[PATCH v2] arm64: topology: add source check in arch_cpu_idle_enter()

arch_cpu_idle_enter() directly calls amu_scale_freq_tick() to update
arch_freq_scale when a CPU enters idle. This bypasses the sft_data
pointer check that topology_clear_scale_freq_source() relies on.

As a result, even after calling topology_clear_scale_freq_source()
with SCALE_FREQ_SOURCE_ARCH to disable AMU-based frequency scaling,
the arch_freq_scale value can still be modified by AMU counters when
the CPU goes idle through the arch_cpu_idle_enter() path.

Add topology_scale_freq_source() helper to check whether a specific
frequency scaling source is currently registered for a CPU. Use it
in arch_cpu_idle_enter() to verify that AMU is the active source
before calling amu_scale_freq_tick().

This ensures that topology_clear_scale_freq_source() properly
disables AMU updates in both the tick path (already handled by
topology_scale_freq_tick()) and the idle path.

Co-developed-by: Xuewen Yan <[email protected]>
Signed-off-by: Sean Wang <[email protected]>
Signed-off-by: Xuewen Yan <[email protected]>
---
 arch/arm64/kernel/topology.c  |  3 +++
 drivers/base/arch_topology.c  | 14 ++++++++++++++
 include/linux/arch_topology.h |  1 +
 3 files changed, 18 insertions(+)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index b32f13358fbb..cae5da68d5ec 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -173,6 +173,9 @@ void arch_cpu_idle_enter(void)
 	if (!amu_fie_cpu_supported(cpu))
 		return;
 
+	if (!topology_scale_freq_source(SCALE_FREQ_SOURCE_ARCH, cpu))
+		return;
+
 	/* Kick in AMU update but only if one has not happened already */
 	if (housekeeping_cpu(cpu, HK_TYPE_TICK) &&
 	    time_is_before_jiffies(per_cpu(cpu_amu_samples.last_scale_update, cpu)))
diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index 8c5e47c28d9a..dfc2574a5588 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -127,6 +127,20 @@ void topology_clear_scale_freq_source(enum scale_freq_source source,
 }
 EXPORT_SYMBOL_GPL(topology_clear_scale_freq_source);
 
+bool topology_scale_freq_source(enum scale_freq_source source, unsigned int cpu)
+{
+	struct scale_freq_data *sfd;
+	bool ret;
+
+	rcu_read_lock_sched();
+	sfd = rcu_dereference_sched(*per_cpu_ptr(&sft_data, cpu));
+	ret = (sfd && sfd->source == source);
+	rcu_read_unlock_sched();
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(topology_scale_freq_source);
+
 void topology_scale_freq_tick(void)
 {
 	struct scale_freq_data *sfd = rcu_dereference_sched(*this_cpu_ptr(&sft_data));
diff --git a/include/linux/arch_topology.h b/include/linux/arch_topology.h
index ebd7f8935f96..803382f599a2 100644
--- a/include/linux/arch_topology.h
+++ b/include/linux/arch_topology.h
@@ -48,6 +48,7 @@ struct scale_freq_data {
 void topology_scale_freq_tick(void);
 void topology_set_scale_freq_source(struct scale_freq_data *data, const struct cpumask *cpus);
 void topology_clear_scale_freq_source(enum scale_freq_source source, const struct cpumask *cpus);
+bool topology_scale_freq_source(enum scale_freq_source source, unsigned int cpu);
 
 DECLARE_PER_CPU(unsigned long, hw_pressure);
 
-- 
2.25.1