linux-kernel - Re: [PATCH 2/2] USB: ehci-platform: Support ehci reset after resume quirk

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Date:	Mon, 22 Dec 2014 11:06:20 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Wu Liang feng <wulf@...k-chips.com>
cc:	heiko@...ech.de, <huangtao@...k-chips.com>,
	<kever.yang@...k-chips.com>, <eddie.cai@...k-chips.com>,
	<roy.li@...k-chips.com>, <zyw@...k-chips.com>,
	<jwerner@...gle.com>, <dianders@...gle.com>, <posciak@...gle.com>,
	<tfiga@...gle.com>, <linux-kernel@...r.kernel.org>,
	<linux-usb@...r.kernel.org>
Subject: Re: [PATCH 2/2] USB: ehci-platform: Support ehci reset after resume
 quirk

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.

> 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.

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

Alan Stern

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