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Date:	Mon, 22 Dec 2014 09:05:38 -0800
From:	Doug Anderson <>
To:	Alan Stern <>
Cc:	Wu Liang feng <>,
	Heiko Stübner <>,
	Tao Huang <>,
	Kever Yang <>,
	Eddie Cai <>,
	Roy Li <>, Chris <>,
	Julius Werner <>,
	Pawel Osciak <>,
	Tomasz Figa <>,
	"" <>,
	"" <>
Subject: Re: [PATCH 2/2] USB: ehci-platform: Support ehci reset after resume quirk


On Mon, Dec 22, 2014 at 8:06 AM, Alan Stern <> 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.

>> a device is removed during suspend. Specifically,when we
>> resume from suspend the EHCI controller maintaining the
>> USB state (FLAG_CF is 1 Current Connect Status is 1) but
>> a USB device (like a USB camera on rk3288) may have been
>> disconnected actually.
>> Let's add a quirk to force ehci to go into the
>> usb_root_hub_lost_power() path and reset after resume.
>> This should generally reset the whole controller and all
>> ports and initialize everything cleanly again, and bring
>> the devices back up.
> 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?

> Can you find a better way to work around the problem?

We asked a lot about this and you can find a whole set of detailed
discussion at:

Since I don't know the USB subsystem particularly well, my review
isn't terribly meaningful, but just in case:

Reviewed-by: Doug Anderson <>

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 <>

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