linux-kernel - Re: should RTS init in serial core be tied to CRTSCTS

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Date:	Wed, 7 Mar 2007 06:13:10 +0100
From:	"Oleksiy Kebkal" <lesha@...logics.de>
To:	"Krzysztof Halasa" <khc@...waw.pl>
Cc:	"Mike Frysinger" <vapier.adi@...il.com>, rmk@....linux.org.uk,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	linux-serial@...r.kernel.org,
	"Robin Getz" <rgetz@...ckfin.uclinux.org>
Subject: Re: should RTS init in serial core be tied to CRTSCTS

> > shouldnt TIOCM_RTS be passed down only when the 'r' is appended to the
> > boot cmdline ?
>
> How would it be useful?
>
> CRTSCTS is for CTS only (i.e., the transmission is paused when CTS is
> inactive), not for RTS. DTR and RTS should be active when the port is
> open even without CRTSCTS (= without handshaking), it's used for
> various purposes such as providing +12V to the device (and two pins
> can supply more power than one - sure, it isn't the best idea).

The name of the option is not CCTS, but CRTSCTS, isn't it? So, you may
not only want to pause own transmission when CTS is inactive, but to
control the transmission flow from the remote side. Why should RTS be
active when the port is open even without CRTSCTS? You may still
assert RTS manually if it is used to provide +12V to the device. But
as I understand it is not common use of this pin, isn't it?

And a question is not only about supporting legacy equipment but also
about embedded hardware where RTS/CTS handshaking is handshaking, not
something else...

-Oleksiy
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