linux-kernel - Re: [PATCH] ACPI: processor: Add acpi_processor_start() back to parse

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Message-ID: <CAJZ5v0hX839+J-MdKUwpRv0D9HSj-sbtMN0o-OOYatu9dU+bFQ@mail.gmail.com>
Date: Tue, 27 Jan 2026 15:42:16 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Lifeng Zheng <zhenglifeng1@...wei.com>, jonathan.cameron@...wei.com
Cc: catalin.marinas@....com, linux-acpi@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linuxarm@...wei.com, gshan@...hat.com, 
	miguel.luis@...cle.com, guohanjun@...wei.com, zhanjie9@...ilicon.com, 
	lihuisong@...wei.com, yubowen8@...wei.com, zhangpengjie2@...wei.com, 
	wangzhi12@...wei.com, linhongye@...artners.com
Subject: Re: [PATCH] ACPI: processor: Add acpi_processor_start() back to parse
 _CPC tables before CPU online

On Tue, Jan 20, 2026 at 12:33 PM Lifeng Zheng <zhenglifeng1@...wei.com> wrote:
>
> Currently, if boot with maxcpus less than NR_CPUS, the cppc_cpufreq driver
> will fail to register. Because it requires the domain information of all
> possible CPUs to construct shared_cpu_map, which shows the CPUs that share
> the same domain.
>
> Commit c1385c1f0ba3 ("ACPI: processor: Simplify initial onlining to use
> same path for cold and hotplug") removes probe() of acpi_processor_driver
> and makes acpi_cppc_processor_probe() only being called the first time CPU
> goes online. This means that CPUs that haven't yet gone online will not
> have pre-parsed _CPC objects and causes cppc_cpufreq driver register fail.
>
> Add acpi_processor_start() back as the probe() callback of
> acpi_processor_driver and call acpi_cppc_processor_probe() in it to make
> sure all _CPC tables will be parsed when acpi_processor_driver registered.
>
> Fixes: c1385c1f0ba3 ("ACPI: processor: Simplify initial onlining to use same path for cold and hotplug")
> Signed-off-by: Lifeng Zheng <zhenglifeng1@...wei.com>
> ---
>  drivers/acpi/processor_driver.c | 30 ++++++++++++++++++++++++++----
>  1 file changed, 26 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/acpi/processor_driver.c b/drivers/acpi/processor_driver.c
> index 65e779be64ff..c8b4daf580b0 100644
> --- a/drivers/acpi/processor_driver.c
> +++ b/drivers/acpi/processor_driver.c
> @@ -33,6 +33,7 @@ MODULE_AUTHOR("Paul Diefenbaugh");
>  MODULE_DESCRIPTION("ACPI Processor Driver");
>  MODULE_LICENSE("GPL");
>
> +static int acpi_processor_start(struct device *dev);
>  static int acpi_processor_stop(struct device *dev);
>
>  static const struct acpi_device_id processor_device_ids[] = {
> @@ -46,6 +47,7 @@ static struct device_driver acpi_processor_driver = {
>         .name = "processor",
>         .bus = &cpu_subsys,
>         .acpi_match_table = processor_device_ids,
> +       .probe = acpi_processor_start,
>         .remove = acpi_processor_stop,
>  };
>
> @@ -162,10 +164,6 @@ static int __acpi_processor_start(struct acpi_device *device)
>         if (!pr)
>                 return -ENODEV;
>
> -       result = acpi_cppc_processor_probe(pr);
> -       if (result && !IS_ENABLED(CONFIG_ACPI_CPU_FREQ_PSS))
> -               dev_dbg(&device->dev, "CPPC data invalid or not present\n");
> -
>         if (!cpuidle_get_driver() || cpuidle_get_driver() == &acpi_idle_driver)
>                 acpi_processor_power_init(pr);
>
> @@ -192,6 +190,30 @@ static int __acpi_processor_start(struct acpi_device *device)
>         return result;
>  }
>
> +static int acpi_processor_start(struct device *dev)
> +{
> +       struct acpi_device *device = ACPI_COMPANION(dev);
> +       struct acpi_processor *pr;
> +       int result;
> +
> +       if (!device)
> +               return -ENODEV;
> +
> +       pr = acpi_driver_data(device);
> +       if (!pr)
> +               return -ENODEV;
> +
> +       /* Protect against concurrent CPU hotplug operations */
> +       cpu_hotplug_disable();
> +       result = acpi_cppc_processor_probe(pr);
> +       cpu_hotplug_enable();

This means that CPPC will be initialized for vCPUs that are not
enabled on ARM if I'm not mistaken.

I'm not sure if it is valid to do so.

Jonathan?

> +
> +       if (result && !IS_ENABLED(CONFIG_ACPI_CPU_FREQ_PSS))
> +               dev_dbg(&device->dev, "CPPC data invalid or not present\n");
> +
> +       return 0;
> +}
> +
>  static int acpi_processor_stop(struct device *dev)
>  {
>         struct acpi_device *device = ACPI_COMPANION(dev);
> --
> 2.33.0
>
>