[vfio-users] Bus reset trouble with Titan-X

[Alex Williamson]

On Wed, 19 Oct 2016 11:46:21 -0500
Kevin Vasko <kvasko at gmail.com> wrote:

> Alex,
> 
> Thanks, but no luck.
> 
> I ran :
> 
> #:setpci -s 3:00.0 82.w=8:8
> 
> checked
> 
> #:lspci -vvvs 3:00.0
> 
> MRL- was the same.

PresDet+ on the Changed: line was the thing we were looking for.  MRL
is a retention latch specifically for hotplug capable slots.
 
> #: setpci -s 3:00.0 78.w=20:20
> 
> checked:
> 
> #: lspci -vvs 3:00.0
> 
> MRL- was the same
> 
> 
> LnkSta: Speed 2.5GT/s, Width x0, TrErr- Train- SlotClk- DLActive- BWMgmt-
> ABWMgmt-
> 
> SltSta: Status: AttnBtn- PowerFlt- MRL- CmdCplt- PresDet+ Interlock-
>            Changed: MRL- PresDet+ LinkState-
> 
> Just for my own knowledge what does "retrain" mean? I assume resetting the
> bus and it reconnecting successfully?

Retraining triggers a re-sync of the link width and speed parameters,
think of it like kicking an Ethernet connection to renegotiate
10/100/1000Mbps speeds, a similar thing happens between a device and
the downstream port that it's connected to to determine the link
parameters.  Thanks,

Alex