+    accessing GPIO hardware.
+    """
+    LINE_REQ_DIR_IN = 0
+    LINE_REQ_DIR_OUT = 1
+
+    _DEFAULT_LINE_VAL = 0
+
+    class MockLine(object):
+        def __init__(self, val):
+            self.val = val
+
+        def request(self):
+            pass
+
+        def release(self):
+            pass
+
+        def get_value(self):
+            return self.val
+
+        def set_value(self, val):
+            self.val = val
+
+    def __init__(self):
+        self.lines = dict()
+
+    def find_line(self, name):
+        if name not in self.lines.keys():
+            self.lines[name] = self.MockLine(self._DEFAULT_LINE_VAL)
+        return self.lines[name]
 
 class MockRegsIface(object):
     """
@@ -111,3 +185,8 @@ class MockLog(object):
             return ''
         else:
             return log_messages.get_nowait()
+
+# importing this utilities package should mock out the gpiod package
+# if necessary so that usrp_mpm can be imported on devices without
+# gpiod support for the OS.
+_mock_gpiod_pkg()
diff --git a/mpm/python/usrp_mpm/sys_utils/gpio.py b/mpm/python/usrp_mpm/sys_utils/gpio.py
new file mode 100644
index 000000000..b609479f1
--- /dev/null
+++ b/mpm/python/usrp_mpm/sys_utils/gpio.py
@@ -0,0 +1,60 @@
+#
+# Copyright 2020 Ettus Research, a National Instruments Brand
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+#
+"""
+Access to GPIOs via libgpiod
+"""
+
+import contextlib
+import gpiod
+
+
+@contextlib.contextmanager
+def request_gpio(line, direction):
+    """
+    Context manager for a GPIO line
+    """
+    line.request(consumer='mpm', type=direction)
+    try:
+        yield line
+    finally:
+        line.release()
+
+
+class Gpio:
+    """
+    Class for accessing a named GPIO line via libgpiod
+    """
+
+    INPUT = gpiod.LINE_REQ_DIR_IN
+    OUTPUT = gpiod.LINE_REQ_DIR_OUT
+
+    def __init__(self, name, direction=INPUT, default_val=None):
+        self._direction = direction
+        self._line = gpiod.find_line(name)
+        self._out_value = False
+        if self._line is None:
+            raise RuntimeError('failed to find gpio with name %s' % name)
+
+        if default_val is not None and direction == Gpio.OUTPUT:
+            self.set(default_val)
+
+    def get(self):
+        """
+        Read the value of this GPIO
+        """
+        if self._direction == self.OUTPUT:
+            return self._out_value
+
+        with request_gpio(self._line, self._direction) as gpio:
+            return bool(gpio.get_value())
+
+    def set(self, value):
+        """
+        Set the value of this GPIO
+        """
+        with request_gpio(self._line, self._direction) as gpio:
+            gpio.set_value(int(value))
+            self._out_value = bool(value)