Re: 2.6.25-rc7: Ugh.

[Mark Lord]

Mark Lord wrote:
> Mark Lord wrote:
> > Mark Lord wrote:
> > > Oliver Neukum wrote:
> > > > Am Montag, 31. MÃrz 2008 17:04:46 schrieb Mark Lord:
> > > > > Oliver Neukum wrote:
> > > > > > Am Montag, 31. MÃrz 2008 16:39:33 schrieb Mark Lord:
> > ..
> > > > > > > Still want USB_SUSPEND=n ?  Please explain.
> > > > > > It looks like you are hanging in the kthread for autosuspending.
> > > > > > Compiling that out should confirm it.
> > > > > ..
> > > > >
> > > > > Okay, and once we see that it works fine:  then what?
> > > >
> > > > We'll combine that information with the result of only removing usbhid
> > > > and arrive at a pretty good idea where in the kernel the hang occurs.
> > > > There are only two functions that touch autosuspend in the usbhid code.
> > > > So if it works with usbhid unloaded, either of them should be to blame.
> > > ..
> > > It does still hang with *usbhid* unloaded,
> > > but not if all USB stuff is unloaded.
> > ..
> >
> > And it does *not* hang with # CONFIG_USB_SUSPEND is not set.
> >
> > > I have figured out a way to make this much more reproducible now:
> > > When suspended, the notebook does not supply +5V over USB.
> > > But with a voltmeter, I discovered that there is sufficient capacitance
> > > on the USB +5V, that it takes many minutes for the voltage to decay
> > > from 5.1V down to near 0V.
> > >
> > > Resuming while the voltage is still relatively high, generally works.
> > > Resuming after the voltage drops to near zero, always fails (with USB 
> > > modules loaded).
> > >
> > > So I've put a 2Kohm resistor across the USB +5V lines,
> > > forcing it to decay to zero within about 5 seconds.
> > > This helps a lot for debugging here.
> > >
> > > It probably also provides a vital clue as to what is wrong.
> > > Resume seems to generally work when the USB devices maintain
> > > some amount of standby power, and always fails when they don't.
> ..
>
> Note that it makes no difference whether I unplug all external USB devices
> prior to suspend or not.  The failure patterns remain the same.
..

I've now removed the internal USB-Bluetooth adaptor, so we can now test
without any USB devices connected.

Suspend without any USB devices plugged-in, and it *always* resumes fine
with working USB, even when the USB stuff is plugged in before hitting
the resume button.

But suspend *with* any USB device plugged-in, and it *always* fails resume,
even when the USB device is unplugged before hitting the resume button.

Conclusion:   the bug is in the usb SUSPEND code, not the RESUME code.
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