[PATCH v2 18/18] cpufreq: scmi: add support for fast frequency switching

[Sudeep Holla <sudeep.holla@arm.com>]

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;
+}
+
 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,
 };
 
 static int scmi_cpufreq_probe(struct platform_device *pdev)
-- 
2.7.4