Re: about serial console problem

From: Eric W. Biederman (ebiederm@xmission.com)
Date: Wed Jul 25 2001 - 03:52:06 EST


"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

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