On Mon, 22 Dec 2014, Doug Anderson wrote: > Alan, > > On Mon, Dec 22, 2014 at 8:06 AM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > On Mon, 22 Dec 2014, Wu Liang feng wrote: > > > >> The EHCI controller doesn't properly detect the case when > > > > "The" EHCI controller? I don't know what EHCI controller you're > > talking about, but my controllers don't have any trouble detecting > > device removal during suspend. > > This is specifically the EHCI controller on rk3288. Not sure why Wu > Liang feng removed that part of the description. Maybe it could be put back in. > > Isn't this solution too extreme? What if the device was a flash > > storage drive and it wasn't unplugged during suspend? This patch would > > force it to be removed, messing up any mounted filesystems, when there > > was no need. > > I'm told by Julius (CCed, who knows the USB stack infinitely better > than I do) that you can work around this using "persist". I would > imagine that anyone on a machine using hibernation would run into the > same problem, right? > We asked a lot about this and you can find a whole set of detailed > discussion at: > > https://chromium-review.googlesource.com/#/c/232077/1/drivers/usb/host/ehci-platform.c > > > Since I don't know the USB subsystem particularly well, my review > isn't terribly meaningful, but just in case: > > Reviewed-by: Doug Anderson <dianders@xxxxxxxxxxxx> > > > On rk3288-pinky I have tested that without this patch the EHCI > controller flips out when a USB webcam is plugged into the port and is > power cycled across suspend/resume. With this patch the controller > properly unplugs / replugs the webcam. > > Tested-by: Doug Anderson <dianders@xxxxxxxxxxxx> I assume you also tested the case where the webcam is _not_ power-cycled during the suspend. On Mon, 22 Dec 2014, Julius Werner wrote: > As Doug said, I think persist is the solution. We have essentially the > same case: all we know is that there is now a device connected to the > same port that a device had been connected during suspend... but with > no guarantees whether it is the same device or in the same state. By > forcing people to use persist, we acknowledge that this has the same > risks (e.g. data corruption if a mounted mass storage device was > swapped out for another one), and we benefit from the same safety > checks like comparing the serial number. Okay, I see. This makes sense. Acked-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> 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
