Messages in this thread | | | Subject | Re: [PATCH v2 18/18] cpufreq: scmi: add support for fast frequency switching | From | Sudeep Holla <> | Date | Wed, 9 Aug 2017 11:09:02 +0100 |
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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" <rjw@rjwysocki.net> >> Cc: Viresh Kumar <viresh.kumar@linaro.org> >> Cc: linux-pm@vger.kernel.org >> Signed-off-by: Sudeep Holla <sudeep.holla@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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