linux-kernel - [PATCH v2] arm: topology: Consider clock-frequency property from parent /cpus node

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Message-Id: <20221221154213.24382-1-stefan.wiehler@nokia.com>
Date:   Wed, 21 Dec 2022 16:42:13 +0100
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 v2] 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
---
 arch/arm/kernel/topology.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
index ef0058de432b..773c46c07a1c 100644
--- a/arch/arm/kernel/topology.c
+++ b/arch/arm/kernel/topology.c
@@ -90,10 +90,18 @@ static void __init parse_dt_topology(void)
 	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);
 
+	cn = of_find_node_by_path("/cpus");
+	if (!cn)
+		pr_err("missing CPU root device node\n");
+	common_rate = of_get_property(cn, "clock-frequency", &common_rate_len);
+	of_node_put(cn);
+
 	for_each_possible_cpu(cpu) {
 		const __be32 *rate;
 		int len;
@@ -121,8 +129,12 @@ 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;
-- 
2.31.0