[PATCH 1/2] cpufreq/amd-pstate: Add an early param to disable MSR mode

[Mario Limonciello <superm1@kernel.org>]

From: Mario Limonciello <mario.limonciello@amd.com>

This lets a system that supports the MSR run in shared memory mode
instead to help replicate and debug issues.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
 .../admin-guide/kernel-parameters.txt         |  5 +++
 Documentation/admin-guide/pm/amd-pstate.rst   |  5 +++
 drivers/cpufreq/amd-pstate.c                  | 32 +++++++++++++------
 3 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 09126bb8cc9ff..041c609ed50ea 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -383,6 +383,11 @@
 			disable
 			  Disable amd-pstate preferred core.
 
+	amd_pstate_msr=
+			[X86]
+			disable
+			  Disable amd-pstate CPPC MSR (force shared memory).
+
 	amijoy.map=	[HW,JOY] Amiga joystick support
 			Map of devices attached to JOY0DAT and JOY1DAT
 			Format: <a>,<b>
diff --git a/Documentation/admin-guide/pm/amd-pstate.rst b/Documentation/admin-guide/pm/amd-pstate.rst
index d0324d44f5482..b06632556102e 100644
--- a/Documentation/admin-guide/pm/amd-pstate.rst
+++ b/Documentation/admin-guide/pm/amd-pstate.rst
@@ -411,6 +411,11 @@ For systems that support ``amd-pstate`` preferred core, the core rankings will
 always be advertised by the platform. But OS can choose to ignore that via the
 kernel parameter ``amd_prefcore=disable``.
 
+``amd_pstate_msr=disable``
+
+For systems that support a dedicated CPPC MSR, ignore it's use and run
+with shared memory instead.
+
 User Space Interface in ``sysfs`` - General
 ===========================================
 
diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 93adde45bebce..89438a3654002 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -88,6 +88,7 @@ static struct cpufreq_driver amd_pstate_epp_driver;
 static int cppc_state = AMD_PSTATE_UNDEFINED;
 static bool cppc_enabled;
 static bool amd_pstate_prefcore = true;
+static bool amd_pstate_msr = true;
 static struct quirk_entry *quirks;
 
 /*
@@ -187,7 +188,7 @@ static s16 amd_pstate_get_epp(struct amd_cpudata *cpudata, u64 cppc_req_cached)
 	u64 epp;
 	int ret;
 
-	if (cpu_feature_enabled(X86_FEATURE_CPPC)) {
+	if (amd_pstate_msr) {
 		if (!cppc_req_cached) {
 			epp = rdmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_REQ,
 					&cppc_req_cached);
@@ -260,7 +261,7 @@ static int amd_pstate_set_epp(struct amd_cpudata *cpudata, u32 epp)
 	int ret;
 	struct cppc_perf_ctrls perf_ctrls;
 
-	if (cpu_feature_enabled(X86_FEATURE_CPPC)) {
+	if (amd_pstate_msr) {
 		u64 value = READ_ONCE(cpudata->cppc_req_cached);
 
 		value &= ~GENMASK_ULL(31, 24);
@@ -813,7 +814,7 @@ static int amd_pstate_get_highest_perf(int cpu, u32 *highest_perf)
 {
 	int ret;
 
-	if (cpu_feature_enabled(X86_FEATURE_CPPC)) {
+	if (amd_pstate_msr) {
 		u64 cap1;
 
 		ret = rdmsrl_safe_on_cpu(cpu, MSR_AMD_CPPC_CAP1, &cap1);
@@ -1058,7 +1059,7 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
 	/* It will be updated by governor */
 	policy->cur = policy->cpuinfo.min_freq;
 
-	if (cpu_feature_enabled(X86_FEATURE_CPPC))
+	if (amd_pstate_msr)
 		policy->fast_switch_possible = true;
 
 	ret = freq_qos_add_request(&policy->constraints, &cpudata->req[0],
@@ -1288,7 +1289,7 @@ static int amd_pstate_change_mode_without_dvr_change(int mode)
 
 	cppc_state = mode;
 
-	if (cpu_feature_enabled(X86_FEATURE_CPPC) || cppc_state == AMD_PSTATE_ACTIVE)
+	if (amd_pstate_msr || cppc_state == AMD_PSTATE_ACTIVE)
 		return 0;
 
 	for_each_present_cpu(cpu) {
@@ -1524,7 +1525,7 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
 	else
 		policy->policy = CPUFREQ_POLICY_POWERSAVE;
 
-	if (cpu_feature_enabled(X86_FEATURE_CPPC)) {
+	if (amd_pstate_msr) {
 		ret = rdmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_REQ, &value);
 		if (ret)
 			return ret;
@@ -1612,7 +1613,7 @@ static void amd_pstate_epp_update_limit(struct cpufreq_policy *policy)
 		epp = 0;
 
 	/* Set initial EPP value */
-	if (cpu_feature_enabled(X86_FEATURE_CPPC)) {
+	if (amd_pstate_msr) {
 		value &= ~GENMASK_ULL(31, 24);
 		value |= (u64)epp << 24;
 	}
@@ -1657,7 +1658,7 @@ static void amd_pstate_epp_reenable(struct amd_cpudata *cpudata)
 	value = READ_ONCE(cpudata->cppc_req_cached);
 	max_perf = READ_ONCE(cpudata->highest_perf);
 
-	if (cpu_feature_enabled(X86_FEATURE_CPPC)) {
+	if (amd_pstate_msr) {
 		wrmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_REQ, value);
 	} else {
 		perf_ctrls.max_perf = max_perf;
@@ -1691,7 +1692,7 @@ static void amd_pstate_epp_offline(struct cpufreq_policy *policy)
 	value = READ_ONCE(cpudata->cppc_req_cached);
 
 	mutex_lock(&amd_pstate_limits_lock);
-	if (cpu_feature_enabled(X86_FEATURE_CPPC)) {
+	if (amd_pstate_msr) {
 		cpudata->epp_policy = CPUFREQ_POLICY_UNKNOWN;
 
 		/* Set max perf same as min perf */
@@ -1936,7 +1937,9 @@ static int __init amd_pstate_init(void)
 	}
 
 	/* capability check */
-	if (cpu_feature_enabled(X86_FEATURE_CPPC)) {
+	if (amd_pstate_msr)
+		amd_pstate_msr = cpu_feature_enabled(X86_FEATURE_CPPC);
+	if (amd_pstate_msr) {
 		pr_debug("AMD CPPC MSR based functionality is supported\n");
 		if (cppc_state != AMD_PSTATE_ACTIVE)
 			current_pstate_driver->adjust_perf = amd_pstate_adjust_perf;
@@ -2002,8 +2005,17 @@ static int __init amd_prefcore_param(char *str)
 	return 0;
 }
 
+static int __init amd_msr_param(char *str)
+{
+	if (!strcmp(str, "disable"))
+		amd_pstate_msr = false;
+
+	return 0;
+}
+
 early_param("amd_pstate", amd_pstate_param);
 early_param("amd_prefcore", amd_prefcore_param);
+early_param("amd_pstate_msr", amd_msr_param);
 
 MODULE_AUTHOR("Huang Rui <ray.huang@amd.com>");
 MODULE_DESCRIPTION("AMD Processor P-state Frequency Driver");
-- 
2.43.0