linux-kernel - RE: [PATCH 3.12 033/118] usb: xhci: Link TRB must not occur within a USB payload burst [NEW HARDWARE]

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Date:	Fri, 17 Jan 2014 14:34:07 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'walt' <w41ter@...il.com>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>
CC:	Alan Stern <stern@...land.harvard.edu>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>
Subject: RE: [PATCH 3.12 033/118] usb: xhci: Link TRB must not occur within
 a USB payload burst [NEW HARDWARE]

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.

> At the moment I have two machines using your xhci driver and both work perfectly,
> so I thank you again :)
> 
> I'm not sure where to go with this next.  I could put the adapter back in the
> other machine again if you have more patches to test.

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

I got a private mail from someone indicating that my earlier 'minimal'
patch helped an ASMedia controller talking to the asx189_178a ethernet
hardware.

	David