On Thu, 6 Feb 2014, Alan Stern wrote:
> On Fri, 31 Jan 2014, Dan Williams wrote:
>
> > If a port is powered-off, or in the process of being powered-off, prevent
> > khubd from operating on it. Otherwise, the following sequence of events
> > leading to an unintended disconnect may occur:
> >
> > Events:
> > (0) <set pm_qos_no_poweroff to '0' for port1>
> > (1) hub 2-2:1.0: hub_resume
> > (2) hub 2-2:1.0: port 1: status 0301 change 0000
> > (3) hub 2-2:1.0: state 7 ports 4 chg 0002 evt 0000
> > (4) hub 2-2:1.0: port 1, power off status 0000, change 0000, 12 Mb/s
> > (5) usb 2-2.1: USB disconnect, device number 5
> >
> > Description:
> > (1) hub is resumed before sending a ClearPortFeature request
> > (2) hub_activate() notices the port is connected and sets
> > hub->change_bits for the port
> > (3) hub_events() starts, but at the same time the port suspends
> > (4) hub_connect_change() sees the disabled port and triggers disconnect
>
> > --- a/drivers/usb/core/hub.c
> > +++ b/drivers/usb/core/hub.c
> > @@ -4728,32 +4728,41 @@ static void port_event(struct usb_hub *hub, int port1)
> > USB_PORT_FEAT_C_PORT_CONFIG_ERROR);
> > }
> >
> > - if (hub_handle_remote_wakeup(hub, port1, portstatus, portchange))
> > - connect_change = 1;
> > -
> > - /* Warm reset a USB3 protocol port if it's in
> > - * SS.Inactive state.
> > - */
> > - if (hub_port_warm_reset_required(hub, portstatus)) {
> > - int status;
> > + /* take port actions that require the port to be powered on */
> > + pm_runtime_get_noresume(&port_dev->dev);
> > + pm_runtime_barrier(&port_dev->dev);
> > + if (pm_runtime_active(&port_dev->dev)) {
> > + if (hub_handle_remote_wakeup(hub, port1,
> > + portstatus, portchange))
> > + connect_change = 1;
>
> When there is a remote wakeup request pending, we want to handle it
> even if the port is powered off.
On second thought, this can't happen since we never power-down a port
if the child device is enabled for remote wakeup. Never mind...
Alan Stern
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