linux-kernel - Re: [PATCH v2] usb: hub: Add delay for SuperSpeed hub resume to let links transit to U0

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Message-ID: <CAAd53p5thAHXdmmEn9VV7nrWGu7W6UaEsB7hx7k9WYTBMG2GqQ@mail.gmail.com>
Date:   Thu, 16 Dec 2021 08:23:29 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     gregkh@...uxfoundation.org, mathias.nyman@...ux.intel.com,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Chris Chiu <chris.chiu@...onical.com>,
        Bixuan Cui <cuibixuan@...wei.com>,
        Rajat Jain <rajatja@...gle.com>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] usb: hub: Add delay for SuperSpeed hub resume to let
 links transit to U0

On Wed, Dec 15, 2021 at 11:47 PM Alan Stern <stern@...land.harvard.edu> wrote:
>
> On Wed, Dec 15, 2021 at 08:01:06PM +0800, Kai-Heng Feng wrote:
> > When a new USB device gets plugged to nested hubs, the affected hub,
> > which connects to usb 2-1.4-port2, doesn't report there's any change,
> > hence the nested hubs go back to runtime suspend like nothing happened:
> > [  281.032951] usb usb2: usb wakeup-resume
> > [  281.032959] usb usb2: usb auto-resume
> > [  281.032974] hub 2-0:1.0: hub_resume
> > [  281.033011] usb usb2-port1: status 0263 change 0000
> > [  281.033077] hub 2-0:1.0: state 7 ports 4 chg 0000 evt 0000
> > [  281.049797] usb 2-1: usb wakeup-resume
> > [  281.069800] usb 2-1: Waited 0ms for CONNECT
> > [  281.069810] usb 2-1: finish resume
> > [  281.070026] hub 2-1:1.0: hub_resume
> > [  281.070250] usb 2-1-port4: status 0203 change 0000
> > [  281.070272] usb usb2-port1: resume, status 0
> > [  281.070282] hub 2-1:1.0: state 7 ports 4 chg 0010 evt 0000
> > [  281.089813] usb 2-1.4: usb wakeup-resume
> > [  281.109792] usb 2-1.4: Waited 0ms for CONNECT
> > [  281.109801] usb 2-1.4: finish resume
> > [  281.109991] hub 2-1.4:1.0: hub_resume
> > [  281.110147] usb 2-1.4-port2: status 0263 change 0000
> > [  281.110234] usb 2-1-port4: resume, status 0
> > [  281.110239] usb 2-1-port4: status 0203, change 0000, 10.0 Gb/s
> > [  281.110266] hub 2-1.4:1.0: state 7 ports 4 chg 0000 evt 0000
> > [  281.110426] hub 2-1.4:1.0: hub_suspend
> > [  281.110565] usb 2-1.4: usb auto-suspend, wakeup 1
> > [  281.130998] hub 2-1:1.0: hub_suspend
> > [  281.137788] usb 2-1: usb auto-suspend, wakeup 1
> > [  281.142935] hub 2-0:1.0: state 7 ports 4 chg 0000 evt 0000
> > [  281.177828] usb 2-1: usb wakeup-resume
> > [  281.197839] usb 2-1: Waited 0ms for CONNECT
> > [  281.197850] usb 2-1: finish resume
> > [  281.197984] hub 2-1:1.0: hub_resume
> > [  281.198203] usb 2-1-port4: status 0203 change 0000
> > [  281.198228] usb usb2-port1: resume, status 0
> > [  281.198237] hub 2-1:1.0: state 7 ports 4 chg 0010 evt 0000
> > [  281.217835] usb 2-1.4: usb wakeup-resume
> > [  281.237834] usb 2-1.4: Waited 0ms for CONNECT
> > [  281.237845] usb 2-1.4: finish resume
> > [  281.237990] hub 2-1.4:1.0: hub_resume
> > [  281.238067] usb 2-1.4-port2: status 0263 change 0000
> > [  281.238148] usb 2-1-port4: resume, status 0
> > [  281.238152] usb 2-1-port4: status 0203, change 0000, 10.0 Gb/s
> > [  281.238166] hub 2-1.4:1.0: state 7 ports 4 chg 0000 evt 0000
> > [  281.238385] hub 2-1.4:1.0: hub_suspend
> > [  281.238523] usb 2-1.4: usb auto-suspend, wakeup 1
> > [  281.258076] hub 2-1:1.0: hub_suspend
> > [  281.265744] usb 2-1: usb auto-suspend, wakeup 1
> > [  281.285976] hub 2-0:1.0: hub_suspend
> > [  281.285988] usb usb2: bus auto-suspend, wakeup 1
> >
> > USB 3.2 spec, 9.2.5.4 "Changing Function Suspend State" says that "If
> > the link is in a non-U0 state, then the device must transition the link
> > to U0 prior to sending the remote wake message", but the hub only
> > transits the link to U0 after signaling remote wakeup.
> >
> > So be more forgiving and use a 20ms delay to let the link transit to U0
> > for remote wakeup.
> >
> > Suggested-by: Alan Stern <stern@...land.harvard.edu>
> > Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> > ---
> > v2:
> >  - Add a small delay instead of waking up all hubs.
> >
> >  drivers/usb/core/hub.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> > index 00070a8a65079..576fdf2c9f3c8 100644
> > --- a/drivers/usb/core/hub.c
> > +++ b/drivers/usb/core/hub.c
> > @@ -1110,7 +1110,10 @@ static void hub_activate(struct usb_hub *hub, enum hub_activation_type type)
> >               } else {
> >                       hub_power_on(hub, true);
> >               }
> > -     }
> > +     /* Give some time on remote wakeup to let links to transit to U0 */
> > +     } else if (hub_is_superspeed(hub->hdev))
> > +             msleep(20);
>
> Where did the 20-ms number come from?  Is it mentioned in the spec as
> the time required for a port to switch from U3 to U0?

The 20ms is the minimal time the device take to bring link back to U0 reliably.
The spec mentioned device has to transit the link to U0 before
signaling remote wakeup.
So do you think this requires a new quirk?

Kai-Heng

>
> Alan Stern