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

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Date:   Tue, 19 Mar 2019 12:01:28 +0100
From:   Oliver Neukum <oneukum@...e.com>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        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

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);
        }

Otherwise very good catch!

	Regards
		Oliver