--- Alan Stern <[EMAIL PROTECTED]> wrote:
> On Mon, 26 Dec 2005, Paul Ionescu wrote:
>
> > Hi Alan,
> >
> > I have a FC4 with kernel 2.6.14-1.1653_FC4, and I wanted to test suspend
> > and even power off a USB device.
> >
> > I plugged a USB flash disk at 3-1 and tried to suspend it:
> > cd /sys/bus/usb/devices
> > echo -n 3 > 3-1/3-1\:1.0/power/state ; echo -n 3 > 3-1/power/state ; echo
> > -n 3 > usb3/power/state
> >
> > While all "state" files changed value to "3", tested with "cat state" in
> > each case, the LED on the usb flash disk is still ON, and I can
> > mount/access it without echoing "0" in the state file.
> > Actually, I don't think that the device is suspended at all.
> > Am I doing something wrong ?
>
> No, but I forgot to mention a very important requirement in my earlier
> message. For this runtime USB power management stuff to work, you _must_
> set the CONFIG_USB_SUSPEND kernel configuration option. And FC4 does not
> set it; so to make things work you will have to rebuild the USB drivers.
OK, I got this one.
> There's one other thing to note: Power off is different from suspend.
> Many USB host controllers are not capable of turning off the power to
> their ports. (All external hubs are supposed to have this capability,
> however.) So if you have a USB device plugged directly into your
> computer, you may indeed be able to suspend it but you probably won't be
> able to power it off.
>
So then, when I "eject" an USB device in M$ Windows, what actually happens is
not a "power off"
the device, but a "suspend" the device ?
Is there any way I can tell if my USB controller is able to power off or not ?
Can it be seen in the output of the lsusb -v ? Or in some /sys files ?
Thanks,
Paul
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