Re: [RFC] xhci: clear port_remote_wakeup on device disconnection

[Mathias Nyman]

On 19.3.2019 16.54, Nicolas Saenz Julienne wrote:
> Hi Oliver, thanks for the review!
>
> On Tue, 2019-03-19 at 12:01 +0100, Oliver Neukum wrote:
> > On Mo, 2019-03-18 at 18:00 +0100, Nicolas Saenz Julienne wrote:
> > > This patch clears "port_remote_wakeup" upon detecting a device
> > > disconnection. Making sure the above mentioned situation doesn't trigger
> > > a PM busyloop.
> >
> > Hi,
> >
> > that is an interesting race condition.

Turns out that port_remote_wakeup was only properly cleared in case of a
successful resume where port stays in U0, or in case of an error where port
goes to inactive state.

In all other cases port_remote_wakeup bit was left uncleared.

> > > Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
> > > ---
> > >   drivers/usb/host/xhci-hub.c | 3 +++
> > >   1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/usb/host/xhci-hub.c b/drivers/usb/host/xhci-hub.c
> > > index e2eece693655..bea853f45aec 100644
> > > --- a/drivers/usb/host/xhci-hub.c
> > > +++ b/drivers/usb/host/xhci-hub.c
> > > @@ -942,6 +942,9 @@ static void xhci_get_usb3_port_status(struct xhci_port
> > > *port, u32 *status,
> > >   			bus_state->suspended_ports &= ~(1 << portnum);
> > >   	}
> > >   
> > > +	if (!(portsc & PORT_CONNECT))
> > > +		bus_state->port_remote_wakeup &= ~(1 << portnum);
> > > +

A check like this should cover the failing resume cases, thanks

We also saw a case when a successful resume was missed as port went into U1
Link power save state (resume->U0->U1) before xhci driver read the port status.

A patch adding U1 and U2 to successful resume states is pending in my for-usb-linus
branch for this.

> > Why are you putting that logic into xhci_get_usb3_port_status()?
> > It looks to me like there is already something related in the caller
>
> You're right, xhci_get_usb3_port_status() is not the ideal spot I'll move the
> code there.

Sounds good, thanks

-Mathias