Enabling peer to peer device transactions for PCIe devices

[Logan Gunthorpe]

On 23/10/17 10:08 AM, David Laight wrote:
> It is also worth checking that the hardware actually supports p2p transfers.
> Writes are more likely to be supported then reads.
> ISTR that some intel cpus support some p2p writes, but there could easily
> be errata against them.

Ludwig mentioned a PCIe switch. The few switches I'm aware of support 
P2P transfers. So if everything is setup correctly, the TLPs shouldn't 
even touch the CPU.

But, yes, generally it's a good idea to start with writes and see if 
they work first.

Logan