On Wed, 28 Apr 2010, Ondrej Zary wrote:
> On Wednesday 28 April 2010 17:41:30 Alan Stern wrote:
> > On Tue, 27 Apr 2010, Ondrej Zary wrote:
> > > On Tuesday 27 April 2010 21:21:23 Alan Stern wrote:
> > > > On Tue, 27 Apr 2010, Ondrej Zary wrote:
> > > > > The previous patch was not enough as it worked only when there were
> > > > > no USB devices connected. With a bus-powered device connected, power
> > > > > loss causes disconnect which wakes up the machine immediately again.
> > > >
> > > > You said earlier that the host controller was disabled for remote
> > > > wakeup ("/sys/devices/pci0000:00/0000:00:1d.7/power/wakeup is disabled
> > > > by default"). So even though the root hub might issue a wakeup
> > > > request, the controller hardware should not forward that request to the
> > > > PCI bus and it should not cause the system to wake up.
> > >
> > > Maybe it should not - but it wakes up this board and probably also
> > > P4P800, P4P800-E and P4C800-E at least:
> > > https://bugs.launchpad.net/ubuntu/+source/linux/+bug/75497
> >
> > Okay, evidently the hardware or firmware on these boards is buggy.
> > Other systems do not have the same problem, as far as I know.
I take this back. The same thing happens on my machine (Intel ICH5
chipset). I'd guess there is a bug in the PCI or ACPI subsystem, but
more testing is needed before I can be sure. Somehow the PCI or
platform wakeup mechanism gets activated even when it is supposed to be
disabled.
> It works fine in Windows.
How can you tell? How do you know what values Windows writes into the
EHCI port control registers?
> > Regardless, I don't think a kernel patch is the way to solve your
> > problem. Changing the wakeup setting for the root hub will do what you
> > want, and that setting is explicitly intended to be controlled by
> > userspace (after all, that's why it is exposed in sysfs). The initial
> > value is only a reasonable default; you can certainly add scripts or
> > udev rules to disable wakeup on your EHCI root hub.
>
> Yes, I can work around that. But many users can't. This is an attempt to make
> it "just work".
It should "just work" already. The fact that it doesn't means there is
a bug. At the moment I can't be sure where the bug is -- but even if
it is in ehci-hcd, your suggested patch isn't the right fix.
> I'm trying to say that the "wakeup on everything" is not a good thing (if not
> a bug). Who needs it?
I don't know, and neither do you. But the USB spec requires this
behavior from external hubs, so evidently _somebody_ thought it was a
good idea.
> I can't imagine any real use for it. It clearly breaks
> suspend on some systems and is annoying on other.
If everything was working properly, the machine wouldn't wake up when a
disconnect occurred.
> Who expects that
> disconnecting a device should wake up sleeping machine?
Perhaps the same people who expect that plugging in a device should
wake up a sleeping machine?
> When all these three wakeups (overcurrent, connect, disconnect) are disabled,
> we lose nothing. Connect/disconnect detection works fine after wakeup. Wakeup
> by USB devices (not by connect/disconnect but by the device itself signaling
> a resume) is completely independent of this (according to EHCI
> specification).
What about UHCI or OHCI? What about external hubs?
In short, why should EHCI behave differently from everything else?
Alan Stern
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