From 5c036ea669e6ea24b689eafdc7c2e5de9fcb9f52 Mon Sep 17 00:00:00 2001
From: Brendan Jackman <brendan.jackman@arm.com>
Date: Mon, 10 Apr 2017 17:39:13 +0100
Subject: [PATCH] cpufreq: Expose error when writing invalid governor tunable

If we get an TargetError when trying to set a governor tunable we currently fall
back to an older sysfs layout under the assumption that the file we tried to
write doesn't exist. However it may be that the file exists, but we tried to
write an invalid value (or something else went wrong). In this case we fall back
to the old file location, fail, and produce a nonsense error about the old path
not existing.

Instead, when we get a TargetError, check if the file exists, and fall back to
the old location only if it does not.
---
 devlib/module/cpufreq.py | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/devlib/module/cpufreq.py b/devlib/module/cpufreq.py
index e75a250..ff8a56d 100644
--- a/devlib/module/cpufreq.py
+++ b/devlib/module/cpufreq.py
@@ -152,10 +152,14 @@ class CpufreqModule(Module):
         valid_tunables = self.list_governor_tunables(cpu)
         for tunable, value in kwargs.iteritems():
             if tunable in valid_tunables:
+                path = '/sys/devices/system/cpu/{}/cpufreq/{}/{}'.format(cpu, governor, tunable)
                 try:
-                    path = '/sys/devices/system/cpu/{}/cpufreq/{}/{}'.format(cpu, governor, tunable)
                     self.target.write_value(path, value)
-                except TargetError:  # May be an older kernel
+                except TargetError:
+                    if self.target.file_exists(path):
+                        # File exists but we did something wrong
+                        raise
+                    # Expected file doesn't exist, try older sysfs layout.
                     path = '/sys/devices/system/cpu/cpufreq/{}/{}'.format(governor, tunable)
                     self.target.write_value(path, value)
             else: