linux-kernel - Re: [PATCH] USB: serial: ftdi_sio: Fix serial port stall after resume

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Date:   Wed, 28 Oct 2020 16:01:05 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Helge Deller <deller@....de>
Cc:     Johan Hovold <johan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: serial: ftdi_sio: Fix serial port stall after resume

On Wed, Oct 28, 2020 at 03:54:35PM +0100, Helge Deller wrote:
> On 10/27/20 10:00 AM, Johan Hovold wrote:
> > On Thu, Oct 08, 2020 at 08:16:02PM +0200, Helge Deller wrote:

> >> My testcase is pretty simple:
> >> 1. I use e.g. "minicom -D /dev/ttyUSB2". Serial connection works.
> >> 2. I exit minicom.
> >> 3. I suspend the workstation: "systemctl suspend"
> >> 4. I wake up the machine and wait a few seconds.
> >> 5. I start "minicom -D /dev/ttyUSB2" again. No transfers on the serial port.
> >>
> >> With my patch the minicom serial communications does work.
> >> Another way to wake up the connection is to rmmod the driver and
> >> insmod it again.
> >
> > Weird indeed. If you exit minicom before suspend and no other process is
> > keeping the port open, then that write_latency_timer() above would never
> > be executed.
> >
> > Could you enable some debugging and provide a dmesg log from a test
> > cycle (open/close minicom, suspend/resume, open minicom)?
> >
> > 	echo file usb-serial.c +p > /sys/kernel/debug/dynamic_debug/control
> 
> I enabled the debugging and tried a few times, but somehow I can not
> reproduce the issue any longer.
>
> So, please drop my patch for now.

Good to hear the problem's gone. :) Let us know if you run into it
again.

Johan