linux-kernel - Re: [PATCH] usb: ehci: s5p: Power-off VBUS during suspend.

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Date:	Tue, 29 Jan 2013 10:21:58 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Vivek Gautam <gautam.vivek@...sung.com>
cc:	linux-usb@...r.kernel.org, <linux-kernel@...r.kernel.org>,
	<linux-samsung-soc@...r.kernel.org>, <gregkh@...uxfoundation.org>,
	<jg1.han@...sung.com>, Doug Anderson <dianders@...omium.org>
Subject: Re: [PATCH] usb: ehci: s5p: Power-off VBUS during suspend.

On Tue, 29 Jan 2013, Vivek Gautam wrote:

> This change de-asserts vbus_gpio on suspend and
> re-asserts on resume in order to save power.
> NOTE, this change means no USB charging in suspend
> mode.

Doing this would mean USB devices could not wake up the system.  This 
would be unacceptable.

However, turning off VBUS power is okay provided:

	no root-hub ports are enabled, and

	the root hub is not enabled for wakeup.

Under those circumstances there can't be any wakeup-enabled USB devices 
on the bus, and the root hub itself would not need to detect new 
connections and disconnections.

Alan Stern

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