On Fri, 7 Feb 2014, Dan Williams wrote: > >> You know, I believe these races would go away if we could delay port > >> pm runtime activation until after the initial discovery of the entire > >> hub topology. One potential way of solving this is to proceed with > >> converting khubd to a workqueue. Then, we could use a properly placed > >> drain_workqueue() to flush the chain of khubd discovery events to > >> completion. > > > > Heh. Strictly speaking, we _never_ discover the entire hub topology. > > A new hub can be plugged in at any time. > > Sometimes I feel like I'm talking to a mathematician ;-) Indeed. > > Of course, we don't care about new hubs being plugged in. It would be > > good enough to wait for only the hubs that were connected when the root > > hubs were registered. I doubt this would be worth the effort, though. > > Right, once one drain_workqueue() event has completed we assume that > everything plugged in at hcd registration has had a chance to be > discovered. At least this is the same guarantee that libsas makes, it > has a similar problem determining when it has completed initial domain > discovery / expander enumeration. For tier-mismatch we only care > about internal hubs, barring some internal switching those should > always be part of the initial scan. Assuming the manufacturers follow the spec (tier mismatch is limited to a single integrated hub on each non-SuperSpeed external port), it should work. > I don't think it's too much to add. I'll take a stab at it (after we > settle on this current set) and if you think it's too onerous feel > free to nak it. Fair enough. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
