In the current code, if we fail during a frequency transition we simply send the
POSTCHANGE notification with old frequency. This isn't enough.
One of the core user of these notifications is the code responsible for keeping
loops_per_jiffy aligned with frequency change. And mostly it is written as:
if ((val == CPUFREQ_PRECHANGE && freq->old < freq->new) ||
(val == CPUFREQ_POSTCHANGE && freq->old > freq->new)) {
update-loops-per-jiffy...
}
So, suppose we are changing to a higher frequency and failed during transition,
then following will happen:
- CPUFREQ_PRECHANGE notification with freq-new > freq-old
- CPUFREQ_POSTCHANGE notification with freq-new == freq-old
The first one will update loops_per_jiffy and second one will do nothing. Even
if we send the 2nd notification by exchanging values of freq-new and old, some
users of these notifications might get unstable.
This can be fixed by simply calling cpufreq_notify_post_transition() with error
code and this routine will take care of sending notifications in correct order.
Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
---
drivers/cpufreq/cpufreq.c | 13 ++-----------
1 file changed, 2 insertions(+), 11 deletions(-)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 3b877d4..a7fcb84 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1815,17 +1815,8 @@ int __cpufreq_driver_target(struct cpufreq_policy *policy,
pr_err("%s: Failed to change cpu frequency: %d\n",
__func__, retval);
- if (notify) {
- /*
- * Notify with old freq in case we failed to change
- * frequency
- */
- if (retval)
- freqs.new = freqs.old;
-
- cpufreq_notify_transition(policy, &freqs,
- CPUFREQ_POSTCHANGE);
- }
+ if (notify)
+ cpufreq_notify_post_transition(policy, &freqs, retval);
}
out:
--
1.7.12.rc2.18.g61b472e
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