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

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Message-ID: <aBtLMYqcnwacGJuy@pluto>
Date: Wed, 7 May 2025 12:59:45 +0100
From: Cristian Marussi <cristian.marussi@....com>
To: Mike Tipton <quic_mdtipton@...cinc.com>
Cc: Sudeep Holla <sudeep.holla@....com>,
	Cristian Marussi <cristian.marussi@....com>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>, arm-scmi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Peng Fan <peng.fan@....nxp.com>,
	Peng Fan <peng.fan@....com>
Subject: Re: [PATCH v3] cpufreq: scmi: Skip SCMI devices that aren't used by
 the CPUs

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@...cinc.com>
> Reviewed-by: Peng Fan <peng.fan@....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@....com>
Tested-by: Cristian Marussi <cristian.marussi@....com>

Thanks,
Cristian