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@linaro.org --- 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 a862aa9..557bb49 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -1764,17 +1764,8 @@ 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: