linux-kernel - Re: [PATCH v2 2/8] cpuidle: psci: Transition to the faux device interface

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Message-ID: <2025041515-duplex-recant-7235@gregkh>
Date: Tue, 15 Apr 2025 14:21:33 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Sudeep Holla <sudeep.holla@....com>
Cc: linux-kernel@...r.kernel.org, Lorenzo Pieralisi <lpieralisi@...nel.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH v2 2/8] cpuidle: psci: Transition to the faux device
 interface

On Tue, Mar 18, 2025 at 05:01:40PM +0000, Sudeep Holla wrote:
> The PSCI cpuidle driver does not require the creation of a platform
> device. Originally, this approach was chosen for simplicity when the
> driver was first implemented.
> 
> With the introduction of the lightweight faux device interface, we now
> have a more appropriate alternative. Migrate the driver to utilize the
> faux bus, given that the platform device it previously created was not
> a real one anyway. This will simplify the code, reducing its footprint
> while maintaining functionality.
> 
> Cc: Lorenzo Pieralisi <lpieralisi@...nel.org>
> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
> Cc: linux-pm@...r.kernel.org
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> ---
>  drivers/cpuidle/cpuidle-psci.c | 32 ++++----------------------------
>  1 file changed, 4 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c
> index 2562dc001fc1de69732ef28f383d2809262a3d96..5d4d6daed36d8540ba2ce3dc54a3180731b03d22 100644
> --- a/drivers/cpuidle/cpuidle-psci.c
> +++ b/drivers/cpuidle/cpuidle-psci.c
> @@ -16,7 +16,7 @@
>  #include <linux/kernel.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
> -#include <linux/platform_device.h>
> +#include <linux/device/faux.h>
>  #include <linux/psci.h>
>  #include <linux/pm_domain.h>
>  #include <linux/pm_runtime.h>
> @@ -404,14 +404,14 @@ static int psci_idle_init_cpu(struct device *dev, int cpu)
>   * to register cpuidle driver then rollback to cancel all CPUs
>   * registration.
>   */
> -static int psci_cpuidle_probe(struct platform_device *pdev)
> +static int psci_cpuidle_probe(struct faux_device *fdev)
>  {
>  	int cpu, ret;
>  	struct cpuidle_driver *drv;
>  	struct cpuidle_device *dev;
>  
>  	for_each_possible_cpu(cpu) {
> -		ret = psci_idle_init_cpu(&pdev->dev, cpu);
> +		ret = psci_idle_init_cpu(&fdev->dev, cpu);
>  		if (ret)
>  			goto out_fail;
>  	}
> @@ -431,28 +431,4 @@ static int psci_cpuidle_probe(struct platform_device *pdev)
>  	return ret;
>  }
>  
> -static struct platform_driver psci_cpuidle_driver = {
> -	.probe = psci_cpuidle_probe,
> -	.driver = {
> -		.name = "psci-cpuidle",
> -	},
> -};
> -
> -static int __init psci_idle_init(void)
> -{
> -	struct platform_device *pdev;
> -	int ret;
> -
> -	ret = platform_driver_register(&psci_cpuidle_driver);
> -	if (ret)
> -		return ret;
> -
> -	pdev = platform_device_register_simple("psci-cpuidle", -1, NULL, 0);
> -	if (IS_ERR(pdev)) {
> -		platform_driver_unregister(&psci_cpuidle_driver);
> -		return PTR_ERR(pdev);
> -	}
> -
> -	return 0;
> -}
> -device_initcall(psci_idle_init);
> +module_faux_driver(psci_cpuidle, psci_cpuidle_probe, NULL, true);

See, what does "true" mean here?

Why would you ever want "false"?

thanks,

greg k-h