On 09/08/17 05:28, Viresh Kumar wrote:
> On 04-08-17, 15:31, Sudeep Holla wrote:
>> The cpufreq core provides option for drivers to implement fast_switch
>> callback which is invoked for frequency switching from interrupt context.
>>
>> This patch adds support for fast_switch callback in SCMI cpufreq driver
>> by making use of polling based SCMI transfer. It also sets the flag
>> fast_switch_possible.
>>
>> Cc: "Rafael J. Wysocki" <r...@rjwysocki.net>
>> Cc: Viresh Kumar <viresh.ku...@linaro.org>
>> Cc: linux...@vger.kernel.org
>> Signed-off-by: Sudeep Holla <sudeep.ho...@arm.com>
>> ---
>>  drivers/cpufreq/scmi-cpufreq.c | 16 ++++++++++++++++
>>  1 file changed, 16 insertions(+)
>>
>> diff --git a/drivers/cpufreq/scmi-cpufreq.c b/drivers/cpufreq/scmi-cpufreq.c
>> index 034359cafea5..cb1084cb1ef1 100644
>> --- a/drivers/cpufreq/scmi-cpufreq.c
>> +++ b/drivers/cpufreq/scmi-cpufreq.c
>> @@ -61,6 +61,19 @@ scmi_cpufreq_set_target(struct cpufreq_policy *policy, 
>> unsigned int index)
>>      return perf_ops->freq_set(priv->handle, priv->domain_id, freq, false);
>>  }
>>  
>> +static unsigned int scmi_cpufreq_fast_switch(struct cpufreq_policy *policy,
>> +                                         unsigned int target_freq)
>> +{
>> +    struct scmi_data *priv = policy->driver_data;
>> +    struct scmi_perf_ops *perf_ops = priv->handle->perf_ops;
>> +
>> +    if (!perf_ops->freq_set(priv->handle, priv->domain_id,
>> +                            target_freq * 1000, true))
>> +            return target_freq;
>> +
>> +    return CPUFREQ_ENTRY_INVALID;
>> +}
> 
> This is very much similar to the target routine, perhaps we should write 
> another
> local routine which is used by both target and fast switch.
> 

Just one difference, fast switch uses polling based mailbox while
target_index uses interrupt based. I thought initially to reuse, but
it's comes done to just perf_ops->freq_set, so dropped that idea.

> Do we guarantee that the frequency is changed by the time this routine 
> returns?

No, firmware may return acknowledging the request not it's completion.

> Or we just send a SCMI request and return back ?
> 

Yes, exactly.

> If we just send the request and don't wait for freq to get changed, what
> protects another scmi_cpufreq_fast_switch() to get called before the first one
> is finished? And what will happen on that call ?

Firmware needs to serialize or override based on the timing of the two
consecutive requests.

> 
>>  static int
>>  scmi_get_sharing_cpus(struct device *cpu_dev, struct cpumask *cpumask)
>>  {
>> @@ -164,6 +177,7 @@ static int scmi_cpufreq_init(struct cpufreq_policy 
>> *policy)
>>  
>>      policy->cpuinfo.transition_latency = latency;
>>  
>> +    policy->fast_switch_possible = true;
>>      return 0;
>>  
>>  out_free_cpufreq_table:
>> @@ -180,6 +194,7 @@ static int scmi_cpufreq_exit(struct cpufreq_policy 
>> *policy)
>>  {
>>      struct scmi_data *priv = policy->driver_data;
>>  
>> +    policy->fast_switch_possible = false;
>>      cpufreq_cooling_unregister(priv->cdev);
>>      dev_pm_opp_free_cpufreq_table(priv->cpu_dev, &policy->freq_table);
>>      dev_pm_opp_cpumask_remove_table(policy->related_cpus);
>> @@ -228,6 +243,7 @@ static struct cpufreq_driver scmi_cpufreq_driver = {
>>      .init                   = scmi_cpufreq_init,
>>      .exit                   = scmi_cpufreq_exit,
>>      .ready                  = scmi_cpufreq_ready,
>> +    .fast_switch            = scmi_cpufreq_fast_switch,
> 
> Maybe add it right after target_index ?
> 

Done

-- 
Regards,
Sudeep

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