linux-kernel - Re: [PATCH] usb: core: Avoid doing warm reset on disconnect event

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Date:   Fri, 26 Nov 2021 19:49:27 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     stern@...land.harvard.edu, mathias.nyman@...ux.intel.com,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Bixuan Cui <cuibixuan@...wei.com>,
        Andrew Lunn <andrew@...n.ch>,
        Chris Chiu <chris.chiu@...onical.com>,
        Rajat Jain <rajatja@...gle.com>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: core: Avoid doing warm reset on disconnect event

On Fri, Nov 26, 2021 at 2:53 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Fri, Nov 26, 2021 at 11:26:21AM +0800, Kai-Heng Feng wrote:
> > Unplugging USB device may cause an incorrect warm reset loop:
> > [  143.039019] xhci_hcd 0000:00:14.0: Port change event, 2-3, id 19, portsc: 0x4202c0
> > [  143.039025] xhci_hcd 0000:00:14.0: handle_port_status: starting usb2 port polling.
> > [  143.039051] hub 2-0:1.0: state 7 ports 10 chg 0000 evt 0008
> > [  143.039058] xhci_hcd 0000:00:14.0: Get port status 2-3 read: 0x4202c0, return 0x4102c0
> > [  143.039092] xhci_hcd 0000:00:14.0: clear port3 connect change, portsc: 0x4002c0
> > [  143.039096] usb usb2-port3: link state change
> > [  143.039099] xhci_hcd 0000:00:14.0: clear port3 link state change, portsc: 0x2c0
> > [  143.039101] usb usb2-port3: do warm reset
> > [  143.096736] xhci_hcd 0000:00:14.0: Get port status 2-3 read: 0x2b0, return 0x2b0
> > [  143.096751] usb usb2-port3: not warm reset yet, waiting 50ms
> > [  143.131500] xhci_hcd 0000:00:14.0: Can't queue urb, port error, link inactive
> > [  143.138260] xhci_hcd 0000:00:14.0: Port change event, 2-3, id 19, portsc: 0x2802a0
> > [  143.138263] xhci_hcd 0000:00:14.0: handle_port_status: starting usb2 port polling.
> > [  143.160756] xhci_hcd 0000:00:14.0: Get port status 2-3 read: 0x2802a0, return 0x3002a0
> > [  143.160798] usb usb2-port3: not warm reset yet, waiting 200ms
> >
> > The warm reset is due to its PLS is in eSS.Inactive state. However, USB
> > 3.2 spec table 10-13 mentions "Ports can be disabled by either a fault
> > condition (disconnect event or other fault condition)", xHCI 1.2 spec
> > table 5-27 also states that "This flag shall automatically be cleared to
> > ‘0’ by a disconnect event or other fault condition." on PED.
> >
> > So use CSC = 0 and PED = 0 as indication that device is disconnecting to
> > avoid doing warm reset.
> >
> > Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> > ---
> >  drivers/usb/core/hub.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> > index 86658a81d2844..abd5a83d194b0 100644
> > --- a/drivers/usb/core/hub.c
> > +++ b/drivers/usb/core/hub.c
> > @@ -5530,6 +5530,7 @@ static void port_event(struct usb_hub *hub, int port1)
> >               __must_hold(&port_dev->status_lock)
> >  {
> >       int connect_change;
> > +     int disconnect = 0;
>
> bool?

Will change.

>
> >       struct usb_port *port_dev = hub->ports[port1 - 1];
> >       struct usb_device *udev = port_dev->child;
> >       struct usb_device *hdev = hub->hdev;
> > @@ -5545,6 +5546,9 @@ static void port_event(struct usb_hub *hub, int port1)
> >       if (portchange & USB_PORT_STAT_C_CONNECTION) {
> >               usb_clear_port_feature(hdev, port1, USB_PORT_FEAT_C_CONNECTION);
> >               connect_change = 1;
> > +             if (!(portstatus & USB_PORT_STAT_CONNECTION) &&
> > +                 !(portstatus & USB_PORT_STAT_ENABLE))
> > +                     disconnect = 1;
> >       }
> >
> >       if (portchange & USB_PORT_STAT_C_ENABLE) {
> > @@ -5613,7 +5617,7 @@ static void port_event(struct usb_hub *hub, int port1)
> >        * Warm reset a USB3 protocol port if it's in
> >        * SS.Inactive state.
> >        */
> > -     if (hub_port_warm_reset_required(hub, port1, portstatus)) {
> > +     if (hub_port_warm_reset_required(hub, port1, portstatus) && !disconnect) {
>
> Why is this problem just showing up now?  What commit caused this
> regression?

It's not a regression, the issue happens on all kernels I tried.
port_event() stays unchanged for a while.

Kai-Heng

>
> thanks,
>
> greg k-h