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

[Helge Deller]

On 10/27/20 10:00 AM, Johan Hovold wrote:
> On Thu, Oct 08, 2020 at 08:16:02PM +0200, Helge Deller wrote:
>> On 10/8/20 5:21 PM, Johan Hovold wrote:
>>> On Tue, Sep 29, 2020 at 09:33:27PM +0200, Helge Deller wrote:
>>>> With a 4-port serial USB HUB with FT232BM chips the serial ports stop
>>>> working after a software suspend/resume cycle.
>>>> Rewriting the latency timer during the resume phase fixes it.
>
>>>> +static int ftdi_reset_resume(struct usb_serial *serial)
>>>> +{
>>>> +	struct usb_serial_port *port = serial->port[0];
>>>> +
>>>> +	if (tty_port_initialized(&port->port))
>>>> +		write_latency_timer(port);
>>>
>>> Why are you only doing this for open ports?
>>
>> I more or less copied it from another driver....
>>
>>>> +
>>>> +	return usb_serial_generic_resume(serial);
>>>> +}
>>>
>>> And if the device has been reset there may need to reconfigured the
>>> termios settings for open ports.
>>>
>>> Could you expand a bit on what the problem is here?
>>
>> 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.

Thanks!
Helge