linux-kernel - [PATCH] cpufreq/amd-pstate: Fix setting of CPPC.min_perf in active mode for performance governor

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Message-ID: <20250821042638.356-1-gautham.shenoy@amd.com>
Date: Thu, 21 Aug 2025 09:56:38 +0530
From: "Gautham R. Shenoy" <gautham.shenoy@....com>
To: Mario Limonciello <mario.limonciello@....com>, Perry Yuan
	<perry.yuan@....com>, "Rafael J . Wysocki" <rafael@...nel.org>, Viresh Kumar
	<viresh.kumar@...aro.org>
CC: <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>, "Gautham R.
 Shenoy" <gautham.shenoy@....com>
Subject: [PATCH] cpufreq/amd-pstate: Fix setting of CPPC.min_perf in active mode for performance governor

In the "active" mode of the amd-pstate driver with performance
governor, the CPPC.min_perf is expected to be the nominal_perf.

However after commit a9b9b4c2a4cd ("cpufreq/amd-pstate: Drop min and
max cached frequencies"), this is not the case when the governor is
switched from performance to powersave and back to performance, and
the CPPC.min_perf will be equal to the scaling_min_freq that was set
for the powersave governor.

This is because prior to commit a9b9b4c2a4cd ("cpufreq/amd-pstate:
Drop min and max cached frequencies"), amd_pstate_epp_update_limit()
would unconditionally call amd_pstate_update_min_max_limit() and the
latter function would enforce the CPPC.min_perf constraint when the
governor is performance.

However, after the aforementioned commit,
amd_pstate_update_min_max_limit() is called by
amd_pstate_epp_update_limit() only when either the
scaling_{min/max}_freq is different from the cached value of
cpudata->{min/max}_limit_freq, which wouldn't have changed on a
governor transition from powersave to performance, thus missing out on
enforcing the CPPC.min_perf constraint for the performance governor.

Fix this by invoking amd_pstate_epp_udpate_limit() not only when the
{min/max} limits have changed from the cached values, but also when
the policy itself has changed.

Fixes: a9b9b4c2a4cd ("cpufreq/amd-pstate: Drop min and max cached frequencies")
Signed-off-by: Gautham R. Shenoy <gautham.shenoy@....com>
---
 drivers/cpufreq/amd-pstate.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index f3477ab37742..bbb8e18a6e2b 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -1547,13 +1547,15 @@ static void amd_pstate_epp_cpu_exit(struct cpufreq_policy *policy)
 	pr_debug("CPU %d exiting\n", policy->cpu);
 }

-static int amd_pstate_epp_update_limit(struct cpufreq_policy *policy)
+static int amd_pstate_epp_update_limit(struct cpufreq_policy *policy, bool policy_change)
 {
 	struct amd_cpudata *cpudata = policy->driver_data;
 	union perf_cached perf;
 	u8 epp;

-	if (policy->min != cpudata->min_limit_freq || policy->max != cpudata->max_limit_freq)
+	if (policy_change ||
+	    policy->min != cpudata->min_limit_freq ||
+	    policy->max != cpudata->max_limit_freq)
 		amd_pstate_update_min_max_limit(policy);

 	if (cpudata->policy == CPUFREQ_POLICY_PERFORMANCE)
@@ -1577,7 +1579,7 @@ static int amd_pstate_epp_set_policy(struct cpufreq_policy *policy)

 	cpudata->policy = policy->policy;

-	ret = amd_pstate_epp_update_limit(policy);
+	ret = amd_pstate_epp_update_limit(policy, true);
 	if (ret)
 		return ret;

@@ -1651,7 +1653,7 @@ static int amd_pstate_epp_resume(struct cpufreq_policy *policy)
 		int ret;

 		/* enable amd pstate from suspend state*/
-		ret = amd_pstate_epp_update_limit(policy);
+		ret = amd_pstate_epp_update_limit(policy, false);
 		if (ret)
 			return ret;

-- 
2.34.1