cpufreq: amd: add fast switch function for amd-pstate

Introduce the fast switch function for amd-pstate on the AMD processors
which support the full MSR register control. It's able to decrease the
lattency on interrupt context.

Signed-off-by: Huang Rui <ray.huang@amd.com>

drivers/cpufreq/amd-pstate.c

@@ -191,6 +191,41 @@ static int amd_pstate_target(struct cpufreq_policy *policy,
 	return 0;
 }
 
+static void amd_pstate_adjust_perf(unsigned int cpu,
+				   unsigned long min_perf,
+				   unsigned long target_perf,
+				   unsigned long capacity)
+{
+	unsigned long amd_max_perf, amd_min_perf, amd_des_perf,
+		      amd_cap_perf, lowest_nonlinear_perf;
+	struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
+	struct amd_cpudata *cpudata = policy->driver_data;
+
+	amd_cap_perf = READ_ONCE(cpudata->highest_perf);
+	lowest_nonlinear_perf = READ_ONCE(cpudata->lowest_nonlinear_perf);
+
+	if (target_perf < capacity)
+		amd_des_perf = DIV_ROUND_UP(amd_cap_perf * target_perf,
+					    capacity);
+
+	amd_min_perf = READ_ONCE(cpudata->highest_perf);
+	if (min_perf < capacity)
+		amd_min_perf = DIV_ROUND_UP(amd_cap_perf * min_perf, capacity);
+
+	if (amd_min_perf < lowest_nonlinear_perf)
+		amd_min_perf = lowest_nonlinear_perf;
+
+	amd_max_perf = amd_cap_perf;
+	if (amd_max_perf < amd_min_perf)
+		amd_max_perf = amd_min_perf;
+
+	amd_des_perf = clamp_t(unsigned long, amd_des_perf,
+			       amd_min_perf, amd_max_perf);
+
+	amd_pstate_update(cpudata, amd_min_perf, amd_des_perf,
+			  amd_max_perf, true);
+}
+
 static int amd_get_min_freq(struct amd_cpudata *cpudata)
 {
 	struct cppc_perf_caps cppc_perf;
@@ -311,6 +346,8 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
 	/* It will be updated by governor */
 	policy->cur = policy->cpuinfo.min_freq;
 
+	policy->fast_switch_possible = true;
+
 	ret = freq_qos_add_request(&policy->constraints, &cpudata->req[0],
 				   FREQ_QOS_MIN, policy->cpuinfo.min_freq);
 	if (ret < 0) {
@@ -360,6 +397,7 @@ static struct cpufreq_driver amd_pstate_driver = {
 	.flags		= CPUFREQ_CONST_LOOPS | CPUFREQ_NEED_UPDATE_LIMITS,
 	.verify		= amd_pstate_verify,
 	.target		= amd_pstate_target,
+	.adjust_perf    = amd_pstate_adjust_perf,
 	.init		= amd_pstate_cpu_init,
 	.exit		= amd_pstate_cpu_exit,
 	.name		= "amd-pstate",