On 26/03/18 08:01 AM, Bjorn Helgaas wrote: > On Mon, Mar 26, 2018 at 12:11:38PM +0100, Jonathan Cameron wrote: >> On Tue, 13 Mar 2018 10:43:55 -0600 >> Logan Gunthorpe <logang@xxxxxxxxxxxx> wrote: >>> It turns out that root ports that support P2P are far less common than >>> anyone thought. So it will likely have to be a white list. >> >> This came as a bit of a surprise to our PCIe architect. >> >> His follow up was whether it was worth raising an ECR for the PCIe spec >> to add a capability bit to allow this to be discovered. This might >> long term avoid the need to maintain the white list for new devices. >> >> So is it worth having a long term solution for making this discoverable? > > It was surprising to me that there's no architected way to discover > this. It seems like such an obvious thing that I guess I assumed the > omission was intentional, i.e., maybe there's something that makes it > impractical, but it would be worth at least asking somebody in the > SIG. It seems like for root ports in the same root complex, at least, > there could be a bit somewhere in the root port or the RCRB (which > Linux doesn't support yet). Yes, I agree. It would be a good long term solution to have this bit in the spec. That would avoid us needing to create a white list for new hardware. However, I expect it would be years before we can rely on it so someone may yet implement that white list. Logan
