On Tue, 2013-10-15 at 17:36 +0200, Hendrik Brueckner wrote: > Hi Benjamin, > > On Sat, Oct 12, 2013 at 07:43:24AM +1100, Benjamin Herrenschmidt wrote: > > On Fri, 2013-10-11 at 14:47 +0200, Hendrik Brueckner wrote: > > > The tiocmget/tiocmset callbacks are used to set and get modem status and > > > triggered through an tty ioctl. > > > > > > The dtr_rts() callback is different and it is used for DTS/RTS handshaking > > > between the hvc_console (or any other tty_port) and the tty layer. The tty > > > port layer uses this callback to signal the hvc_console whether to raise or > > > lower the DTR/RTS lines. This is different than the ioctl interface to > > > controls the modem status. > > > > Well, DTR at least is the same via both callbacks... Also normal handshaking > > is normally RTS/CTS, only some HW setups "hijacks" DTR for RTS (old Macs come > > to mind). > > Yep. DTR is changed in both callbacks but from different layers. The > tiocmget/tiocmset are triggered through the ioctl. The dtr_rts() callback is > called in hvc_close() to properly handle HUPCL to lower modem control lines > after last process closes the device (hang up). > > This is also done in the hvsilib_close() in hvsi_lib.c: > > /* Clear our own DTR */ > if (!pv->tty || (pv->tty->termios.c_cflag & HUPCL)) > hvsilib_write_mctrl(pv, 0); > > This is actually what the dtr_rts() callback should trigger and I wonder > whether it would be worth to introduce the dtr_rts() callback to encapsulate > the "hvsilib_write_mctrl(pv, 0);" call from above. > > On the other hand, the dtr_rts() callback is a good encapsulation to not > directly access the hp->tty to potentially prevent a layering violation. At > least for the hvc_iucv() I do not want to deal with the "underlying" tty layer > and introduce additional reference accounting. > > I hope this helps you to understand my rational for introducing the dtr_rts() > callback. I'm not sure :) We still end up basically with 2 callbacks to do the same thing ... change the DTR line. It's odd at best, I still don't quite see why hvc_console couldn't just use mctrl... Cheers, Ben. -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
