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From: Beata Michalska <beata.michalska@arm.com>
To: linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	ionela.voinescu@arm.com,
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Subject: [PATCH v3 1/3] arch_topology: init capacity_freq_ref to 0
Date: Tue, 12 Mar 2024 08:34:29 +0000
Message-Id: <20240312083431.3239989-2-beata.michalska@arm.com>
In-Reply-To: <20240312083431.3239989-1-beata.michalska@arm.com>
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From: Ionela Voinescu <ionela.voinescu@arm.com>

It's useful to have capacity_freq_ref initialized to 0 for users of
arch_scale_freq_ref() to detect when capacity_freq_ref was not
yet set.

The only scenario affected by this change in the init value is when a
cpufreq driver is never loaded. As a result, the only setter of a
cpu scale factor remains the call of topology_normalize_cpu_scale()
from parse_dt_topology(). There we cannot use the value 0 of
capacity_freq_ref so we have to compensate for its uninitialized state.

Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
Signed-off-by: Beata Michalska <beata.michalska@arm.com>
---
 drivers/base/arch_topology.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index 024b78a0cfc1..7d4c92cd2bad 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -27,7 +27,7 @@
 static DEFINE_PER_CPU(struct scale_freq_data __rcu *, sft_data);
 static struct cpumask scale_freq_counters_mask;
 static bool scale_freq_invariant;
-DEFINE_PER_CPU(unsigned long, capacity_freq_ref) = 1;
+DEFINE_PER_CPU(unsigned long, capacity_freq_ref) = 0;
 EXPORT_PER_CPU_SYMBOL_GPL(capacity_freq_ref);
 
 static bool supports_scale_freq_counters(const struct cpumask *cpus)
@@ -292,13 +292,15 @@ void topology_normalize_cpu_scale(void)
 
 	capacity_scale = 1;
 	for_each_possible_cpu(cpu) {
-		capacity = raw_capacity[cpu] * per_cpu(capacity_freq_ref, cpu);
+		capacity = raw_capacity[cpu] *
+			   (per_cpu(capacity_freq_ref, cpu) ?: 1);
 		capacity_scale = max(capacity, capacity_scale);
 	}
 
 	pr_debug("cpu_capacity: capacity_scale=%llu\n", capacity_scale);
 	for_each_possible_cpu(cpu) {
-		capacity = raw_capacity[cpu] * per_cpu(capacity_freq_ref, cpu);
+		capacity = raw_capacity[cpu] *
+			   (per_cpu(capacity_freq_ref, cpu) ?: 1);
 		capacity = div64_u64(capacity << SCHED_CAPACITY_SHIFT,
 			capacity_scale);
 		topology_set_cpu_scale(cpu, capacity);
-- 
2.25.1