linux-kernel - RE: [DISCUSSION] USB device remote wakeup is not working for S3 case

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Date:	Tue, 23 Dec 2014 15:19:47 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Du, Changbin" <changbin.du@...el.com>
cc:	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Wu, Hao" <hao.wu@...el.com>
Subject: RE: [DISCUSSION] USB device remote wakeup is not working for S3 case

On Tue, 23 Dec 2014, Du, Changbin wrote:

> > You have to make sure that wakeup is also enabled for the host
> > controller the device is attached to.  For some host controllers, it
> > may also be necessary to enable wakeup for the root hub.
> > 
> Yes, the root-hub is not wakeup enabled by default, actually hub
> devices are not enabled. It works after I enable it via sysfs interface.

On some hardware, device wakeup requests can work even when root-hub 
wakeup is disabled -- it varies.

In general we do not want hubs to be enabled for wakeup.  If they were, 
then your computer would wake up the moment you unplugged a USB device.  
You would not be able to (for example) to put your laptop to sleep, 
unplug a USB mouse, and put the laptop in its case.

> > > Could we also enable wakeup for usb mouse? Or is there any concern to
> > enable it?
> > > Per my opinion, most people may expect clicking mouse can awake system.
> > 
> > It doesn't matter to me, but you should ask the people on the
> > linux-input mailing list.
> > 
> > Also, what about wakeup for a non-USB mouse?  Shouldn't that be enabled
> > as well?
> Unfortunately the mouse I found are all of usb so cannot confirm it. The
> concern is if we want usb keyboard/mouse wakeup work by default, it does
> make sense only if the parent hubs are also enabled by default.  This is a policy
> issue and may be better place it on userspace. I have no better idea :) .

As mentioned above, it depends on the hardware.

Alan Stern

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