On 31/08/18 02:08 AM, Christian König wrote: >> +One of the biggest issues is that PCI doesn't require forwarding >> +transactions between hierarchy domains, and in PCIe, each Root Port >> +defines a separate hierarchy domain. To make things worse, there is no >> +simple way to determine if a given Root Complex supports this or not. >> +(See PCIe r4.0, sec 1.3.1). Therefore, as of this writing, the kernel >> +only supports doing P2P when the endpoints involved are all behind the >> +same PCI bridge, as such devices are all in the same PCI hierarchy >> +domain, and the spec guarantees that all transacations within the >> +hierarchy will be routable, but it does not require routing >> +between hierarchies. > > Can we add a kernel command line switch and a whitelist to enable P2P > between separate hierarchies? In future work, yes. But not for this patchset. This is definitely the way I see things going, but we've chosen to start with what we've presented. Logan
