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    SubjectRe: [PATCH v2] usb: core: Avoid doing warm reset on disconnect event
    On Mon, Nov 29, 2021 at 6:18 PM Mathias Nyman
    <mathias.nyman@linux.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

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