Re: [PATCH] PM: allow for usage_count > 0 in pm_runtime_get()

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Monday 30 November 2009, Alan Stern wrote:
> This patch (as1308) fixes __pm_runtime_get().  Currently the routine
> will resume a device if the prior usage count was 0.  But this isn't
> right; thanks to pm_runtime_get_noresume() the usage count can be
> positive even while the device is suspended.
> 
> Now the routine always tries to carry out a resume when called
> synchronously.  When called asynchronously, it avoids the overhead of
> an unnecessary spinlock acquisition by doing the resume only if the
> device's state was SUSPENDING or SUSPENDED.
> 
> Signed-off-by: Alan Stern <stern@rowland.harvard.edu>

All three patches applied to suspend-2.6/linux-next.  Do you want me to push
them to Linus before 2.6.32, or perhaps the $subject one only?

Rafael


> ---
> 
> Index: usb-2.6/drivers/base/power/runtime.c
> ===================================================================
> --- usb-2.6.orig/drivers/base/power/runtime.c
> +++ usb-2.6/drivers/base/power/runtime.c
> @@ -703,16 +703,22 @@ EXPORT_SYMBOL_GPL(pm_request_resume);
>   * @dev: Device to handle.
>   * @sync: If set and the device is suspended, resume it synchronously.
>   *
> - * Increment the usage count of the device and if it was zero previously,
> - * resume it or submit a resume request for it, depending on the value of @sync.
> + * Increment the usage count of the device.  If @sync is set, resume the device
> + * and wait for the resume to complete.  Otherwise if the device is currently
> + * suspending or suspended, submit a resume request.
> + *
> + * If @sync is clear, the caller is responsible for synchronization.
>   */
>  int __pm_runtime_get(struct device *dev, bool sync)
>  {
> -	int retval = 1;
> -
> -	if (atomic_add_return(1, &dev->power.usage_count) == 1)
> -		retval = sync ? pm_runtime_resume(dev) : pm_request_resume(dev);
> +	int retval = 0;
>  
> +	atomic_inc(&dev->power.usage_count);
> +	if (sync)
> +		retval = pm_runtime_resume(dev);
> +	else if (dev->power.runtime_status == RPM_SUSPENDING ||
> +	    dev->power.runtime_status == RPM_SUSPENDED)
> +		retval = pm_request_resume(dev);
>  	return retval;
>  }
>  EXPORT_SYMBOL_GPL(__pm_runtime_get);
> Index: usb-2.6/Documentation/power/runtime_pm.txt
> ===================================================================
> --- usb-2.6.orig/Documentation/power/runtime_pm.txt
> +++ usb-2.6/Documentation/power/runtime_pm.txt
> @@ -276,8 +276,9 @@ drivers/base/power/runtime.c and include
>      - increment the device's usage counter
>  
>    int pm_runtime_get(struct device *dev);
> -    - increment the device's usage counter, run pm_request_resume(dev) and
> -      return its result
> +    - increment the device's usage counter; if the device is currently
> +      suspending or suspended then run pm_request_resume(dev) and return its
> +      result
>  
>    int pm_runtime_get_sync(struct device *dev);
>      - increment the device's usage counter, run pm_runtime_resume(dev) and