linux-kernel - Re: [PATCH v5 07/12] PM / devfreq: export devfreq

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Date:   Wed, 04 Jul 2018 14:30:32 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Matthias Kaehlcke <mka@...omium.org>,
        MyungJoo Ham <myungjoo.ham@...sung.com>
Cc:     Kyungmin Park <kyungmin.park@...sung.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Brian Norris <briannorris@...omium.org>,
        Douglas Anderson <dianders@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Lee Jones <lee.jones@...aro.org>,
        Benson Leung <bleung@...omium.org>,
        Olof Johansson <olof@...om.net>
Subject: Re: [PATCH v5 07/12] PM / devfreq: export devfreq_class

Hi,

I didn't see any framework which exporting the class instance.
It is very dangerous. Unknown device drivers is able to reset
the 'devfreq_class' instance. I can't agree this approach.

Regards,
Chanwoo Choi


On 2018년 07월 04일 08:47, Matthias Kaehlcke wrote:
> Exporting the device class allows other parts of the kernel to enumerate
> the devfreq devices and receive notification when a devfreq device is
> added or removed.
> 
> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> Reviewed-by: Brian Norris <briannorris@...omium.org>
> ---
> Changes in v5:
> - none
> 
> Changes in v4:
> - added 'Reviewed-by: Brian Norris <briannorris@...omium.org>' tag
> 
> Changes in v3:
> - none
> 
> Changes in v2:
> - patch added to series
> ---
>  drivers/devfreq/devfreq.c | 3 ++-
>  include/linux/devfreq.h   | 2 ++
>  2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 4cbaa7ad1972..38b90b64fc6e 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -31,7 +31,8 @@
>  #define MAX(a,b)	((a > b) ? a : b)
>  #define MIN(a,b)	((a < b) ? a : b)
>  
> -static struct class *devfreq_class;
> +struct class *devfreq_class;
> +EXPORT_SYMBOL_GPL(devfreq_class);
>  
>  /*
>   * devfreq core provides delayed work based load monitoring helper
> diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
> index c4f84a769cb5..964e064a951f 100644
> --- a/include/linux/devfreq.h
> +++ b/include/linux/devfreq.h
> @@ -206,6 +206,8 @@ struct devfreq_freqs {
>  };
>  
>  #if defined(CONFIG_PM_DEVFREQ)
> +extern struct class *devfreq_class;
> +
>  extern struct devfreq *devfreq_add_device(struct device *dev,
>  				  struct devfreq_dev_profile *profile,
>  				  const char *governor_name,
>