linux-kernel - Re: [REPOST PATCH 3/3] USB: dwc2: Don't turn off the usbphy in suspend if wakeup is enabled

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Date:	Tue, 7 Jul 2015 10:28:34 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Felipe Balbi <balbi@...com>
cc:	Douglas Anderson <dianders@...omium.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	John Youn <johnyoun@...opsys.com>, <linux-usb@...r.kernel.org>,
	Chris Zhong <zyw@...k-chips.com>,
	Heiko Stuebner <heiko@...ech.de>,
	Julius Werner <jwerner@...omium.org>,
	Andrew Bresticker <abrestic@...omium.org>,
	Alexandru Stan <amstan@...omium.org>, <lyz@...k-chips.com>,
	<linux-rockchip@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [REPOST PATCH 3/3] USB: dwc2: Don't turn off the usbphy in
 suspend if wakeup is enabled

On Mon, 6 Jul 2015, Felipe Balbi wrote:

> > You know, this is the first time I've run across this optimization.
> > 
> > In principle it applies to any USB host controller, not just to PHYs.  
> > There's no reason to enable wakeup for a controller if none of the 
> > attached devices can issue a wakeup request.
> > 
> > I don't know if implementing this in other HCDs would save any power.  
> > Any ideas?
> 
> most likely it would. Enabling wakeup usually boils down to keeping a
> tiny part of the controller (or PHY) powered up. Sometimes that lies in
> an always-on power domain, so there would be no difference.

Doug, how would you feel about reworking the patch that exports
usb_wakeup_enabled_descendants()?  Instead of doing it that way, create
and export a new subroutine in hcd.c called
usb_hcd_wakeup_not_needed(), or something similar.

The idea is that a host controller driver can do something like this:

	do_wakeup = device_may_wakeup(...);
	if (usb_hcd_wakeup_not_needed(hcd))
		do_wakeup = false;

It encapsulates what you want in a form that can easily be used by 
every HCD.  We can then add this call into the HCDs, over time.

(Merging a change like this would be a challenge.  I guess Felipe would
have to put it in a separate branch which Greg could pull, or vice
versa, so that the new routine would be available to patches submitted
to either maintainer.)

Alan Stern

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