linux-kernel - Re: [PATCH v2] usb: core: Avoid doing warm reset on disconnect event

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Date:   Tue, 30 Nov 2021 10:36:13 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc:     gregkh@...uxfoundation.org, stern@...land.harvard.edu,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Andrew Lunn <andrew@...n.ch>, Rajat Jain <rajatja@...gle.com>,
        Chris Chiu <chris.chiu@...onical.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] usb: core: Avoid doing warm reset on disconnect event

On Mon, Nov 29, 2021 at 6:18 PM Mathias Nyman
<mathias.nyman@...ux.intel.com> wrote:
>
> On 26.11.2021 13.56, 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.
>
> My understanding is that PED = 0 in case of disconnect, error (PLS=Inactive), or
> during active reset signalling. See xHCI Figure 4-27: USB3 Root Hub Port State Machine.
> signal states (0,0,0,0) are PP,CCS,PED,PR.

I think it's 1,0,0,0? So for my case, the port is in Error state (PLS
= Inactive, 1,0,0,0).

>
> I'm looking at a similar case where Inactive link is reported at disconnect for a while
> before missing terminations are detected and link finally goes to RxDetect.

So the PLS goes from Inactive to RxDetect after a while?
Is the case you are working on also EHL?

>
> If the port was reset immediately when Inactive link state was reported the port stays stuck
> in port reset.
> This might have been related to the address0 locking issues recently fixed.
>
> Anyway, to avoid the extra reset of a removed USB3 device I started polling the link state of
> the Inactive link for some time before resetting it. This gives the link time to detect
> missing terminations and go to RxDetect, and driver can skip the reset.
>
> Planning on upstreaming it, patch is here:
> https://git.kernel.org/pub/scm/linux/kernel/git/mnyman/xhci.git/commit/?h=fix_avoid_disconnect_reset&id=72d20c026b7812d096c6b5184a3888894401c829

Thanks, let me test this out.

Kai-Heng

>
> -Mathias