about serial console problem

about serial console problem

[Barry Wu]

Hi, all,

I am porting linux 2.4.3 to our mipsel evaluation
board. Now I meet a problem. Because I use edown
to download the linux kernel to evaluation board.
I update the serial baud rate to 115200.
I use serial 0 as our console, and I can use
printk to print debug messages on serial port.
But after kernel call /sbin/init, I can not
see "INIT ...  ..." messages on serial port.
I suppose perhaps I make some mistakes. But when
I use 2.2.12 kernel, it ok.
If someone knows, please help me. Thanks!

Barry

__________________________________________________
Do You Yahoo!?
Make international calls for as low as $.04/minute with Yahoo! Messenger
http://phonecard.yahoo.com/

Re: about serial console problem

[Eric W. Biederman]

Barry Wu <wqb123@yahoo.com> writes:

> Hi, all,
> 
> I am porting linux 2.4.3 to our mipsel evaluation
> board. Now I meet a problem. Because I use edown
> to download the linux kernel to evaluation board.
> I update the serial baud rate to 115200.
> I use serial 0 as our console, and I can use
> printk to print debug messages on serial port.
> But after kernel call /sbin/init, I can not
> see "INIT ...  ..." messages on serial port.
> I suppose perhaps I make some mistakes. But when
> I use 2.2.12 kernel, it ok.
> If someone knows, please help me. Thanks!

It's a bug in init.  INIT clears the CREAD flag which means all reads
to the console will be dropped.  Why it /sbin/init works before 2.4.3
is a mystery.

Eric

Re: about serial console problem

[Robert J.Dunlop]

Hi,

On Tue, Jul 24,  Eric W. Biederman wrote:
> Barry Wu <wqb123@yahoo.com> writes:
> 
> > I am porting linux 2.4.3 to our mipsel evaluation
> > board. Now I meet a problem. Because I use edown
> > to download the linux kernel to evaluation board.
> > I update the serial baud rate to 115200.
> > I use serial 0 as our console, and I can use
> > printk to print debug messages on serial port.
> > But after kernel call /sbin/init, I can not
> > see "INIT ...  ..." messages on serial port.
> > I suppose perhaps I make some mistakes. But when
> > I use 2.2.12 kernel, it ok.
> > If someone knows, please help me. Thanks!
> 
> It's a bug in init.  INIT clears the CREAD flag which means all reads
> to the console will be dropped.  Why it /sbin/init works before 2.4.3
> is a mystery.

Perhaps because most of the serial drivers didn't implement CREAD (or
rather !CREAD) until then. Actually more and more have been implementing
it as we go through 2.4.x, depends when your particular driver got caught.

-- 
        Bob Dunlop                      FarSite Communications
        rjd@xyzzy.clara.co.uk           bob.dunlop@farsite.co.uk
        www.xyzzy.clara.co.uk           www.farsite.co.uk

Re: about serial console problem

[Eric W. Biederman]

"Robert J.Dunlop" <rjd@xyzzy.clara.co.uk> writes:

> Hi,
> 
> On Tue, Jul 24,  Eric W. Biederman wrote:
> > Barry Wu <wqb123@yahoo.com> writes:
> > 
> > > I am porting linux 2.4.3 to our mipsel evaluation
> > > board. Now I meet a problem. Because I use edown
> > > to download the linux kernel to evaluation board.
> > > I update the serial baud rate to 115200.
> > > I use serial 0 as our console, and I can use
> > > printk to print debug messages on serial port.
> > > But after kernel call /sbin/init, I can not
> > > see "INIT ...  ..." messages on serial port.
> > > I suppose perhaps I make some mistakes. But when
> > > I use 2.2.12 kernel, it ok.
> > > If someone knows, please help me. Thanks!
> > 
> > It's a bug in init.  INIT clears the CREAD flag which means all reads
> > to the console will be dropped.  Why it /sbin/init works before 2.4.3
> > is a mystery.
> 
> Perhaps because most of the serial drivers didn't implement CREAD (or
> rather !CREAD) until then. 

Hmm.  When I looked it appeared CREAD should have worked in 2.4.2 but I do
know /sbin/init didn't have a problem with that one.  

> Actually more and more have been implementing
> it as we go through 2.4.x, depends when your particular driver got caught.

Do you know the history on how/why ~CREAD support started showing in
in the linux kernels.  I'd like to understand what is going on.

Eric

Re: about serial console problem

[Robert J.Dunlop]

On Wed, Jul 25,  Eric W. Biederman wrote:
> "Robert J.Dunlop" <rjd@xyzzy.clara.co.uk> writes:
> > Actually more and more have been implementing
> > it as we go through 2.4.x, depends when your particular driver got caught.
> 
> Do you know the history on how/why ~CREAD support started showing in
> in the linux kernels.  I'd like to understand what is going on.

Sorry! I've red herringed you here. Most drivers were fixed way back in
2.2.x or before. From the Changelog we have:

  Fri Nov  8 20:19:50 1996  Theodore Ts'o  <tytso@rsts-11.mit.edu>
    * serial.c (change_speed): Add support for CREAD, as required by POSIX

I just happed to notice the late change on a couple of third party drivers
and jumped to the wrong conclusion.

-- 
        Bob Dunlop                      FarSite Communications
        rjd@xyzzy.clara.co.uk           bob.dunlop@farsite.co.uk
        www.xyzzy.clara.co.uk           www.farsite.co.uk