Re: [Libusb-devel] A new request for libusb_event_t

[Alan S. <st...@ro...>]

On Thu, 14 Jul 2011, Xiaofan Chen wrote:

> On Tue, Jul 12, 2011 at 11:39 PM, Alan Stern <st...@ro...> wrote:
> > On Tue, 12 Jul 2011, Xiaofan Chen wrote:
> >
> >> On Mon, May 21, 2007 at 5:36 PM, Gaopeng Chen - Sun China
> >> <Gao...@su...> wrote:
> >> > Hi all,
> >> >
> >> > Is it possible to export two new events for libusb_event_t?
> >> >
> >> > USB_SUSPEND
> >> > USB_RESUME
> >> >
> >> > I'm working on a fingerprint device, which supports advanced power
> >> > management. Users can send a control msg to suspend the device. Once a
> >> > finger is pressed, the device will wake up and resume. Thus the resume
> >> > event is required to be issued. I think this is very useful for USB
> >> > devices that's required to be power saved and remote wake-up.
> >>
> >> This is an old thread.
> >> http://libusb.6.n5.nabble.com/A-new-request-for-libusb-event-t-td2992.html
> >>
> >> The thread seems to suggest that the above is possible under
> >> Linux and Solaris.
> >>
> >> How to support this under Linux? Is it possible to do similar
> >> things for Windows and Mac OS X?
> >
> > It's currently not possible under Linux. No event notifications are
> > sent to userspace when a device is suspended or resumed. Reference
> > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=drivers/usb/core/devio.c
> > lines 506-517; the usbfs suspend and resume routines don't do anything.
> > Of course it is theoretically possible to add such notifications, but
> > they don't exist now.
> >
> > The message in that earlier thread (which seemed to suggest this was
> > possible) was wrong. The person who wrote the message misunderstood
> > the code.
> 
> Thanks for the clarification.
> 
> Interestingly it can be done under FreeBSD 8.x.
> http://www.unix.com/man-page/FreeBSD/3/libusb20/
>      libusb20_dev_set_power_mode() sets the power mode of the USB device.
>      Valid power modes:
>      LIBUSB20_POWER_OFF
>      LIBUSB20_POWER_ON
>      LIBUSB20_POWER_SAVE
>      LIBUSB20_POWER_SUSPEND
>      LIBUSB20_POWER_RESUME
> 
> Under Windows, winusb has some power policy as well.
> http://msdn.microsoft.com/en-us/library/ff540309%28v=vs.85%29.aspx
> http://msdn.microsoft.com/en-us/library/ff728834%28v=vs.85%29.aspx
> 
> I do not know about Mac OS X but it seems to be possible as well.
> http://developer.apple.com/library/mac/#documentation/DeviceDrivers/Conceptual/IOKitFundamentals/PowerMgmt/PowerMgmt.html#//apple_ref/doc/uid/TP0000020-BABCCBIJ
> 
> So it might be good for Linux to have similar things as well.

They could be added as well.  But changing a device's power state is 
different from getting notifications about power-state changes.

Alan Stern