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

Peng Fan
2025-04-15T07:58:22Z

On Fri, Apr 11, 2025 at 02:29:41PM -0700, Mike Tipton wrote:
>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@quicinc.com>
>---
> drivers/cpufreq/scmi-cpufreq.c | 29 +++++++++++++++++++++++++++++
> 1 file changed, 29 insertions(+)
>
>diff --git a/drivers/cpufreq/scmi-cpufreq.c b/drivers/cpufreq/scmi-cpufreq.c
>index 944e899eb1be..7981a879974b 100644
>--- a/drivers/cpufreq/scmi-cpufreq.c
>+++ b/drivers/cpufreq/scmi-cpufreq.c
>@@ -393,6 +393,32 @@ 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 = scmi_dev->of_node;
>+ struct device_node *np;
>+ struct device *cpu_dev;
>+ int cpu, idx;
>+
>+ for_each_possible_cpu(cpu) {
>+ cpu_dev = get_cpu_device(cpu);
>+ if (!cpu_dev)
>+ continue;
>+
>+ np = cpu_dev->of_node;
>+
>+ if (of_parse_phandle(np, "clocks", 0) == scmi_np)
>+ return true;
>+
>+ idx = of_property_match_string(np, "power-domain-names", "perf");
>+
>+ if (of_parse_phandle(np, "power-domains", idx) == scmi_np)
>+ return true;
>+ }
>+
>+ return false;
>+}
>+
> static int scmi_cpufreq_probe(struct scmi_device *sdev)
> {
> int ret;
>@@ -404,6 +430,9 @@ static int scmi_cpufreq_probe(struct scmi_device *sdev)
> if (!handle)
> return -ENODEV;
>
>+ if (!scmi_dev_used_by_cpus(dev))
>+ return 0;

Should 'return -ENOTSUPP' be used here?
There is no need to mark the probe success.

Regards,
Peng

>+
> scmi_cpufreq_driver.driver_data = sdev;
>
> perf_ops = handle->devm_protocol_get(sdev, SCMI_PROTOCOL_PERF, &ph);
>--
>2.34.1
>