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 <20210510145030.1495-2-chris.chiu@canonical.com> <20210510150203.GD863718@rowland.harvard.edu>
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From:   Chris Chiu <chris.chiu@canonical.com>
Date:   Tue, 11 May 2021 13:04:36 +0800
Message-ID: <CABTNMG24BOS_+uGEYFLJrmEW10eTGjrOowwS7Zb_U+AvkZWTyQ@mail.gmail.com>
Subject: Re: [PATCH v2 1/2] USB: reset-resume the device when PORT_SUSPEND is
 set but timeout
To:     Alan Stern <stern@rowland.harvard.edu>
Cc:     Greg KH <gregkh@linuxfoundation.org>, m.v.b@runbox.com,
        hadess@hadess.net, linux-usb@vger.kernel.org,
        Linux Kernel <linux-kernel@vger.kernel.org>
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On Mon, May 10, 2021 at 11:02 PM Alan Stern <stern@rowland.harvard.edu> wrote:
>
> On Mon, May 10, 2021 at 10:50:29PM +0800, chris.chiu@canonical.com wrote:
> > From: Chris Chiu <chris.chiu@canonical.com>
> >
> > On the Realtek high-speed Hub(0bda:5487), the port which has wakeup
> > enabled_descendants will sometimes timeout when setting PORT_SUSPEND
> > feature. After checking the PORT_SUSPEND bit in wPortStatus, it is
> > already set. However, the hub will fail to activate because the
> > PORT_SUSPEND feature of that port is not cleared during resume. All
> > connected devices are lost after resume.
> >
> > This commit force reset-resume the device connected to the timeout
> > but suspended port so that the hub will have chance to clear the
> > PORT_SUSPEND feature during resume.
>
> Are you certain that the reset-resume is needed?  What happens if you
> leave out the line that sets udev->reset_resume?  The rest of the patch
> will cause the kernel to realize that the port really is suspended, so
> maybe the suspend feature will get cleared properly during resume.
>
> It's worthwhile to try the experiement and see what happens.
>
> Alan Stern
>

If I leave out the udev->reset_resume set, the resume will fail. Please refer
to the following kernel log. The usb 1-1 is the hub which has wakeup enabled
descendants.

[   57.210472] usb 1-1: kworker/u32:7 timed out on ep0out len=0/0
[   57.211022] usb 1-1-port3: suspend timeout, status 0507
[   57.211130] hub 1-1:1.0: hub_suspend
[   57.230500] usb 1-1: usb suspend, wakeup 0

The timeout happens at 57.210472 and you can see the PORT_SUSPEND
bit is actually set in the "status 0507". The following shows the resume log.

[   58.046556] usb 1-1: usb resume
[   58.114515] usb 1-1: Waited 0ms for CONNECT
[   58.114524] usb 1-1: finish resume
[   58.114928] hub 1-1:1.0: hub_resume
[   58.116035] usb 1-1-port3: status 0507 change 0000
[   58.116720] usb 1-1-port5: status 0503 change 0000
[   58.116778] hub 1-1.3:1.0: hub_resume
[   58.116908] hub 1-1.3:1.0: hub_ext_port_status failed (err = -71)
[   58.116952] usb 1-1.5: Waited 0ms for CONNECT
[   58.116955] usb 1-1.5: finish resume
[   58.117157] hub 1-1.3:1.0: hub_ext_port_status failed (err = -71)
[   58.117397] usb 1-1.3-port5: can't resume, status -71
[   58.117782] hub 1-1.3:1.0: hub_ext_port_status failed (err = -71)
[   58.118147] usb 1-1.3-port2: can't resume, status -71
[   58.118149] usb 1-1.3.2: Waited 0ms for CONNECT
[   58.118151] usb 1-1.3-port2: status 07eb.906e after resume, -19
[   58.118153] usb 1-1.3.2: can't resume, status -19
[   58.118154] usb 1-1.3-port2: logical disconnect
[   58.118526] usb 1-1.3-port2: cannot disable (err = -71)

As you see in the 58.116035, the hub_resume and activate is OK for the
usb 1-1. The "usb 1-1.3: finish resume" is not in the log because it's not
considered suspended and no chance to ClearPortFeature. Then it fails
the subsequent hub 1-1.3 resume and active because the usb 1-1.3 happens
to be a downstream hub. So this is why we need at least udev->reset_resume
to give this kind of timeout port/device a chance to clear port feature and
come back from an unknown state.

Chris

> > Signed-off-by: Chris Chiu <chris.chiu@canonical.com>
> > ---
> >
> > Changelog:
> >   v2:
> >     - create a new variable to keep the result of hub_port_status
> >       when suspend timeout.
> >
> >  drivers/usb/core/hub.c | 15 +++++++++++++++
> >  1 file changed, 15 insertions(+)
> >
> > diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> > index b2bc4b7c4289..3c823544e425 100644
> > --- a/drivers/usb/core/hub.c
> > +++ b/drivers/usb/core/hub.c
> > @@ -3385,6 +3385,21 @@ int usb_port_suspend(struct usb_device *udev, pm_message_t msg)
> >               status = 0;
> >       }
> >       if (status) {
> > +             if (status == -ETIMEDOUT) {
> > +                     u16 portstatus, portchange;
> > +
> > +                     int ret = hub_port_status(hub, port1, &portstatus,
> > +                                     &portchange);
> > +
> > +                     dev_dbg(&port_dev->dev,
> > +                             "suspend timeout, status %04x\n", portstatus);
> > +
> > +                     if (ret == 0 && port_is_suspended(hub, portstatus)) {
> > +                             udev->reset_resume = 1;
> > +                             goto err_wakeup;
> > +                     }
> > +             }
> > +
> >               dev_dbg(&port_dev->dev, "can't suspend, status %d\n", status);
> >
> >               /* Try to enable USB3 LTM again */
> > --
> > 2.20.1
> >