Re: [Qemu-devel] 2 issues with qemu-master / 1.2 ehci code

[Hans de Goede]

Hi,

On 08/16/2012 09:26 PM, Gerd Hoffmann wrote:

<snip>

> > I can get things working by turning ehci_fill_queue() into a nop...
> > Investigating this further. But if you've any insights they would be
> > appreciated. I'm thinking this may be caused by packets completing
> > out of order, which could be caused by the special handling of some
> > ctrl commands ...
>
> usbredir wouldn't see multiple parallel inflight requests per endpoint
> unless you explicitly enable this using usb_ep_set_pipeline().  Doing
> that on bulk endpoints should give you a nice performance boost for usb
> sticks.  Doing it on the control endpoint is asking for trouble ;)
>
> Can you turn on all ehci tracepoints & send me a log?

No need for that, I've been debugging this almost the entire day yesterday
and I've significantly narrowed it down further, the problem is that
the assert triggers when:
1) There are more packets then 1 in the queue (iow fill_queue did something)
2) A packet completion is not followed by an advqueue call

2) happens when a packet fails, and the queue should be halted, in this case
ehci_state_writeback() correctly does not call advqueue, bot does a horizqh
instead. The problem is that once this happens p->qtdaddr == q->qtdaddr is no
longer true ...

I've already come up with multiple approaches to try and fix this, but none
work sofar :|


Another problem with failing packets is that hw/usb/core.c will happily execute
the next packet in the ep queue, even though the spec says the ep-queue should
be halted, giving the guest a chance to cancel transfers after the failed one
without them ever executing. I've a poc patch fixing this too.

I've attached a wip patch with my work on this so-far. Note that currently
the halted bit at the ehci level never gets cleared (since we've queues at 2
levels, we need to track halting at 2 levels too)

Regards,

Hans

wip
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