linux-kernel - Re: [RFC] xhci: clear port_remote

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Date:   Tue, 19 Mar 2019 15:54:21 +0100
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     Oliver Neukum <oneukum@...e.com>,
        Mathias Nyman <mathias.nyman@...el.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [RFC] xhci: clear port_remote_wakeup on device disconnection

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.
> 
> > Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
> > ---
> >  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);
> > +
> >  	xhci_hub_report_usb3_link_state(xhci, status, portsc);
> >  	xhci_del_comp_mod_timer(xhci, portsc, portnum);
> >  }
> 
> 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
> 
>         /* USB2 and USB3 specific bits, including Port Link State */
>         if (hcd->speed >= HCD_USB3)
>                 xhci_get_usb3_port_status(port, &status, raw_port_status);
>         else
>                 xhci_get_usb2_port_status(port, &status, raw_port_status,
>                                           flags);
>         /*
>          * Clear stale usb2 resume signalling variables in case port changed
>          * state during resume signalling. For example on error
>          */
>         if ((bus_state->resume_done[wIndex] ||
>              test_bit(wIndex, &bus_state->resuming_ports)) &&
>             (raw_port_status & PORT_PLS_MASK) != XDEV_U3 &&
>             (raw_port_status & PORT_PLS_MASK) != XDEV_RESUME) {
>                 bus_state->resume_done[wIndex] = 0;
>                 clear_bit(wIndex, &bus_state->resuming_ports);
>                 usb_hcd_end_port_resume(&hcd->self, wIndex);
>         }

You're right, xhci_get_usb3_port_status() is not the ideal spot I'll move the
code there.

> 
> Otherwise very good catch!
> 
> 	Regards
> 		Oliver
> 


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