linux-kernel - [PATCH v5 10/11] cpufreq: CPPC: make scaling_min/max_freq read-only when auto

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Message-ID: <20251223121307.711773-11-sumitg@nvidia.com>
Date: Tue, 23 Dec 2025 17:43:06 +0530
From: Sumit Gupta <sumitg@...dia.com>
To: <rafael@...nel.org>, <viresh.kumar@...aro.org>, <lenb@...nel.org>,
	<robert.moore@...el.com>, <corbet@....net>, <pierre.gondois@....com>,
	<zhenglifeng1@...wei.com>, <rdunlap@...radead.org>, <ray.huang@....com>,
	<gautham.shenoy@....com>, <mario.limonciello@....com>, <perry.yuan@....com>,
	<ionela.voinescu@....com>, <zhanjie9@...ilicon.com>,
	<linux-pm@...r.kernel.org>, <linux-acpi@...r.kernel.org>,
	<linux-doc@...r.kernel.org>, <acpica-devel@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>
CC: <linux-tegra@...r.kernel.org>, <treding@...dia.com>,
	<jonathanh@...dia.com>, <vsethi@...dia.com>, <ksitaraman@...dia.com>,
	<sanjayc@...dia.com>, <nhartman@...dia.com>, <bbasu@...dia.com>,
	<sumitg@...dia.com>
Subject: [PATCH v5 10/11] cpufreq: CPPC: make scaling_min/max_freq read-only when auto_sel enabled

When autonomous selection (auto_sel) is enabled, the hardware controls
performance within min_perf/max_perf register bounds making the
scaling_min/max_freq effectively read-only.

Enforce this by setting policy limits to min/max_perf bounds in
cppc_verify_policy(). Users must use min_perf/max_perf sysfs interfaces
to change performance limits in autonomous mode.

Signed-off-by: Sumit Gupta <sumitg@...dia.com>
---
 drivers/cpufreq/cppc_cpufreq.c | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index b1f570d6de34..b3da263c18b0 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -305,7 +305,37 @@ static unsigned int cppc_cpufreq_fast_switch(struct cpufreq_policy *policy,
 
 static int cppc_verify_policy(struct cpufreq_policy_data *policy)
 {
-	cpufreq_verify_within_cpu_limits(policy);
+	unsigned int min_freq = policy->cpuinfo.min_freq;
+	unsigned int max_freq = policy->cpuinfo.max_freq;
+	struct cpufreq_policy *cpu_policy;
+	struct cppc_cpudata *cpu_data;
+	struct cppc_perf_caps *caps;
+
+	cpu_policy = cpufreq_cpu_get(policy->cpu);
+	if (!cpu_policy)
+		return -ENODEV;
+
+	cpu_data = cpu_policy->driver_data;
+	caps = &cpu_data->perf_caps;
+
+	if (cpu_data->perf_ctrls.auto_sel) {
+		u32 min_perf, max_perf;
+
+		/*
+		 * Set policy limits to HW min/max_perf bounds. In autonomous
+		 * mode, scaling_min/max_freq is effectively read-only.
+		 */
+		min_perf = cpu_data->perf_ctrls.min_perf ?:
+			   caps->lowest_nonlinear_perf;
+		max_perf = cpu_data->perf_ctrls.max_perf ?: caps->nominal_perf;
+
+		policy->min = cppc_perf_to_khz(caps, min_perf);
+		policy->max = cppc_perf_to_khz(caps, max_perf);
+	} else {
+		cpufreq_verify_within_limits(policy, min_freq, max_freq);
+	}
+
+	cpufreq_cpu_put(cpu_policy);
 	return 0;
 }
 
-- 
2.34.1