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

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Message-Id: <20230426141901.10671-1-stefan.wiehler@nokia.com>
Date:   Wed, 26 Apr 2023 16:19:01 +0200
From:   Stefan Wiehler <stefan.wiehler@...ia.com>
To:     Russell King <linux@...linux.org.uk>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Stefan Wiehler <stefan.wiehler@...ia.com>
Subject: [PATCH v3] arm: topology: Consider clock-frequency property from parent /cpus node

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@...ia.com>
---
- 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