linux-kernel - Re: [PATCH] xhci: Disable connect, disconnect and over-current wakeup on system suspend

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Message-ID: <cc190b72-03cc-400b-9dc4-abef21562eff@rowland.harvard.edu>
Date:   Thu, 17 Aug 2023 10:03:18 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Oliver Neukum <oneukum@...e.com>, mathias.nyman@...el.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xhci: Disable connect, disconnect and over-current
 wakeup on system suspend

On Thu, Aug 17, 2023 at 09:13:55PM +0800, Kai-Heng Feng wrote:
> On Thu, Aug 17, 2023 at 8:52 PM Mathias Nyman
> <mathias.nyman@...ux.intel.com> wrote:
> >
> > On 17.8.2023 14.18, Oliver Neukum wrote:
> > > On 17.08.23 11:33, Kai-Heng Feng wrote:
> > >
> > > Hi,
> > >
> > >> So for system-wide suspend, also disable connect, disconnect and
> > >> over-current wakeup to prevent spurious wakeup.
> > >
> > > isn't this breaking the ability to effectively use your root hub
> > > as a source of system wakeups? That is, even if you want the
> > > system to wake up if somebody attaches a new device, it no longer works?
> > >
> >
> > I got the same concern about this.
> 
> Per my test, it doesn't work with or without this change. This applies
> to disconnection too, disconnecting USB devices doesn't wake the
> system up.
> Furthermore, if the newly attached device is a USB keyboard, pressing
> it doesn't wake the system up either. Probably because remote wakeup
> isn't configured when the system is suspended.

If remote wakeup isn't enabled then the do_wakeup variable will be 0, 
so your patch wouldn't make any difference.  The question is what 
happens when remote wakeup _is_ enabled.

Did you check the settings in the controller's and root hub's 
power/wakeup sysfs files?

Alan Stern