On Mon, Nov 06, 2017 at 10:11:59AM +0100, Martin Pieuchot wrote:
> On 06/11/17(Mon) 00:24, Paul Irofti wrote:
> > Hi,
> >
> > This is a first step towards hopefully getting uvideo(4) to work with
> > xhci(4). On my x260 I get buffer overrun and my machine freezes when
> > running video(1) with xhci and uvideo debug messages enabled.
> > Following fixes that.
> >
> > The proposed diff handles event under/overruns by dequeueing the current
> > trb from the current segment on the event ring. I think we should do the
> > same for other types of TRBs and that is why I added link support at the
> > end of the dequeueing function.
> >
> > Thoughts? OKs?
>
> Why are we getting under/overruns in the first place? Is the driver
> missing something?
There are multiple problems there that I wanted to talk to you about.
First, without the diff the machine gets caught in an interrupt storm so
something is certainly wrong with the driver. I get
xhci0: slot 3 overrun wih 120 TRB
in an infinite loop and systat confirms the numbers.
Another interesting issue is that the paddr based trb_idx calculation is
also screwed at that point even though we got a proper trb from the
ring.
So I think we are either missing something in xhci_device_isoc_start or
we are not consuming data fast enough.
Anyway, if I am reading the xhci specification correctly, we have to do
at least what my diff proposes when an underrun or overrun event occurs.
