Messages in this thread | | | Date | Mon, 22 Dec 2014 16:04:53 -0500 (EST) | From | Alan Stern <> | Subject | Re: [PATCH 2/2] USB: ehci-platform: Support ehci reset after resume quirk |
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On Mon, 22 Dec 2014, Doug Anderson wrote:
> Alan, > > On Mon, Dec 22, 2014 at 8:06 AM, Alan Stern <stern@rowland.harvard.edu> 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@chromium.org> > > > 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@chromium.org>
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@rowland.harvard.edu>
Alan Stern
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