From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?UTF-8?B?S3nDtnN0aSBNw6Rsa2tp?= Subject: Re: [PATCH v2 2/2] usb: gadget serial: Honour termios CLOCAL on disconnect Date: Tue, 04 Nov 2014 01:49:48 +0200 Message-ID: <5458149C.8050203@gmail.com> References: <1414346490-19307-1-git-send-email-kyosti.malkki@gmail.com> <1415027885-2181-1-git-send-email-kyosti.malkki@gmail.com> <1415027885-2181-3-git-send-email-kyosti.malkki@gmail.com> <5457A062.50306@hurleysoftware.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <5457A062.50306-WaGBZJeGNqdsbIuE7sb01tBPR1lH4CV8@public.gmane.org> Sender: linux-usb-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Peter Hurley , linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Cc: linux-serial-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, balbi-l0cyMroinI0@public.gmane.org, gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org List-Id: linux-serial@vger.kernel.org On 11/03/2014 05:33 PM, Peter Hurley wrote: > Hi Ky=C3=B6sti, > > On 11/03/2014 10:18 AM, Ky=C3=B6sti M=C3=A4lkki wrote: >> There are applications where it is desirable to not hangup ttyGS* wh= en >> USB disconnect is detected. USB host side of communication may >> power-cycle periodically or there may be the actual need to physical= ly >> disconnect and reconnect USB cable temporarily. >> >> USB disconnects on serial gadget are comparable to loss of Carrier D= etect >> of conventional UARTs. With the change, if ttyGS* has termios CLOCAL= flag >> set, disconnect on USB does not hangup the TTY. >> >> Signed-off-by: Ky=C3=B6sti M=C3=A4lkki >> --- >> drivers/usb/gadget/function/u_serial.c | 11 +++++++++-- >> 1 file changed, 9 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/ga= dget/function/u_serial.c >> index 491082a..dabc165 100644 >> --- a/drivers/usb/gadget/function/u_serial.c >> +++ b/drivers/usb/gadget/function/u_serial.c >> @@ -1253,9 +1253,16 @@ void gserial_disconnect(struct gserial *gser) >> port->port_usb =3D NULL; >> gser->ioport =3D NULL; >> if (port->port.count > 0 || port->openclose) { >> + struct tty_struct *tty; >> + >> wake_up_interruptible(&port->drain_wait); >> - if (port->port.tty) >> - tty_hangup(port->port.tty); >> + tty =3D port->port.tty; >> + if (tty) { >> + if (tty->termios.c_cflag & CLOCAL) >> + stop_tty(tty); >> + else >> + tty_hangup(tty); > > It seems you missed my earlier email: what happens if you leave > out the stop_tty() call here? > Hi Peter I did not miss it. My intro to the patch series says I am not familiar=20 with tty infra, so I did not realize the question was directed to me. Also my setup with serial gadget runs kernel 3.12.6 so I cannot really=20 tell or test if tty changes since that would make my patch invalid or=20 unnecessary. In the previous change for gserial_disconnect(), where the tty_hangup()= =20 call was added, commit message described it fixes an endless loop on tt= y=20 device read and select. Would we be back at that situation without call= =20 to stop_tty()? > I ask because the tty is still restartable from userspace after you > stop_tty() here. So if your goal is to prevent write() from > happening, this won't work. There was no goal to prevent write() on the tty device, should there be= ?=20 Or should it silently just drop any characters while in the disconnecte= d=20 state instead of buffering (some of) them? Thanks, KM > > Regards, > Peter Hurley > >> + } >> } >> spin_unlock_irqrestore(&port->port_lock, flags); >> >> > -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html