On Tue, Apr 19, 2022 at 11:28:21AM +0200, Martin Kepplinger wrote: > hi, > > I'm seeing resets and re-enumerations on runtime-resume for one device > a lot. It's a modem connected to the USB2642 Microchip (SMSC) USB2 hub, > that's connected to an xhci HC. > > A remote wakeup *sometimes* makes the hub say "physically disconnected" > during resume in hub_activate(), and thus sets reset_resume. Then the > device comes up as low-speed device once, which again is not allowed > during normal runtime resume, so would itself trigger a reset. Does the reset-resume always fail in this way? > The Hub and device is permanently connected on the PCB, so the hub is > interpreting it in a wrong way. What is the hub is interpreting in a wrong way? Why should a permanent connection on the PCB have anything to do with whether the resume signals are misinterpreted? > I found an email that describes what I > see from Sarah Sharp in 2013 here: > https://marc.info/?l=linux-usb&m=137754385421825&w=2 Where she says: > > "Occasionally, the host controller was sending the SoFs too soon on > resume, and the device would interpret it as a low-speed chirp. The > device would disconnect, and transform from a high speed device to a > low speed device. I don't think increasing the 10 ms time out will > help at all in this case, but you did ask what USB device disconnect > scenarios I've seen." Read the following messages in that email thread. Sarah said that she would fix the SoF signal timing in xhci-hcd ("I agree that this seems like an xHCI driver issue, and I'll fix it in the driver"). I have no idea whether this helped the faulty devices; my guess is that it didn't. (She never did respond to my comment that there is no such thing as a "low-speed chirp".) > I can't find any reference to that bug yet. Has anyone experienced > something (similar) and knows where I can at least try to work around > that? > > I don't know Sarahs' current email, could we forward this question to > her? Sarah hasn't worked on Linux or xhci-hcd for many years. It's probably not worth trying to ask her about this. Alan Stern
