[PATCH v3] arm: topology: Consider clock-frequency property from parent /cpus node

From: Stefan Wiehler
Date: Wed Apr 26 2023 - 10:19:35 EST


If the clock-frequency property is not set in the cpu node but in the
parent /cpus node, the following warning is emitted:

/cpus/cpu@X missing clock-frequency property

The devicetree specification in section 3.8 however specifies that
"properties that have identical values across cpu nodes may be placed in
the /cpus node instead. A client program must first examine a specific cpu
node, but if an expected property is not found then it should look at the
parent /cpus node."

Signed-off-by: Stefan Wiehler <stefan.wiehler@xxxxxxxxx>
---
- Refactored /cpus node lookup
- Add missing node refcount decrement via of_node_put(); of_get_property() does
not need it
- Track lifetime of /cpus node separately
---
arch/arm/kernel/topology.c | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
index ef0058de432b..32fc1c8d9d11 100644
--- a/arch/arm/kernel/topology.c
+++ b/arch/arm/kernel/topology.c
@@ -85,15 +85,24 @@ static bool cap_from_dt = true;
static void __init parse_dt_topology(void)
{
const struct cpu_efficiency *cpu_eff;
- struct device_node *cn = NULL;
+ struct device_node *pcn = NULL, *cn = NULL;
unsigned long min_capacity = ULONG_MAX;
unsigned long max_capacity = 0;
unsigned long capacity = 0;
int cpu = 0;
+ const __be32 *common_rate;
+ int common_rate_len;

__cpu_capacity = kcalloc(nr_cpu_ids, sizeof(*__cpu_capacity),
GFP_NOWAIT);

+ pcn = of_find_node_by_path("/cpus");
+ if (!pcn) {
+ pr_err("missing CPU root device node\n");
+ return;
+ }
+ common_rate = of_get_property(pcn, "clock-frequency", &common_rate_len);
+
for_each_possible_cpu(cpu) {
const __be32 *rate;
int len;
@@ -121,8 +130,12 @@ static void __init parse_dt_topology(void)

rate = of_get_property(cn, "clock-frequency", &len);
if (!rate || len != 4) {
- pr_err("%pOF missing clock-frequency property\n", cn);
- continue;
+ if (common_rate && common_rate_len == 4) {
+ rate = common_rate;
+ } else {
+ pr_err("%pOF missing clock-frequency property\n", cn);
+ continue;
+ }
}

capacity = ((be32_to_cpup(rate)) >> 20) * cpu_eff->efficiency;
@@ -154,6 +167,8 @@ static void __init parse_dt_topology(void)

if (cap_from_dt)
topology_normalize_cpu_scale();
+
+ of_node_put(pcn);
}

/*
--
2.31.0