lkml.org 
[lkml]   [2014]   [Dec]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/2] USB: ehci-platform: Support ehci reset after resume quirk
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



\
 
 \ /
  Last update: 2014-12-22 22:41    [W:0.067 / U:0.256 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site