Re: [PATCH v3] cpufreq: scmi: Skip SCMI devices that aren't used by the CPUs

Cristian Marussi
2025-05-07T12:03:54Z

On Mon, Apr 28, 2025 at 07:47:28AM -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.
>

Hi,

bit of lagging behind, my bad.

> 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>
> Reviewed-by: Peng Fan <peng.fan@nxp.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 | 31 ++++++++++++++++++++++++++++++-
> 1 file changed, 30 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/cpufreq/scmi-cpufreq.c b/drivers/cpufreq/scmi-cpufreq.c
> index 944e899eb1be..b63992de9fc7 100644
> --- a/drivers/cpufreq/scmi-cpufreq.c
> +++ b/drivers/cpufreq/scmi-cpufreq.c
> @@ -393,6 +393,35 @@ 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 *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;
> +
> + np = dev_of_node(cpu_dev);
> +
> + if (of_parse_phandle(np, "clocks", 0) == scmi_np)

Shouldn't this, on Success, be released by an of_node_put() (or, BETTER,
by some OF-related cleanup.h magic...)

> + return true;
> +
> + idx = of_property_match_string(np, "power-domain-names", "perf");
> +
> + if (of_parse_phandle(np, "power-domains", idx) == scmi_np)

Same.

> + return true;
> + }
> +
> + return false;
> +}
> +
> static int scmi_cpufreq_probe(struct scmi_device *sdev)
> {
> int ret;
> @@ -401,7 +430,7 @@ 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;

Other than the above glitches, LGTM.
(I gave it a go on JUNO and some emulated setup..)

Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Tested-by: Cristian Marussi <cristian.marussi@arm.com>

Thanks,
Cristian