[SRU][N:gke][PATCH 092/106] arm64: Update AMU-based freq scale factor on entering idle

[Tim Whisonant]

From: Beata Michalska <beata.michalska at arm.com>

BugLink: https://bugs.launchpad.net/bugs/2117098

Now that the frequency scale factor has been activated for retrieving
current frequency on a given CPU, trigger its update upon entering
idle. This will, to an extent, allow querying last known frequency
in a non-invasive way. It will also improve the frequency scale factor
accuracy when a CPU entering idle did not receive a tick for a while.
As a consequence, for idle cores, the reported frequency will be the
last one observed before entering the idle state.

Suggested-by: Vanshidhar Konda <vanshikonda at os.amperecomputing.com>
Signed-off-by: Beata Michalska <beata.michalska at arm.com>
Reviewed-by: Prasanna Kumar T S M <ptsm at linux.microsoft.com>
Reviewed-by: Sumit Gupta <sumitg at nvidia.com>
Link: https://lore.kernel.org/r/20250131162439.3843071-5-beata.michalska@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
(cherry picked from commit 39b19974982e03bd7b950f33bc0855385845c9fb)
Signed-off-by: Tim Whisonant <tim.whisonant at canonical.com>
---
 arch/arm64/kernel/topology.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 28fb004d3103c..a09b0551ec59f 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -213,6 +213,19 @@ static __always_inline bool amu_fie_cpu_supported(unsigned int cpu)
 		cpumask_test_cpu(cpu, amu_fie_cpus);
 }
 
+void arch_cpu_idle_enter(void)
+{
+	unsigned int cpu = smp_processor_id();
+
+	if (!amu_fie_cpu_supported(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)))
+		amu_scale_freq_tick();
+}
+
 #define AMU_SAMPLE_EXP_MS	20
 
 int arch_freq_get_on_cpu(int cpu)
-- 
2.43.0