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 fills freqs.old before starting the first notification, this was missing since ever.
Signed-off-by: Viresh Kumar viresh.kumar@linaro.org --- drivers/cpufreq/pcc-cpufreq.c | 18 +++++++----------- 1 file changed, 7 insertions(+), 11 deletions(-)
diff --git a/drivers/cpufreq/pcc-cpufreq.c b/drivers/cpufreq/pcc-cpufreq.c index e2b4f40..1c0f106 100644 --- a/drivers/cpufreq/pcc-cpufreq.c +++ b/drivers/cpufreq/pcc-cpufreq.c @@ -213,6 +213,7 @@ static int pcc_cpufreq_target(struct cpufreq_policy *policy, cpu, target_freq, (pcch_virt_addr + pcc_cpu_data->input_offset));
+ freqs.old = policy->cur; freqs.new = target_freq; cpufreq_notify_transition(policy, &freqs, CPUFREQ_PRECHANGE);
@@ -228,25 +229,20 @@ static int pcc_cpufreq_target(struct cpufreq_policy *policy, memset_io((pcch_virt_addr + pcc_cpu_data->input_offset), 0, BUF_SZ);
status = ioread16(&pcch_hdr->status); + iowrite16(0, &pcch_hdr->status); + + cpufreq_notify_post_transition(policy, &freqs, status != CMD_COMPLETE); + spin_unlock(&pcc_lock); + if (status != CMD_COMPLETE) { pr_debug("target: FAILED for cpu %d, with status: 0x%x\n", cpu, status); - goto cmd_incomplete; + return -EINVAL; } - iowrite16(0, &pcch_hdr->status);
- cpufreq_notify_transition(policy, &freqs, CPUFREQ_POSTCHANGE); pr_debug("target: was SUCCESSFUL for cpu %d\n", cpu); - spin_unlock(&pcc_lock);
return 0; - -cmd_incomplete: - freqs.new = freqs.old; - cpufreq_notify_transition(policy, &freqs, CPUFREQ_POSTCHANGE); - iowrite16(0, &pcch_hdr->status); - spin_unlock(&pcc_lock); - return -EINVAL; }
static int pcc_get_offset(int cpu)