On Fri, Sep 21, 2012 at 11:36:37AM +0800, Lan Tianyu wrote: > On 2012年09月21日 09:52, Peter Chen wrote: > >> > >> Where I would like to see this work go is to have a certain set of > >> "safe" internal USB devices be powered off by default when they are > >> suspended. I think fingerprint readers and webcams would be a good > >> start, but we probably can't do bluetooth, 3G modems, BMCs, etc. We > >> would need a new USB driver flag to allow drivers to opt-in to the > >> automatic port power off on suspend. We should probably turn that on by > >> default and see if anyone has issues. > >> > > > > If I understand correctly, only below ports can be power off compared current's. > > > > - The internal port which is not connected any devices > > - The internal port which is connected non remote-wakeup featured > > device, and the port power can be off through user space application > > - any other ports? > > > > For fingerprint, how can we let it re-use? Unless there is another > > interrupt to indicate > > when we touch it or other things? > > If the device needed outside event, the remote-wakeup would not be > disabled and so the device would not be power off. Tianyu is correct. Fingerprint readers don't have remote wakeup capabilities, so they don't send an interrupt when they scan a finger. Instead, a userspace program claims the interface via usbfs and reads from the device when it wants to capture a finger scan. The kernel's "auto" power policy would turn back on the port as soon as the interface was claimed through usbfs. Sarah Sharp -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
