linux-kernel - Re: [BUGFIX 2/4] PCI/PM: Keep parent bridge active when probing device

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Date:	Sat, 4 Aug 2012 23:48:08 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Huang Ying <ying.huang@...el.com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [BUGFIX 2/4] PCI/PM: Keep parent bridge active when probing device

On Friday, August 03, 2012, Huang Ying wrote:
> This patch fixes the following bug:
> 
> http://marc.info/?l=linux-pci&m=134329923124234&w=2
> 
> The root cause of the bug is as follow.
> 
> If a device is not bound with the corresponding driver, the device
> runtime PM will be disabled and the device will be put into suspended
> state.  So that, the bridge/PCIe port connected to it may be put into
> suspended and low power state.  When do probing for the device later,
> because the bridge/PCIe port connected to it is in low power state,
> the IO access to device may fail.
> 
> To solve the issue, the bridge/PCIe port connected to the device is
> put into active state before probing.
> 
> Reported-by: Bjorn Mork <bjorn@...k.no>
> Signed-off-by: Huang Ying <ying.huang@...el.com>

Reviewed-by: Rafael J. Wysocki <rjw@...k.pl>

> ---
>  drivers/pci/pci-driver.c |    6 ++++++
>  1 file changed, 6 insertions(+)
> 
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -280,8 +280,12 @@ static long local_pci_probe(void *_ddi)
>  {
>  	struct drv_dev_and_id *ddi = _ddi;
>  	struct device *dev = &ddi->dev->dev;
> +	struct device *parent = dev->parent;
>  	int rc;
>  
> +	/* The parent bridge must be in active state when probing */
> +	if (parent)
> +		pm_runtime_get_sync(parent);
>  	/* Unbound PCI devices are always set to disabled and suspended.
>  	 * During probe, the device is set to enabled and active and the
>  	 * usage count is incremented.  If the driver supports runtime PM,
> @@ -298,6 +302,8 @@ static long local_pci_probe(void *_ddi)
>  		pm_runtime_set_suspended(dev);
>  		pm_runtime_put_noidle(dev);
>  	}
> +	if (parent)
> +		pm_runtime_put(parent);
>  	return rc;
>  }
>  
> 
> 

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