On Fri, 23 Dec 2005, Scott D. Davilla wrote:
Disconnect after 6 days, 4 hours. Here's the log. It looks like the
familiar sporadic root hub disconnect. I suspect that there is a
sporadic condition where the root hub indicates a disconnect but the
disconnect is bogus. Can someone explain or give pointers of how the
disconnect is propagated from the ehci hardware to where the hub code
indicates the disconnect. I want to add some debug messages to figure
out if the disconnect occured under a real interrupt from the
hardware or from some watchdog timers or what.
The hub driver periodically queries ehci-hcd to get port status changes.
When the hardware reports a connect status change, the hub driver
processes the change. There aren't any hardware interrupts involved; it's
driven by a kernel timer. But the change notification is genuinely coming
from the hardware.
So you have a periodic kernel timer that triggers a read of the hub
status. Could there be a timing issue where the hub driver is reading
at the wrong time maybe when the status bits are not stable. I've
seen some hardware where you could get a bit glitch when some other
bit is changing. Usually you have to do a double read and look for
same result. Where is the hub status actually read from hardware,
ehci or hub.
The CSC above stands for Connect Status Change. There's no question that
the EHCI hardware detected a connection change. If it was bogus, then
there's a hardware problem.
That's the rub. I'm pretty sure everyone agrees that VIA's ehci
hardware is a little funny. So it seems we get a connect status
change, but it's the root hub glitching. Could it be coming from the
5th and 6th USB ports that are not connected to the outside world.
The VIA chipset has 6 USB ports but only four are brought out, two on
the back plate, two on a header. It makes no difference where we are
connected.
A stack trace (Alt-SysRq-T) showing exactly _where_ the khubd process is
hung would be a big help.
Anyway to pipe this to a log? I've done the stack trace but the
buffers are not big enough to scroll back to khubd.
Scott
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