On Wednesday 02 February 2005 5:35 am, [EMAIL PROTECTED] wrote:
>
> Hi,
> It seems that under some conditions when a usb device is physically
> disconnected and there are some pending urbs ehci_endpoint_disable
> can loop forever in state QH_STATE_UNLINK.
Hmm, that might explain some rare and intermittent problem reports.
What makes you believe that's what's happening?
> I can't really see whether
> this can be a hardware problem or it is purely in software as I don't
> understand the mechanisms involved.
Basic mechanisms:
- If the HC is live:
* For bulk or control endpoints, set up to use the
"Interrupt on Async Advance" (IAA) Doorbell IRQ.
this is what's near the end of ehci-q.c ... basically,
take endpoint's QH off the async ring, arrange for someone
to ring the doorbell.
* For interrupt) endpoints, deschedule the QH and spin
(typically for at most a millisecond) until the host
could no longer be accessing it. (Kind of ugly, but
nice and simple.)
* For isochronous endpoints, just wait till the TDs
(split or otherwise) complete normally, in at most
1024 milliseconds. (Not as ugly, but simpler than
trying to accelerate that unlink.)
- Else the HC is dead; just prcoess all the TDs associated
with that endpoint, there's nobody touching them.
> Can anyone suggest a debugging
> technique? This happens with a clean 2.6.10 kernel.
Have you tried pr_debug() calls in the ehci_endpoint_disable()
logic, and enabling the existing debug output?
It'd be good to use 2.6.11-rc2 instead of 2.6.10, since some
of that code has changed.
> This is triggered by my user space driver calling
> usb_release_interface when it detects a disconnect by a read or write
> to the device failing.
So it could be a case of khubd and your driver competing
on doing the unlink processing...
- Dave
>
> /Brian
>
>
>
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