linux-kernel - Re: [PATCH 3/3] platform/x86: dell-pc: Transition to faux device

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Message-ID: <2afb6e58-44cb-486e-8062-074ff397dc2c@linux.intel.com>
Date: Wed, 23 Apr 2025 16:27:37 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Kurt Borja <kuurtb@...il.com>, Hans de Goede <hdegoede@...hat.com>, 
    Greg Kroah-Hartman <gregkh@...uxfoundation.org>
cc: Lyndon Sanche <lsanche@...deno.ca>, 
    Mario Limonciello <mario.limonciello@....com>, 
    platform-driver-x86@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] platform/x86: dell-pc: Transition to faux device

On Fri, 11 Apr 2025, Kurt Borja wrote:

> Use a faux device parent for registering the platform_profile instead of
> a "fake" platform device.
> 
> The faux bus is a minimalistic, single driver bus designed for this
> purpose.

Hi Kurt, Hans & Greg,

I'm not sure about this change. So dell-pc not a platform device but
a "fake".

I'm not saying this is wrong, but feel I'm a bit just lost where the 
dividing line is. Is it just because this driver only happens to call
dell_send_request(), etc., not contains that low-level access code within? 
Or is that dell-smbios "fake" too?

> Signed-off-by: Kurt Borja <kuurtb@...il.com>
> ---
>  drivers/platform/x86/dell/dell-pc.c | 46 +++++++++++--------------------------
>  1 file changed, 13 insertions(+), 33 deletions(-)
> 
> diff --git a/drivers/platform/x86/dell/dell-pc.c b/drivers/platform/x86/dell/dell-pc.c
> index 794924913be0c6f13ed4aed8b01ffd21f1d34dea..48cc7511905a62d2828e3a7b593b3d2dae893e34 100644
> --- a/drivers/platform/x86/dell/dell-pc.c
> +++ b/drivers/platform/x86/dell/dell-pc.c
> @@ -13,18 +13,18 @@
>  #include <linux/bitfield.h>
>  #include <linux/bitops.h>
>  #include <linux/bits.h>
> +#include <linux/device/faux.h>
>  #include <linux/dmi.h>
>  #include <linux/err.h>
>  #include <linux/init.h>
>  #include <linux/kernel.h>
>  #include <linux/module.h>
>  #include <linux/platform_profile.h>
> -#include <linux/platform_device.h>
>  #include <linux/slab.h>
>  
>  #include "dell-smbios.h"
>  
> -static struct platform_device *platform_device;
> +static struct faux_device *dell_pc_fdev;
>  static int supported_modes;
>  
>  static const struct dmi_system_id dell_device_table[] __initconst = {
> @@ -246,7 +246,7 @@ static const struct platform_profile_ops dell_pc_platform_profile_ops = {
>  	.profile_set = thermal_platform_profile_set,
>  };
>  
> -static int thermal_init(void)
> +static int dell_pc_faux_probe(struct faux_device *fdev)
>  {
>  	struct device *ppdev;
>  	int ret;
> @@ -258,51 +258,31 @@ static int thermal_init(void)
>  	if (ret < 0)
>  		return ret;
>  
> -	platform_device = platform_device_register_simple("dell-pc", PLATFORM_DEVID_NONE, NULL, 0);
> -	if (IS_ERR(platform_device))
> -		return PTR_ERR(platform_device);
> +	ppdev = devm_platform_profile_register(&fdev->dev, "dell-pc", NULL,
> +					       &dell_pc_platform_profile_ops);
>  
> -	ppdev = devm_platform_profile_register(&platform_device->dev, "dell-pc",
> -					       NULL, &dell_pc_platform_profile_ops);
> -	if (IS_ERR(ppdev)) {
> -		ret = PTR_ERR(ppdev);
> -		goto cleanup_platform_device;
> -	}
> -
> -	return 0;
> -
> -cleanup_platform_device:
> -	platform_device_unregister(platform_device);
> -
> -	return ret;
> +	return PTR_ERR_OR_ZERO(ppdev);
>  }
>  
> -static void thermal_cleanup(void)
> -{
> -	platform_device_unregister(platform_device);
> -}
> +static const struct faux_device_ops dell_pc_faux_ops = {
> +	.probe = dell_pc_faux_probe,
> +};
>  
>  static int __init dell_init(void)
>  {
> -	int ret;
> -
>  	if (!dmi_check_system(dell_device_table))
>  		return -ENODEV;
>  
> -	ret = thermal_init();
> -	if (ret)
> -		goto fail_thermal;
> +	dell_pc_fdev = faux_device_create("dell-pc", NULL, &dell_pc_faux_ops);
> +	if (!dell_pc_fdev)
> +		return -ENODEV;
>  
>  	return 0;
> -
> -fail_thermal:
> -	thermal_cleanup();
> -	return ret;
>  }
>  
>  static void __exit dell_exit(void)
>  {
> -	thermal_cleanup();
> +	faux_device_destroy(dell_pc_fdev);
>  }
>  
>  module_init(dell_init);
> 
> 

-- 
 i.