From 3872cc6b92940af0f73c6f9a45d65300492d648d Mon Sep 17 00:00:00 2001 From: Oleg Keri Date: Wed, 23 Sep 2026 14:56:04 +0200 Subject: arm64: topology: fix arch_freq_get_on_cpu() overflow above 4.19 GHz arch_freq_get_on_cpu() computes the product of the frequency scale and the reference frequency as a u64, but assigns it to an unsigned int before shifting it back down: freq = scale * arch_scale_freq_ref(cpu); freq >>= SCHED_CAPACITY_SHIFT; The product is truncated to 32 bits before the shift, so the result wraps once arch_scale_freq_ref() exceeds 2^32 / SCHED_CAPACITY_SCALE, i.e. 4194304 kHz. On a Snapdragon X2 Elite (Glymur) laptop, whose boost OPP is 4723200 kHz, cpuinfo_avg_freq reports 524283 kHz instead of ~4723200 kHz while the CPU demonstrably runs at the boost frequency: a fixed workload completes in 1.72 s at the 4723200 kHz OPP versus 2.01 s at 4032000 kHz, matching the 1.171 frequency ratio. Shift the u64 product and narrow only at the return. Fixes: 16d1e27475f6 ("arm64: Provide an AMU-based version of arch_freq_get_on_cpu") Reviewed-by: Dietmar Eggemann Signed-off-by: Oleg Keri Signed-off-by: Will Deacon --- arch/arm64/kernel/topology.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c index d28438f8b..1773dac6f 100644 --- a/arch/arm64/kernel/topology.c +++ b/arch/arm64/kernel/topology.c @@ -186,7 +186,6 @@ int arch_freq_get_on_cpu(int cpu) struct amu_cntr_sample *amu_sample; unsigned int start_cpu = cpu; unsigned long last_update; - unsigned int freq = 0; u64 scale; if (!amu_fie_cpu_supported(cpu) || !arch_scale_freq_ref(cpu)) @@ -245,9 +244,8 @@ int arch_freq_get_on_cpu(int cpu) * (see amu_scale_freq_tick for details) */ scale = arch_scale_freq_capacity(cpu); - freq = scale * arch_scale_freq_ref(cpu); - freq >>= SCHED_CAPACITY_SHIFT; - return freq; + + return (scale * arch_scale_freq_ref(cpu)) >> SCHED_CAPACITY_SHIFT; } static void amu_fie_setup(const struct cpumask *cpus) -- cgit v1.3.1