Re: [PATCH 2/2] usb: gadget serial: Honour termios CLOCAL on disconnect

[Peter Hurley <peter-WaGBZJeGNqdsbIuE7sb01tBPR1lH4CV8@public.gmane.org>]

On 10/27/2014 09:38 AM, Felipe Balbi wrote:
> Hi,
> 
> On Sun, Oct 26, 2014 at 08:01:30PM +0200, Kyösti Mälkki wrote:
>> There are applications where it is desirable to not hangup ttyGS* when
>> USB disconnect is detected. USB host side of communication may
>> power-cycle periodically or there may be the actual need to physically
>> disconnect and reconnect USB cable temporarily.
>>
>> USB disconnects on serial gadget are comparable to loss of Carrier Detect
>> of conventional UARTs. With the change, if ttyGS* has termios CLOCAL flag
>> set, disconnect on USB does not hangup the TTY.
>>
>> Signed-off-by: Kyösti Mälkki <kyosti.malkki-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>> ---
>>  drivers/usb/gadget/function/u_serial.c | 9 +++++++--
>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
>> index 491082a..e68ffd7 100644
>> --- a/drivers/usb/gadget/function/u_serial.c
>> +++ b/drivers/usb/gadget/function/u_serial.c
>> @@ -1254,8 +1254,13 @@ void gserial_disconnect(struct gserial *gser)
>>  	gser->ioport = NULL;
>>  	if (port->port.count > 0 || port->openclose) {
>>  		wake_up_interruptible(&port->drain_wait);
>> -		if (port->port.tty)
>> -			tty_hangup(port->port.tty);
>> +		struct tty_struct *tty = port->port.tty;
> 
> declare above as Sergei said.
> 
>> +		if (tty) {
> 
> is there any situation where tty would be NULL here ?
> 
>> +			if (tty->termios.c_cflag & CLOCAL)
>> +				stop_tty(tty);
>> +			else
>> +				tty_hangup(tty);
> 
> this I'll defer to Greg who also maintains tty.

I'm curious what happens without stop_tty().

The tty is restartable from userspace with
    tcflow(fd, TCOOFF);
    tcflow(fd, TCOON);

Regards,
Peter Hurley
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