linux-kernel - Re: [SERIAL] Don't optimise away baud rate changes when BOTHER is used

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Message-Id: <1181303307.2801.36.camel@pmac.infradead.org>
Date:	Fri, 08 Jun 2007 12:48:27 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org, paulus@...ba.org
Subject: Re: [SERIAL] Don't optimise away baud rate changes when BOTHER is
	used

On Fri, 2007-06-08 at 12:48 +0100, Alan Cox wrote:
> > It works fine. The only problem is that if I set a _standard_ baud rate
> > with BOTHER and then read it back with something that doesn't grok
> > BOTHER, I get it back just as I set it.
> 
> That seemed to me to be the right thing to do.
> 
> > It might be better if it was returning B38400, rather than BOTHER.
> > Should we be using tty_termios_encode_baud_rate() for TCGETS()?
> 
> You can't really do that as you get weird behaviour then when people do
> 
> 	tcgetattr
> 		|= BOTHER;
> 		speed = 19200;
> 	tcsetattr
> 
> later in the same app
> 
> 	tcgetattr
> 		speed = 38400
> 	tcsetattr
> 
> knowing that they set BOTHER already.

Hm, true.

> I guess you could add both ioctl sets anyway but the plan longer term is
> for glibc tcsetattr/getattr to do the right thing with the new ioctls in
> all cases, as the glibc interface already provides speed fields.

Even with glibc helping, I'm not sure I see how to do the right thing
for both the 'old' stty and the case you describe. We'll just have to
update stty _if_ we set arbitrary baud rates and want it to display
them.

-- 
dwmw2

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