linux-kernel - Re: [PATCH v8 1/4] device core: add device_is

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Date:	Fri, 02 Oct 2015 15:46:03 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
Cc:	linux-pm@...r.kernel.org, Alan Stern <stern@...land.harvard.edu>,
	martyn.welch@...labora.co.uk, Ulf Hansson <ulf.hansson@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 1/4] device core: add device_is_bound()

On Friday, October 02, 2015 09:14:28 AM Tomeu Vizoso wrote:
> Adds a function that tells whether a device is already bound to a
> driver.
> 
> This is needed to warn when there is an attempt to change the PM domain
> of a device that has finished probing already. The reason why we want to
> enforce that is because in the general case that can cause problems and
> also that we can simplify code quite a bit if we can always assume that.
> 
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
> ---
> 
> Changes in v8:
> - Add device_is_bound()
> 
>  drivers/base/dd.c      | 9 +++++++--
>  include/linux/device.h | 2 ++
>  2 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index be0eb4639128..f2007fa7316f 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -192,9 +192,14 @@ static int deferred_probe_initcall(void)
>  }
>  late_initcall(deferred_probe_initcall);
>  
> +bool device_is_bound(struct device *dev)
> +{
> +	return klist_node_attached(&dev->p->knode_driver);
> +}

It would be useful here to add a comment explaining what locks need to be held
around this for it to be non-racy IMO.

> +
>  static void driver_bound(struct device *dev)
>  {
> -	if (klist_node_attached(&dev->p->knode_driver)) {
> +	if (device_is_bound(dev)) {
>  		printk(KERN_WARNING "%s: device %s already bound\n",
>  			__func__, kobject_name(&dev->kobj));
>  		return;
> @@ -545,7 +550,7 @@ static int __device_attach(struct device *dev, bool allow_async)
>  
>  	device_lock(dev);
>  	if (dev->driver) {
> -		if (klist_node_attached(&dev->p->knode_driver)) {
> +		if (device_is_bound(dev)) {
>  			ret = 1;
>  			goto out_unlock;
>  		}
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 5d7bc6349930..9b41c05fb479 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -1035,6 +1035,8 @@ extern int __must_check driver_attach(struct device_driver *drv);
>  extern void device_initial_probe(struct device *dev);
>  extern int __must_check device_reprobe(struct device *dev);
>  
> +extern bool device_is_bound(struct device *dev);
> +
>  /*
>   * Easy functions for dynamically creating devices on the fly
>   */
> 

Thanks,
Rafael

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