Re: [PATCH 4/4] PCI: Avoid unnecessary resume on shutdown

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On Wednesday, August 31, 2016 08:15:18 AM Lukas Wunner wrote:
> We currently perform a mandatory runtime resume of all PCI devices on
> ->shutdown.  However it is pointless to wake devices only to immediately
> power them down afterwards.  (Or have the firmware reset them, in case
> of a reboot.)
> 
> It seems there are only two cases when a runtime resume is actually
> necessary:  If the driver has declared a ->shutdown callback or if kexec
> is in progress.
> 
> Constrain resume of a device to these cases and let it slumber
> otherwise, thereby conserving energy and speeding up shutdown.
> 
> Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
> ---
>  drivers/pci/pci-driver.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index fd4b9c4..09a4e56 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -459,6 +459,11 @@ static void pci_device_shutdown(struct device *dev)
>  	struct pci_dev *pci_dev = to_pci_dev(dev);
>  	struct pci_driver *drv = pci_dev->driver;
>  
> +	/* Fast path for suspended devices */
> +	if (pm_runtime_suspended(dev) && (!drv || !drv->shutdown) &&
> +	    !kexec_in_progress)

What happens if runtime suspend or resume of the device happens here?

> +		return;
> +
>  	pm_runtime_resume(dev);
>  
>  	if (drv && drv->shutdown)
> 

Thanks,
Rafael

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