Re: [Qemu-discuss] Host forwarding requirements.

[shiva.aditham]

Kunal,

 

As you mention, the speed change can be initiated by either side on the link.  However I have seen it being done by the upstream device (in this case the root port) most of the times.  If neither side initiated it, check the training sequences carefully before that to see that both sides advertised that capability.  Cannot recall off hand which field in the trainign sequence indicates the supported speeds.  Please check the PCIe2.0 spec. Not sure why they don't do it all the time, but that is a possibility.   If either side doesn't advertise then the change will not take place.  Or it is quite possible that the speed change was initiated, but didn't complete (have to check traces), in which case they default back to 2.5Gb/s.

 

 

 

> On October 7, 2013 at 2:12 AM dE <address@hidden> wrote:
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> Shiva,
> When both the root port and the endpoint advertise 5 Gbps speed support, wh=
> o responsibility is it to send the TS1s with the speed change bit set? From=
> the spec, I understand that either side can send the speed change TS1, but=
> who is really expected to send it?
> In our setup, we usually see our device send the speed change, however, und=
> er certain conditions we don't and we see that the root port doesn't send i=
> t either. The link is then stuck in 2.5Gbps.
>
> Kunal Shenoy
> System De