cpufreq/amd-pstate: Add support for the "Requested CPU Min frequency" BIOS option

Initialize lower frequency limit to the "Requested CPU Min frequency"
BIOS option (if it is set) value as part of the driver->init()
callback. The BIOS specified value is passed by the PMFW as min_perf in
CPPC_REQ MSR. To ensure that we don't mistake a stale min_perf value in
CPPC_REQ value as the "Requested CPU Min frequency" during a kexec wakeup,
reset the CPPC_REQ.min_perf value back to the BIOS specified one in the
offline, exit and suspend callbacks.

amd_pstate_target() and amd_pstate_epp_update_limit() which are invoked
as part of the resume() and online() callbacks will take care of restoring
the CPPC_REQ back to the correct values.

Signed-off-by: Dhananjay Ugwekar <dhananjay.ugwekar@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://lore.kernel.org/r/20250428071623.4309-1-dhananjay.ugwekar@amd.com
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>

Author: dhananjay-AMD

drivers/cpufreq/amd-pstate.c

@@ -389,7 +389,8 @@ static inline int amd_pstate_cppc_enable(struct cpufreq_policy *policy)
 static int msr_init_perf(struct amd_cpudata *cpudata)
 {
 	union perf_cached perf = READ_ONCE(cpudata->perf);
-	u64 cap1, numerator;
+	u64 cap1, numerator, cppc_req;
+	u8 min_perf;
 
 	int ret = rdmsrl_safe_on_cpu(cpudata->cpu, MSR_AMD_CPPC_CAP1,
 				     &cap1);
@@ -400,6 +401,22 @@ static int msr_init_perf(struct amd_cpudata *cpudata)
 	if (ret)
 		return ret;
 
+	ret = rdmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_REQ, &cppc_req);
+	if (ret)
+		return ret;
+
+	WRITE_ONCE(cpudata->cppc_req_cached, cppc_req);
+	min_perf = FIELD_GET(AMD_CPPC_MIN_PERF_MASK, cppc_req);
+
+	/*
+	 * Clear out the min_perf part to check if the rest of the MSR is 0, if yes, this is an
+	 * indication that the min_perf value is the one specified through the BIOS option
+	 */
+	cppc_req &= ~(AMD_CPPC_MIN_PERF_MASK);
+
+	if (!cppc_req)
+		perf.bios_min_perf = min_perf;
+
 	perf.highest_perf = numerator;
 	perf.max_limit_perf = numerator;
 	perf.min_limit_perf = FIELD_GET(AMD_CPPC_LOWEST_PERF_MASK, cap1);
@@ -580,20 +597,26 @@ static int amd_pstate_verify(struct cpufreq_policy_data *policy_data)
 {
 	/*
 	 * Initialize lower frequency limit (i.e.policy->min) with
-	 * lowest_nonlinear_frequency which is the most energy efficient
-	 * frequency. Override the initial value set by cpufreq core and
-	 * amd-pstate qos_requests.
+	 * lowest_nonlinear_frequency or the min frequency (if) specified in BIOS,
+	 * Override the initial value set by cpufreq core and amd-pstate qos_requests.
 	 */
 	if (policy_data->min == FREQ_QOS_MIN_DEFAULT_VALUE) {
 		struct cpufreq_policy *policy __free(put_cpufreq_policy) =
 					      cpufreq_cpu_get(policy_data->cpu);
 		struct amd_cpudata *cpudata;
+		union perf_cached perf;
 
 		if (!policy)
 			return -EINVAL;
 
 		cpudata = policy->driver_data;
-		policy_data->min = cpudata->lowest_nonlinear_freq;
+		perf = READ_ONCE(cpudata->perf);
+
+		if (perf.bios_min_perf)
+			policy_data->min = perf_to_freq(perf, cpudata->nominal_freq,
+							perf.bios_min_perf);
+		else
+			policy_data->min = cpudata->lowest_nonlinear_freq;
 	}
 
 	cpufreq_verify_within_cpu_limits(policy_data);
@@ -1024,6 +1047,10 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
 static void amd_pstate_cpu_exit(struct cpufreq_policy *policy)
 {
 	struct amd_cpudata *cpudata = policy->driver_data;
+	union perf_cached perf = READ_ONCE(cpudata->perf);
+
+	/* Reset CPPC_REQ MSR to the BIOS value */
+	amd_pstate_update_perf(policy, perf.bios_min_perf, 0U, 0U, 0U, false);
 
 	freq_qos_remove_request(&cpudata->req[1]);
 	freq_qos_remove_request(&cpudata->req[0]);
@@ -1419,7 +1446,6 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
 	struct amd_cpudata *cpudata;
 	union perf_cached perf;
 	struct device *dev;
-	u64 value;
 	int ret;
 
 	/*
@@ -1484,12 +1510,6 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
 		cpudata->epp_default = AMD_CPPC_EPP_BALANCE_PERFORMANCE;
 	}
 
-	if (cpu_feature_enabled(X86_FEATURE_CPPC)) {
-		ret = rdmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_REQ, &value);
-		if (ret)
-			return ret;
-		WRITE_ONCE(cpudata->cppc_req_cached, value);
-	}
 	ret = amd_pstate_set_epp(policy, cpudata->epp_default);
 	if (ret)
 		return ret;
@@ -1509,6 +1529,11 @@ static void amd_pstate_epp_cpu_exit(struct cpufreq_policy *policy)
 	struct amd_cpudata *cpudata = policy->driver_data;
 
 	if (cpudata) {
+		union perf_cached perf = READ_ONCE(cpudata->perf);
+
+		/* Reset CPPC_REQ MSR to the BIOS value */
+		amd_pstate_update_perf(policy, perf.bios_min_perf, 0U, 0U, 0U, false);
+
 		kfree(cpudata);
 		policy->driver_data = NULL;
 	}
@@ -1566,12 +1591,31 @@ static int amd_pstate_cpu_online(struct cpufreq_policy *policy)
 
 static int amd_pstate_cpu_offline(struct cpufreq_policy *policy)
 {
-	return 0;
+	struct amd_cpudata *cpudata = policy->driver_data;
+	union perf_cached perf = READ_ONCE(cpudata->perf);
+
+	/*
+	 * Reset CPPC_REQ MSR to the BIOS value, this will allow us to retain the BIOS specified
+	 * min_perf value across kexec reboots. If this CPU is just onlined normally after this, the
+	 * limits, epp and desired perf will get reset to the cached values in cpudata struct
+	 */
+	return amd_pstate_update_perf(policy, perf.bios_min_perf, 0U, 0U, 0U, false);
 }
 
 static int amd_pstate_suspend(struct cpufreq_policy *policy)
 {
 	struct amd_cpudata *cpudata = policy->driver_data;
+	union perf_cached perf = READ_ONCE(cpudata->perf);
+	int ret;
+
+	/*
+	 * Reset CPPC_REQ MSR to the BIOS value, this will allow us to retain the BIOS specified
+	 * min_perf value across kexec reboots. If this CPU is just resumed back without kexec,
+	 * the limits, epp and desired perf will get reset to the cached values in cpudata struct
+	 */
+	ret = amd_pstate_update_perf(policy, perf.bios_min_perf, 0U, 0U, 0U, false);
+	if (ret)
+		return ret;
 
 	/* invalidate to ensure it's rewritten during resume */
 	cpudata->cppc_req_cached = 0;
@@ -1582,6 +1626,17 @@ static int amd_pstate_suspend(struct cpufreq_policy *policy)
 	return 0;
 }
 
+static int amd_pstate_resume(struct cpufreq_policy *policy)
+{
+	struct amd_cpudata *cpudata = policy->driver_data;
+	union perf_cached perf = READ_ONCE(cpudata->perf);
+	int cur_perf = freq_to_perf(perf, cpudata->nominal_freq, policy->cur);
+
+	/* Set CPPC_REQ to last sane value until the governor updates it */
+	return amd_pstate_update_perf(policy, perf.min_limit_perf, cur_perf, perf.max_limit_perf,
+				      0U, false);
+}
+
 static int amd_pstate_epp_resume(struct cpufreq_policy *policy)
 {
 	struct amd_cpudata *cpudata = policy->driver_data;
@@ -1610,6 +1665,7 @@ static struct cpufreq_driver amd_pstate_driver = {
 	.online		= amd_pstate_cpu_online,
 	.offline	= amd_pstate_cpu_offline,
 	.suspend	= amd_pstate_suspend,
+	.resume		= amd_pstate_resume,
 	.set_boost	= amd_pstate_set_boost,
 	.update_limits	= amd_pstate_update_limits,
 	.name		= "amd-pstate",

drivers/cpufreq/amd-pstate.h

@@ -30,6 +30,7 @@
  * @lowest_perf: the absolute lowest performance level of the processor
  * @min_limit_perf: Cached value of the performance corresponding to policy->min
  * @max_limit_perf: Cached value of the performance corresponding to policy->max
+ * @bios_min_perf: Cached perf value corresponding to the "Requested CPU Min Frequency" BIOS option
  */
 union perf_cached {
 	struct {
@@ -39,6 +40,7 @@ union perf_cached {
 		u8	lowest_perf;
 		u8	min_limit_perf;
 		u8	max_limit_perf;
+		u8	bios_min_perf;
 	};
 	u64	val;
 };