Re: [PATCH 3.12 033/118] usb: xhci: Link TRB must not occur withina USB payload burst [NEW HARDWARE]

From: walt
Date: Sat Jan 18 2014 - 13:34:57 EST

On 01/17/2014 06:34 AM, David Laight wrote:
> From: walt
>> Oy, Sarah! ;) I put the ASMedia adapter in my older amd64 machine, and, well,
>> the stupid thing Just Works(TM) with kernel 3.12.7! (Yes, with the same disk
>> docking station, too.)
>> I can't believe the adapter works perfectly in a different computer. Have you
>> seen this kind of thing before?
> Could be a horrid timing race between the cpu and xchi controller.
> If the cpu manages to write a NOP or LINK TRB for a following transfer
> before the controller polls the next entry (after raising the IRQ)
> then the controller might process the LINK and then get confused
> when it can't process the linked-to TRB.
> This might not sound likely, but PCIe has significant latency.

> Can you try the patch I posted that stops the ownership on LINK TRBs
> being changed before that on the linked-to TRB?

David, the patch doesn't apply cleanly to any 3.12.x sources I can find,
including the latest git from Linus. Half of the hunks fail. Could you
create a fresh patch against vanilla 3.12.8 so I can test it? Or point me
to the correct kernel sources, perhaps.


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