[PATCH v4] cpufreq: scmi: Skip SCMI devices that aren't used by the CPUs

[Mike Tipton]

Currently, all SCMI devices with performance domains attempt to register
a cpufreq driver, even if their performance domains aren't used to
control the CPUs. The cpufreq framework only supports registering a
single driver, so only the first device will succeed. And if that device
isn't used for the CPUs, then cpufreq will scale the wrong domains.

To avoid this, return early from scmi_cpufreq_probe() if the probing
SCMI device isn't referenced by the CPU device phandles.

This keeps the existing assumption that all CPUs are controlled by a
single SCMI device.

Signed-off-by: Mike Tipton <quic_mdtipton at quicinc.com>
Reviewed-by: Peng Fan <peng.fan at nxp.com>
Reviewed-by: Cristian Marussi <cristian.marussi at arm.com>
Reviewed-by: Sudeep Holla <sudeep.holla at arm.com>
Tested-by: Cristian Marussi <cristian.marussi at arm.com>
---
Changes in v4:
- Call of_node_put() after of_parse_handle().
- Collect Reviewed-bys and Tested-bys.
- Link to v3: https://lore.kernel.org/all/20250428144728.871404-1-quic_mdtipton@quicinc.com/

Changes in v3:
- Use dev_of_node(dev) instead of dev->of_node.
- Sanity check scmi_np.
- Pick up Reviewed-by from Peng.
- Link to v2: https://lore.kernel.org/all/20250421195206.3736128-1-quic_mdtipton@quicinc.com/

Changes in v2:
- Return -ENODEV instead of 0 for irrelevant devices.
- Link to v1: https://lore.kernel.org/all/20250411212941.1275572-1-quic_mdtipton@quicinc.com/

 drivers/cpufreq/scmi-cpufreq.c | 36 +++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/scmi-cpufreq.c b/drivers/cpufreq/scmi-cpufreq.c
index 944e899eb1be..ef078426bfd5 100644
--- a/drivers/cpufreq/scmi-cpufreq.c
+++ b/drivers/cpufreq/scmi-cpufreq.c
@@ -393,6 +393,40 @@ static struct cpufreq_driver scmi_cpufreq_driver = {
 	.set_boost	= cpufreq_boost_set_sw,
 };
 
+static bool scmi_dev_used_by_cpus(struct device *scmi_dev)
+{
+	struct device_node *scmi_np = dev_of_node(scmi_dev);
+	struct device_node *cpu_np, *np;
+	struct device *cpu_dev;
+	int cpu, idx;
+
+	if (!scmi_np)
+		return false;
+
+	for_each_possible_cpu(cpu) {
+		cpu_dev = get_cpu_device(cpu);
+		if (!cpu_dev)
+			continue;
+
+		cpu_np = dev_of_node(cpu_dev);
+
+		np = of_parse_phandle(cpu_np, "clocks", 0);
+		of_node_put(np);
+
+		if (np == scmi_np)
+			return true;
+
+		idx = of_property_match_string(cpu_np, "power-domain-names", "perf");
+		np = of_parse_phandle(cpu_np, "power-domains", idx);
+		of_node_put(np);
+
+		if (np == scmi_np)
+			return true;
+	}
+
+	return false;
+}
+
 static int scmi_cpufreq_probe(struct scmi_device *sdev)
 {
 	int ret;
@@ -401,7 +435,7 @@ static int scmi_cpufreq_probe(struct scmi_device *sdev)
 
 	handle = sdev->handle;
 
-	if (!handle)
+	if (!handle || !scmi_dev_used_by_cpus(dev))
 		return -ENODEV;
 
 	scmi_cpufreq_driver.driver_data = sdev;
-- 
2.34.1