linux-kernel - Re: serial flow control appears broken

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Date:	Fri, 27 Jul 2007 13:05:15 -0700
From:	Lee Howard <faxguy@...ardsilvan.com>
To:	Tilman Schmidt <tilman@...p.cc>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Robert Hancock <hancockr@...w.ca>,
	linux-serial@...r.kernel.org, tytso@....edu, rmk@....linux.org.uk,
	linux-kernel@...r.kernel.org
Subject: Re: serial flow control appears broken

Tilman Schmidt wrote:

>Lee Howard schrieb:
>  
>
>>So, does this explain why I wouldn't have a problem at 115200 bps with 
>>kernel 2.2.5 but why I do with 2.6.5 and 2.6.18?  Both hardware and 
>>software flow control work fine with 2.2.5 (meaning I don't see any 
>>error message and I don't have any data corruption), but neither works 
>>to avoid the "kernel: ttyS1: 1 input overrun(s)" and consequent data 
>>corruption issue in 2.6.5 nor 2.6.18.
>>
>>Was there some associated application change in tty handling that needed 
>>to occur between the 2.2 and 2.6 kernels to properly implement flow control?
>>    
>>
>
>Could this be related?
>
>http://lkml.org/lkml/2007/7/18/245
>
>Quote:
>"I've recently found (using 2.6.21.4) that configuring a serial ports
>(ST16654) which use the 8250 driver using setserial results in the
>UART's FIFOs being disabled (unless you specify autoconfig)."
>  
>

I'm not running setserial on the port, myself.  But to test to see if it 
is related, I included this code in the application:

#include <linux/serial.h>
....
struct serial_struct serial;
ioctl(modemFd, TIOCGSERIAL, &serial);
traceModemOp("modem xmit_fifo_size: %u", serial.xmit_fifo_size);

And I get this resulting logging:

"MODEM modem xmit_fifo_size: 16"

So it's clear from here that the xmit_fifo_size is set correctly on this 
system.

Thanks,

Lee.

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