On 2012年11月29日 03:42, Alan Stern wrote:
> 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?
If we do this, I think we should add a flag to record whether the port
has been prevent from power off to avoid pm_runtime_get() more than one
time. Since this function may be invoked many time.
>
> Alan Stern
>
--
Best regards
Tianyu Lan
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