On 2021-06-10 4:05 p.m., Bjorn Helgaas wrote: > The new text is: > > If there are two virtual functions of the same device behind the same > bridge port then PCI_P2PDMA_MAP_BUS_ADDR and a distance of 2 will be > returned (one step down to the PCIe switch, then one step back to the > same device). > > I *think* this includes two functions of the same multi-function > device, or two virtual functions of the same device, right? In both > cases, the two devices are obviously behind the same bridge port. Yes, that's correct, if it's the same device it must be behind the same bridge port; so dropping the "behind the same bridge port" is a good idea. > > Is this usage of "down to the PCIe switch" the common usage in P2PDMA? > I normally think of going from an endpoint to a switch as being "up" > toward the CPU. But PCIe made it all confusing by putting downstream > ports at the upstream end of links and vice versa. Good point. I've been casually saying "down to", but you are right "up" makes a lot more sense given the downstream/upstream terminology. > We also have a bit of a mix in terminology between "bridge," "switch," > "bridge port." I'd probably write something like: > > If they are two functions of the same device behind the same bridge, > return PCI_P2PDMA_MAP_BUS_ADDR and a distance of 2 (one hop up to > the bridge, then one hop back down to another function of the same > device). > > No need to repost for this; just let me know what you think and I can > tweak accordingly. What you've written sounds good to me, but I might have just dropped the "behind the same bridge" entirely given your feedback above. Thanks! Logan
