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.
Also it returns a proper error message in case frequency transition failed.
Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
---
drivers/cpufreq/unicore2-cpufreq.c | 16 +++++++---------
1 file changed, 7 insertions(+), 9 deletions(-)
diff --git a/drivers/cpufreq/unicore2-cpufreq.c b/drivers/cpufreq/unicore2-cpufreq.c
index 951152f..99d280d6 100644
--- a/drivers/cpufreq/unicore2-cpufreq.c
+++ b/drivers/cpufreq/unicore2-cpufreq.c
@@ -38,19 +38,17 @@ static int ucv2_target(struct cpufreq_policy *policy,
unsigned int target_freq,
unsigned int relation)
{
- unsigned int cur = policy->cur;
struct cpufreq_freqs freqs;
+ int ret;
- cpufreq_notify_transition(policy, &freqs, CPUFREQ_PRECHANGE);
-
- if (!clk_set_rate(policy->clk, target_freq * 1000)) {
- freqs.old = cur;
- freqs.new = target_freq;
- }
+ freqs.old = policy->cur;
+ freqs.new = target_freq;
- cpufreq_notify_transition(policy, &freqs, CPUFREQ_POSTCHANGE);
+ cpufreq_notify_transition(policy, &freqs, CPUFREQ_PRECHANGE);
+ ret = clk_set_rate(policy->clk, target_freq * 1000);
+ cpufreq_notify_post_transition(policy, &freqs, ret);
- return 0;
+ return ret;
}
static int __init ucv2_cpu_init(struct cpufreq_policy *policy)
--
1.7.12.rc2.18.g61b472e
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