linux-kernel - Re: [RFC PATCH v5 2/4] driver core: Add dev_is_drv_state

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Message-ID: <2023062103-chevron-sabotage-bf26@gregkh>
Date:   Wed, 21 Jun 2023 17:22:54 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Abel Vesa <abel.vesa@...aro.org>
Cc:     "Rafael J . Wysocki" <rafael@...nel.org>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Saravana Kannan <saravanak@...gle.com>,
        Bjorn Andersson <andersson@...nel.org>,
        linux-pm@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm@...r.kernel.org,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Subject: Re: [RFC PATCH v5 2/4] driver core: Add dev_is_drv_state_synced()

On Wed, Jun 21, 2023 at 05:40:17PM +0300, Abel Vesa wrote:
> This can be used by drivers to figure out if a different device
> driver has state synced or not for a specific device.
> 
> Signed-off-by: Abel Vesa <abel.vesa@...aro.org>
> ---
>  include/linux/device.h | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/include/linux/device.h b/include/linux/device.h
> index bae11928ef7e..8f042f04b5d9 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -1007,6 +1007,20 @@ static inline int dev_set_drv_sync_state(struct device *dev,
>  	return 0;
>  }
>  
> +static inline bool dev_is_drv_state_synced(struct device *dev)
> +{
> +	bool ret = false;
> +
> +	if (!dev)
> +		return ret;
> +
> +	device_lock(dev);
> +	ret = dev->state_synced;
> +	device_unlock(dev);

This lock is "protecting" nothing, given that the value can instantly
change after it is read.

Because it can change, how will this function actually show anything
relevant?

thanks,

greg k-h