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

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Date:	Sat, 12 Oct 2013 07:43:24 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>
Cc:	jslaby@...e.cz, gregkh@...uxfoundation.org,
	brueckner@...ux.vnet.com, heiko.carstens@...ibm.com,
	schwidefsky@...ibm.com, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH 1/2] tty/hvc_console: Add DTR/RTS callback to handle
 HUPCL control

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).

Cheers,
Ben.


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