linux-kernel - Re: 2.6.25.3: serial problem (minicom)

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Message-ID: <alpine.LNX.1.00.0806170511270.11745@hani.compact.internal>
Date:	Tue, 17 Jun 2008 05:50:09 -0500 (CDT)
From:	"R.L. Horn" <lists@...tcheap.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
cc:	linux-kernel@...r.kernel.org
Subject: Re: 2.6.25.3: serial problem (minicom)

On Mon, 16 Jun 2008, Alan Cox wrote:

> Whatever it implies the behaviour should not have changed between 2.6.24 
> and 2.6.25.

Okay, I think I may have figured this out.

serial8250_set_termios() (8250.c) gets a baud rate using 
uart_get_baud_rate() (serial_core.c) which returns 9600 if the termios 
rate is B0.

The function does some stuff.

Right before returning, it calls tty_termios_encode_baud_rate() with the 
abovementioned rate.  That function obediently changes the c_cflag baud 
bits from B0 to B9600.  Presumably, this causes confusion in other 
functions (they never know that B0 was set).

I've now changed:

   tty_termios_encode_baud_rate(termios, baud, baud);

to:

   if ((termios->c_cflag & CBAUD) == B0)
       baud = 0;
   tty_termios_encode_baud_rate(termios, baud, baud);

And everybody's happy, I guess.

It looks like the DECstation DZ driver (drivers/serial/dz.c) will have the 
same problem, but I believe the others are okay (as of 2.6.25.6).
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