Am Montag 05 Mai 2008 14:45:45 schrieb Alan Jenkins:
> Oliver Neukum wrote:
> > Am Montag 05 Mai 2008 11:51:03 schrieb Alan Jenkins:
> >> drivers isn't considered to require power, then it shouldn't be
> >> considered to be active? Or is this an illogical quirk of the UHCI
> >> hardware?
> >
> > In a way. UHCI needs to do DMA. But many devices crash when suspended.
> > So the kernel refrains from doing so unless told otherwise.
>
> OK. So there could be bad side effects (buggy fingerprint reader starts
> flashing a backlight annoyingly, or kills the bus, or something). Also
Yes.
> if you had a driver but needed to bind it manually / start it in
> userspace, then the kernel would have crashed the device before you
Yes.
> could do anything with it. I had only thought about autosuspend
> breaking devices while you were using them.
>
> >> Are you suggesting that Sascha and others need to identify all the
> >> devices without drivers hanging off their USB bus and de-"activate" them
> >> in sysfs, i.e.
> >>
> >> echo "suspend" > power/level
> >
> > I am suggesting that. Or rather that they use "auto" instead of
> > "suspend"
>
> But if you use "auto", then you have to wait for the timeout (as set in
Yes. 2 seconds by default.
> the autosuspend file), and the driver has to support it to some extent,
Yes. If you have no real kernel driver, usbfs can be considered the driver
for this purpose. It supports autosuspend.
> right? If you can't use the device anyway because there's no driver,
> I'd have thought it's simpler to try forcing it to suspend, rather than
> fiddling with autosuspend.
"suspend" is for desperate cases. It can do bad things if you use the
device. If you break the kernel, you keep the pieces.
> I mentioned earlier that I couldn't get my USB keyboard to autosuspend,
> but I could suspend it manually (on 2.6.24.4). I assume the usb_hid
> driver doesn't support autosuspend. So you're saying autosuspend will
In 2.6.24 it has some extremely rudimentary support that won't work for
keyboards.
> work when there's no driver to veto it (assuming the hardware doesn't
> crash)?
While the device is not in use, yes. A device like a fingerprint reader
will be woken up if user space uses it and suspended again after the
timeout after closure.
I've written better support for autosuspend. It's not fully finished and I've
got reports about deadlocks with keyboards. Do you want to test?
Regards
Oliver
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