On Fri, 9 Nov 2012, Lan Tianyu wrote:

> This patch is to add usb port auto power off mechanism.
> When usb device is suspending, usb core will send clear usb port's
> POWER feature requst to power off port if all conditions were met.

Actually, this is the wrong approach.

What you should do, if all the conditions are met, is call 
pm_runtime_put(&port_dev->dev).  Then the port's runtime suspend 
routine should be responsible for turning off the power.

Similarly, whenever you want to make sure that a port is powered, you 
should call pm_runtime_get_sync(&port_dev->dev).

Alan Stern

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