linux-kernel - [PATCH V2 1/5] cpufreq: acpi: Re-sync CPU boost state on system resume

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Message-Id: <9c7de55fb06015c1b77e7dafd564b659838864e0.1745511526.git.viresh.kumar@linaro.org>
Date: Thu, 24 Apr 2025 21:50:14 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: "Rafael J. Wysocki" <rafael@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Lifeng Zheng <zhenglifeng1@...wei.com>
Cc: linux-pm@...r.kernel.org,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Nicholas Chin <nic.c3.14@...il.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH V2 1/5] cpufreq: acpi: Re-sync CPU boost state on system resume

During CPU hotunplug events (such as those occurring during
suspend/resume cycles), platform firmware may modify the CPU boost
state.

If boost was disabled prior to CPU removal, it correctly remains
disabled upon re-plug. However, if firmware re-enables boost while the
CPU is offline, the CPU may return with boost enabled—even if it was
originally disabled—once it is hotplugged back in. This leads to
inconsistent behavior and violates user or kernel policy expectations.

To maintain consistency, ensure the boost state is re-synchronized with
the kernel policy when a CPU is hotplugged back in.

Note: This re-synchronization is not necessary during the initial call
to ->init() for a CPU, as the cpufreq core handles it via
cpufreq_online(). At that point, acpi_cpufreq_driver.boost_enabled is
initialized to the value returned by boost_state(0).

Fixes: 2b16c631832d ("cpufreq: ACPI: Remove set_boost in acpi_cpufreq_cpu_init()")
Reported-by: Nicholas Chin <nic.c3.14@...il.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220013
Tested-by: Nicholas Chin <nic.c3.14@...il.com>
Reviewed-by: Lifeng Zheng <zhenglifeng1@...wei.com>
Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
 drivers/cpufreq/acpi-cpufreq.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
index 924314cdeebc..d26b610e4f24 100644
--- a/drivers/cpufreq/acpi-cpufreq.c
+++ b/drivers/cpufreq/acpi-cpufreq.c
@@ -909,8 +909,19 @@ static int acpi_cpufreq_cpu_init(struct cpufreq_policy *policy)
 	if (perf->states[0].core_frequency * 1000 != freq_table[0].frequency)
 		pr_warn(FW_WARN "P-state 0 is not max freq\n");

-	if (acpi_cpufreq_driver.set_boost)
-		policy->boost_supported = true;
+	if (acpi_cpufreq_driver.set_boost) {
+		if (policy->boost_supported) {
+			/*
+			 * The firmware may have altered boost state while the
+			 * CPU was offline (for example during a suspend-resume
+			 * cycle).
+			 */
+			if (policy->boost_enabled != boost_state(cpu))
+				set_boost(policy, policy->boost_enabled);
+		} else {
+			policy->boost_supported = true;
+		}
+	}

 	return result;

-- 
2.31.1.272.g89b43f80a514