On Sat, 17 Nov 2012, Lan Tianyu wrote:

> Some usb devices can't be resumed correctly after power off. This
> patch is to add pm qos flags request to change NO_POWER_OFF and
> provide usb_device_allow_power_off() for device drivers to allow or
> prohibit usb core to power off the device.

What happens if there are two drivers bound to two different 
interfaces, and they both call usb_device_allow_power_off(false), and 
then one of the drivers is unbound and calls 
usb_device_allow_power_off(on)?

Also, instead of using PM QOS flags for this, why not simply have
usb_device_allow_power_off call pm_runtime_{get,put}_sync on the port 
device?

Alan Stern

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