Messages in this thread | | | From | Logan Gunthorpe <> | Date | Thu, 10 Jun 2021 16:25:53 -0600 | Subject | Re: [PATCH v1 1/6] PCI/P2PDMA: Rename upstream_bridge_distance() and rework documentation |
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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
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