Re: [PATCH v2] [RFC] ehci: Disable wake on overcurrent (WKOC_E) and disconnect (WKDISC_E)

[Ondrej Zary]

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.

It works fine in Windows.

Now I took another machine - IBM ThinkCentre M51 (i915+ICH6). USB ports are 
powered in suspend here so it does not resume immediately. But 
connecting/disconnecting an USB device wakes it up from suspend. Only in 
Linux, not in Windows.

> > > > Does anyone know why is this enabled by default?
> > >
> > > Why _what_ is enabled?  Detection of disconnects?  Because otherwise
> > > your computer wouldn't realize anything had happened when a suspended
> > > USB device was unplugged from a suspended root hub.
> >
> > That's not disconnect detection - that's wakeup on disconnect.
>
> True; I oversimplified.  Furthermore, starting in 2.6.34, the wakeup
> settings during system sleep (suspend or hibernation) can be different
> from the settings during autosuspend, so you can have root hubs enabled
> for wakeup during autosuspend but not during system sleep.
>
> >  If I understand
> > EHCI 1.0 specification correctly, disconnect detection should work
> > regardless
> >
> > of the state of this bit:
> > | PORTSC bit 21: Wake on Disconnect Enable (WKDSCNNT_E):
> > | R/W. Default = 0b.
> > | Writing this bit to a one enables the port to be sensitive to device
> > | disconnects as wake-up events. See Section 4.3 for effects of this bit
> > | on resume event behavior. Refer to Section 4.3.1 for operational model.
> >
> > And it really does. With this patch applied, system does not wake up when
> > a device is disconnected during suspend. When I wake up the system
> > manually, the disconnect is detected immediately (does not matter
>
> It's worth pointing out that EHCI is different in this respect from
> OHCI and UHCI; the older controllers do not have the capability to
> enable or disable wakeup independently for connect, disconnect, and
> overcurrent events.  They are all or nothing.  So are external USB
> hubs.
>
> > > > If we don't need that, perhaps the following patch should be applied.
> > > >
> > > >
> > > > Disable wake on overcurrent and disconnect in EHCI.
> > > > This fixes immediate resume from standby on boards where port power
> > > > is lost in standby which triggers overcurrent detection and
> > > > disconnect if a bus-powered device is connected. At least Asus P4P800
> > > > boards are affected when any of the USBPWxx (e.g. USBPW12) jumpers is
> > > > set to 5V.
> > >
> > > Why would you want to change the jumper settings?  Host controllers are
> > > _supposed_ to supply 5V power during system suspend.
> >
> > Maybe because I don't want all my USB devices to be powered when the
> > system is turned off. I doubt that laptop in suspend-to-RAM (on battery)
> > provides power to USB ports.
>
> This depends on how your system was turned off.  During suspend or
> hibernation, you _should_ want USB devices to be powered (and some
> people do, as Greg pointed out).  During a normal system shutdown, the
> USB buses should not be powered.
>
> 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".

I'm trying to say that the "wakeup on everything" is not a good thing (if not 
a bug). Who needs it? I can't imagine any real use for it. It clearly breaks 
suspend on some systems and is annoying on other. Who expects that 
disconnecting a device should wake up 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).


-- 
Ondrej Zary
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