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: linux...@vger.kernel.org
Acked-by: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
Acked-by: Viresh Kumar <viresh.ku...@linaro.org>
Signed-off-by: Sudeep Holla <sudeep.ho...@arm.com>
---
 drivers/cpufreq/scmi-cpufreq.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/cpufreq/scmi-cpufreq.c b/drivers/cpufreq/scmi-cpufreq.c
index d6d35f7692b3..c869c99b2142 100644
--- a/drivers/cpufreq/scmi-cpufreq.c
+++ b/drivers/cpufreq/scmi-cpufreq.c
@@ -64,6 +64,19 @@ scmi_cpufreq_set_target(struct cpufreq_policy *policy, 
unsigned int index)
        return perf_ops->freq_set(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 = handle->perf_ops;
+
+       if (!perf_ops->freq_set(handle, priv->domain_id,
+                               target_freq * 1000, true))
+               return target_freq;
+
+       return 0;
+}
+
 static int
 scmi_get_sharing_cpus(struct device *cpu_dev, struct cpumask *cpumask)
 {
@@ -163,6 +176,7 @@ 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:
@@ -201,6 +215,7 @@ static struct cpufreq_driver scmi_cpufreq_driver = {
        .verify = cpufreq_generic_frequency_table_verify,
        .attr   = cpufreq_generic_attr,
        .target_index   = scmi_cpufreq_set_target,
+       .fast_switch    = scmi_cpufreq_fast_switch,
        .get    = scmi_cpufreq_get_rate,
        .init   = scmi_cpufreq_init,
        .exit   = scmi_cpufreq_exit,
-- 
2.7.4

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