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

[Kai-Heng Feng]

On Fri, Dec 3, 2021 at 10:16 PM Mathias Nyman
<mathias.nyman@xxxxxxxxxxxxxxx> wrote:
>
> On 2.12.2021 5.10, Kai-Heng Feng wrote:
> > On Tue, Nov 30, 2021 at 10:36 AM Kai-Heng Feng
> > <kai.heng.feng@xxxxxxxxxxxxx> wrote:
> >>
> >> On Mon, Nov 29, 2021 at 6:18 PM Mathias Nyman
> >> <mathias.nyman@xxxxxxxxxxxxxxx> 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).
>
> Yes, Port power is still on, so (1,0,0,0) but PED and CCS are both 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?
>
> Not EHL this time, anoter platform.
>
> >>
> >>>
> >>> 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.
> >
> > The result is negative, here's the relevant log:
> > [  128.219129] xhci_hcd 0000:00:14.0: Port change event, 2-2, id 18,
> > portsc: 0x4202c0
> > [  128.219143] xhci_hcd 0000:00:14.0: handle_port_status: starting port polling.
> > [  128.219201] hub 2-0:1.0: state 7 ports 10 chg 0000 evt 0004
> > [  128.219217] xhci_hcd 0000:00:14.0: Get port status 2-2 read:
> > 0x4202c0, return 0x4102c0
> > [  128.219244] xhci_hcd 0000:00:14.0: clear port2 connect change,
> > portsc: 0x4002c0
> > [  128.219256] usb usb2-port2: link state change
> > [  128.219264] xhci_hcd 0000:00:14.0: clear port2 link state change,
> > portsc: 0x2c0
> > [  128.232326] xhci_hcd 0000:00:14.0: xhci_hub_status_data: stopping
> > port polling.
> > [  128.244356] xhci_hcd 0000:00:14.0: Get port status 2-2 read: 0x2c0,
> > return 0x2c0
> > [  128.244383] usb usb2-port2: Wait for inactive link disconnect detect
> > [  128.272342] xhci_hcd 0000:00:14.0: Get port status 2-2 read: 0x2c0,
> > return 0x2c0
> > [  128.272370] usb usb2-port2: Wait for inactive link disconnect detect
> > [  128.300348] xhci_hcd 0000:00:14.0: Get port status 2-2 read: 0x2c0,
> > return 0x2c0
> > [  128.300375] usb usb2-port2: Wait for inactive link disconnect detect
> > [  128.328342] xhci_hcd 0000:00:14.0: Get port status 2-2 read: 0x2c0,
> > return 0x2c0
> > [  128.328369] usb usb2-port2: Wait for inactive link disconnect detect
> > [  128.356343] xhci_hcd 0000:00:14.0: Get port status 2-2 read: 0x2c0,
> > return 0x2c0
> > [  128.356370] usb usb2-port2: Wait for inactive link disconnect detect
> > [  128.356374] usb usb2-port2: do warm reset, port only
> > [  128.377500] xhci_hcd 0000:00:14.0: Port change event, 1-2, id 2,
> > portsc: 0x206e1
> > [  128.377515] xhci_hcd 0000:00:14.0: handle_port_status: starting port polling.
> > [  128.377570] hub 1-0:1.0: state 7 ports 16 chg 0000 evt 0004
> > [  128.377586] xhci_hcd 0000:00:14.0: Get port status 1-2 read:
> > 0x206e1, return 0x10101
> > [  128.377614] xhci_hcd 0000:00:14.0: clear port2 connect change, portsc: 0x6e1
> > [  128.377626] usb usb1-port2: status 0101, change 0001, 12 Mb/s
> > [  128.377636] xhci_hcd 0000:00:14.0: Get port status 1-2 read: 0x6e1,
> > return 0x101
> > [  128.398304] xhci_hcd 0000:00:14.0: Port change event, 1-2, id 2,
> > portsc: 0x202a0
> > [  128.398319] xhci_hcd 0000:00:14.0: handle_port_status: starting port polling.
> > [  128.412343] xhci_hcd 0000:00:14.0: Get port status 1-2 read:
> > 0x202a0, return 0x10100
> > [  128.412376] xhci_hcd 0000:00:14.0: clear port2 connect change, portsc: 0x2a0
> > [  128.416337] xhci_hcd 0000:00:14.0: Get port status 2-2 read: 0x2b0,
> > return 0x2b0
> > [  128.416368] usb usb2-port2: not warm reset yet, waiting 50ms
> > [  128.448341] xhci_hcd 0000:00:14.0: Get port status 1-2 read: 0x2a0,
> > return 0x100
> > [  128.476335] xhci_hcd 0000:00:14.0: Get port status 2-2 read: 0x2f0,
> > return 0x2f0
> > [  128.476366] usb usb2-port2: not warm reset yet, waiting 200ms
> > [  128.480332] xhci_hcd 0000:00:14.0: xhci_hub_status_data: stopping
> > port polling.
> > [  128.484343] xhci_hcd 0000:00:14.0: Get port status 1-2 read: 0x2a0,
> > return 0x100
> > [  128.520323] xhci_hcd 0000:00:14.0: Get port status 1-2 read: 0x2a0,
> > return 0x100
> > [  128.556325] xhci_hcd 0000:00:14.0: Get port status 1-2 read: 0x2a0,
> > return 0x100
> > [  128.556353] usb usb1-port2: debounce total 125ms stable 100ms status 0x100
> > [  128.556366] hub 1-0:1.0: state 7 ports 16 chg 0000 evt 0004
> > [  128.556376] xhci_hcd 0000:00:14.0: Get port status 1-2 read: 0x2a0,
> > return 0x100
> > [  128.684329] xhci_hcd 0000:00:14.0: Get port status 2-2 read: 0x2f0,
> > return 0x2f0
> > [  128.684360] usb usb2-port2: not warm reset yet, waiting 200ms
> > [  128.892325] xhci_hcd 0000:00:14.0: Get port status 2-2 read: 0x2f0,
> > return 0x2f0
> > [  128.892357] usb usb2-port2: not warm reset yet, waiting 200ms
> > [  129.100317] xhci_hcd 0000:00:14.0: Get port status 2-2 read: 0x2f0,
> > return 0x2f0
> > [  129.100348] usb usb2-port2: not warm reset yet, waiting 200ms
> > [  129.100354] hub 2-0:1.0: port_wait_reset: err = -16
> > [  129.100358] usb usb2-port2: not enabled, trying warm reset again...
> >
>
> Ok, so after port 2-2 was stuck in inactive (2c0) for long enough we reset it.
> It goes to RxDetect with reset asserted(2b0), and then to polling with reset asserted(2f0).
> The "RxDetect" and "polling" link states are not very reliable while reset is asserted.
>
> So problem 1 is that port stays in Inactive for a long time even if device was disconnected.
> Issue 2 is that reset never completes. We are stuck in reset.
>
> Just out of curiosity, does the link go to "RxDetect" from "inactive" if we just
> increase the retry, or is it really stuck in inactive state?

The result is still negative.

Kai-Heng

>
> i.e.
> -#define DETECT_DISCONNECT_TRIES 5
> +#define DETECT_DISCONNECT_TRIES 20
>
> -Mathias