netdev - Re: [PATCH 1/2] smsc75xx: refactor entering suspend modes

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Date:	Tue, 27 Nov 2012 14:46:38 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Bjørn Mork <bjorn@...k.no>
cc:	Steve Glendinning <steve@...well.net>,
	netdev <netdev@...r.kernel.org>, <linux-usb@...r.kernel.org>
Subject: Re: [PATCH 1/2] smsc75xx: refactor entering suspend modes

On Tue, 27 Nov 2012, Bjørn Mork wrote:

> Steve Glendinning <steve@...well.net> writes:
> 
> > Hi Bjorn,
> >
> > On 27 November 2012 17:21, Steve Glendinning <steve@...well.net> wrote:
> >> Hi Bjorn,
> >>
> >>>> +     smsc75xx_set_feature(dev, USB_DEVICE_REMOTE_WAKEUP);
> >>>
> >>> As mentioned in another comment to the smsc95xx driver: This is weird.
> >>> Do you really need to do that?
> >>>
> >>> This is an USB interface driver.  The USB device is handled by the
> >>> generic "usb" driver, which will do the right thing.  See
> >>> drivers/usb/generic.c and drivers/usb/core/hub.c
> >>
> >> Thanks, I've tested removing all these calls from the driver and
> >> wakeup functionality seems to still work.
> >>
> >> I'll resubmit my smsc75xx enhancement patchset with this change once
> >> I've done some more testing.
> >
> > Further testing shows that removing these calls stop wakeup from
> > system suspend working (although don't appear to impact runtime
> > autosuspend).  Have I missed a flag or somewhere that causes
> > udev->do_remote_wakeup to be set in the code you posted?
> 
> udev->do_remote_wakeup is set in choose_wakeup() in
> drivers/usb/core/driver.c.  AFAICS it is always set as long as
> device_may_wakeup(&udev->dev) is true.

That's right.  But is device_may_wakeup(&udev->dev) true?

By default it wouldn't be.  The normal way to set it is for the user or 
a program to do:

	echo enabled >/sys/bus/usb/devices/.../power/wakeup

Of course, a driver could disregard the user's choice and set the flag 
by itself.

Alan Stern

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