firmware: arm_scmi: Add fast_switch_possible() interface

Add a new fast_switch_possible interface to the existing perf_ops to
export the information of whether or not fast_switch is possible for a
given device.

This can be used by the cpufreq driver and framework to choose proper
mechanism for frequency change.

Link: https://lore.kernel.org/r/20200617094332.8391-1-nicola.mazzucato@arm.com
Suggested-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Nicola Mazzucato <nicola.mazzucato@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_scmi/perf.c

@@ -697,6 +697,17 @@ static int scmi_dvfs_est_power_get(const struct scmi_handle *handle, u32 domain,
 	return ret;
 }
 
+static bool scmi_fast_switch_possible(const struct scmi_handle *handle,
+				      struct device *dev)
+{
+	struct perf_dom_info *dom;
+	struct scmi_perf_info *pi = handle->perf_priv;
+
+	dom = pi->dom_info + scmi_dev_domain_id(dev);
+
+	return dom->fc_info && dom->fc_info->level_set_addr;
+}
+
 static struct scmi_perf_ops perf_ops = {
 	.limits_set = scmi_perf_limits_set,
 	.limits_get = scmi_perf_limits_get,
@@ -708,6 +719,7 @@ static struct scmi_perf_ops perf_ops = {
 	.freq_set = scmi_dvfs_freq_set,
 	.freq_get = scmi_dvfs_freq_get,
 	.est_power_get = scmi_dvfs_est_power_get,
+	.fast_switch_possible = scmi_fast_switch_possible,
 };
 
 static int scmi_perf_protocol_init(struct scmi_handle *handle)

include/linux/scmi_protocol.h

@@ -118,6 +118,8 @@ struct scmi_perf_ops {
 			unsigned long *rate, bool poll);
 	int (*est_power_get)(const struct scmi_handle *handle, u32 domain,
 			     unsigned long *rate, unsigned long *power);
+	bool (*fast_switch_possible)(const struct scmi_handle *handle,
+				     struct device *dev);
 };
 
 /**