On Fri, Dec 13, 2013 at 9:48 AM, Sarah Sharp <sarah.a.sharp@xxxxxxxxxxxxxxx> wrote: > On Thu, Dec 12, 2013 at 11:05:04AM -0500, Alan Stern wrote: >> On Wed, 11 Dec 2013, Julius Werner wrote: >> >> > >> ...although, the spec says that it does not wait for the port resets >> > >> to complete. As far as I can see re-issuing a warm reset and waiting >> > >> is the only way to guarantee the core times the recovery. Presumably >> > >> the portstatus debounce in hub_activate() mitigates this, but that >> > >> 100ms is less than a full reset timeout. >> > >> > It's definitely not just a timing issue for us. I can't reproduce all >> > the same cases as Vikas, but when I attach a USB analyzer to the ones >> > I do see the host controller doesn't even start sending a reset. >> > >> > >>> The xHCI spec requires that when the xHCI host is reset, a USB reset is >> > >>> driven down the USB 3.0 ports. If hot reset fails, the port may migrate >> > >>> to warm reset. See table 32 in the xHCI spec, in the definition of >> > >>> HCRST. It sounds like this host doesn't drive a USB reset down USB 3.0 >> > >>> ports at all on host controller reset? >> > >> > Oh, interesting, I hadn't seen that yet. So I guess the spec itself is >> > fine if it were followed to the letter. >> > >> > I did some more tests about this on my Exynos machine: when I put a >> > device to autosuspend (U3) and manually poke the xHC reset bit, I do >> > see an automatic warm reset on the analyzer and the ports manage to >> > retrain to U0. But after a system suspend/resume which calls >> > xhci_reset() in the process, there is no reset on the wire. I also >> > noticed that it doesn't drive a reset (even after manual poking) when >> > there is no device connected on the other end of the analyzer. >> > >> > So this might be our problem: maybe these host controllers (Synopsys >> > DesignWare) issue the spec-mandated warm reset only on ports where >> > they think there is a device attached. But after a system >> > suspend/resume (where the whole IP block on the SoC was powered down), >> > the host controller cannot know that there is still a device with an >> > active power session attached, and therefore doesn't drive the reset >> > on its own. > > Ok, that makes some sense. I could see why host controllers wouldn't > want to drive reset on an unconnected port. > >> > Even though this is a host controller bug, we still have to deal with >> > it somehow. I guess we could move the code into xhci_plat_resume() and >> > hide it behind a quirk to lessen the impact. But since reset_resume is >> > not a common case for most host controllers, it's hard to say if this >> > is DesignWare specific or a more widespread implementation mistake. >> >> I was going to suggest something along these lines too. This seems to >> be a bug in xHCI. Therefore the fix belongs in xhci-hcd, not in the >> hub driver. > > I agree. Is there a chance that the Synopsys DesignWare will be a PCI > device instead of a platform device? If so, it would be better to put > the code into xhci_resume instead of xhci_plat_resume. That also allows > you to only issue the warm reset when the register restore state command > fails, after the xhci_reset call. > > Also, I assume that other systems with the Synopsys DesignWare IP will > experience this issue? I know of at least two other chipsets that will > include that IP, and it would be good to find a way to trigger on the > Synopsys IP, rather than off xHCI PCI vendor and device ID. Otherwise > we'll be adding PCI IDs to the xHCI driver quirks for many many kernels > to come. > > I'm actually leaning towards enabling the check for warm reset broadly. > It seems like it wouldn't hurt to issue a warm reset on the USB 3.0 > ports if they're in compliance, poll, or rx.detect. So, let's enable > this broadly in xhci_resume, mark the patch for stable, but ask for the > backport to be delayed until 3.13.3 is out, to allow for more testing. > If anyone complains of xHCI behavior changes, we'll change the code to > add a quirk. Is there a clean way to make this per-port rather than globally at xhci_resume()? I am looking to hook into this for port power recovery as Tianyu's testing encountered "warm reset required" conditions at runtime_resume. I'm still on the hunt for a solid reproducer, but it indicates this is a more general quirk with power session recovery. -- 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
