mpm: Add convenience function to pull i2c bus from device tree

This function grabs the i2c character device path from the OF_NAME
property. That property must be unique in the device tree!

2 files changed, 37 insertions, 0 deletions

diff --git a/mpm/python/usrp_mpm/sys_utils/CMakeLists.txt b/mpm/python/usrp_mpm/sys_utils/CMakeLists.txt
index ee7c249df..e1d830c94 100644
--- a/mpm/python/usrp_mpm/sys_utils/CMakeLists.txt
+++ b/mpm/python/usrp_mpm/sys_utils/CMakeLists.txt
@@ -8,6 +8,7 @@ SET(USRP_MPM_FILES ${USRP_MPM_FILES})
 SET(USRP_MPM_SYSUTILS_FILES
     ${CMAKE_CURRENT_SOURCE_DIR}/__init__.py
     ${CMAKE_CURRENT_SOURCE_DIR}/dtoverlay.py
+    ${CMAKE_CURRENT_SOURCE_DIR}/i2c_dev.py
     ${CMAKE_CURRENT_SOURCE_DIR}/net.py
     ${CMAKE_CURRENT_SOURCE_DIR}/sysfs_gpio.py
     ${CMAKE_CURRENT_SOURCE_DIR}/sysfs_thermal.py
diff --git a/mpm/python/usrp_mpm/sys_utils/i2c_dev.py b/mpm/python/usrp_mpm/sys_utils/i2c_dev.py
new file mode 100644
index 000000000..7da5177f8
--- /dev/null
+++ b/mpm/python/usrp_mpm/sys_utils/i2c_dev.py
@@ -0,0 +1,36 @@
+#
+# Copyright 2018 Ettus Research, a National Instruments Company
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+#
+"""
+Utilities for i2c lookups
+"""
+
+import pyudev
+
+def of_get_i2c_adapter(of_name):
+    """
+    Return bus adapter device for given device tree name. To use the OF_NAME
+    for matching (as this function does), it must be a unique property in the
+    device tree (and this must be a device-tree platform).
+
+    The return value is a string, e.g. '/dev/i2c-0'. If nothing is found, it'll
+    return None.
+    """
+    # If has i2c-dev, follow to grab i2c-%d node
+    context = pyudev.Context()
+    parents = list(context.list_devices(subsystem="i2c-adapter", OF_NAME=of_name))
+    if len(parents) > 1:
+        raise RuntimeError("Non-unique OF_NAME when getting i2c bus id")
+    if len(parents) == 0:
+        return None
+    parent = parents[0]
+    if not parent:
+        return None
+    devices = list(context.list_devices(parent=parent, subsystem="i2c-dev"))
+    properties = [dict(d.properties) for d in devices]
+    # The i2c-adapter will have the lowest minor number
+    # FIXME: This likely isn't API--It just happens to work as of this writing
+    chosen = min([(int(p['MINOR']), p['DEVNAME']) for p in properties])
+    return chosen[1]