Re: [PATCH 1/2] tty/hvc_console: Add DTR/RTS callback to handle HUPCL control

[Hendrik Brueckner <brueckner@linux.vnet.ibm.com>]

Hi Benjamin,

On Fri, Oct 11, 2013 at 06:15:11PM +1100, Benjamin Herrenschmidt wrote:
> On Tue, 2013-07-02 at 17:07 +0200, Hendrik Brueckner wrote:
> > Introduce a new callback to explicitly handle the HUPCL termios control flag.
> > This prepares for a follow-up commit for the hvc_iucv device driver to
> > improve handling when to drop an established network connection.
> > 
> > The callback naming is based on the recently added tty_port interface to
> > facilitate a potential refactoring of the hvc_console to use tty_port
> > functions.
> 
> I only just noticed that ... oops. Why add those dtr_rts() calls ? We
> already have tiocmset in there which is used to set DTR on HVSI consoles
> such as hvc_opal when using hvsi_lib...
> 
> Any reason why a separate callback was needed ?

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.

Thanks and kind regards,
  Hendrik