linux-kernel - RE: Strange output on the console

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Message-ID: <1dcb185901f04a5ea2476a449e371167@AcuMS.aculab.com>
Date:   Fri, 25 Feb 2022 10:11:43 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Willy Tarreau' <w@....eu>
CC:     'Steven Rostedt' <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Petr Mladek <pmladek@...e.com>,
        "Sergey Senozhatsky" <senozhatsky@...omium.org>,
        John Ogness <john.ogness@...utronix.de>
Subject: RE: Strange output on the console

From: Willy Tarreau
> Sent: 25 February 2022 06:37
> 
> On Fri, Feb 25, 2022 at 06:12:35AM +0000, David Laight wrote:
> > From: Steven Rostedt
> > > Sent: 25 February 2022 04:01
> > >
> > > I've been noticing that my tests have been spitting out strange output on
> > > the console. It would happen at boot up and then clear up. It looks like
> > > something screwed up with the serial timing.
> > >
> > > Attached is a dmesg of one of my test runs as an example.
> > >
> > > I've noticed this on both 32 bit and 64 bit x86.
> > >
> > > I haven't had time to look deeper into this, but I figured I let you know
> > > about it.
> > >
> > > And it always seems to happen right after:
> > >
> > >   Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled
> > >
> > > Maybe this is a serial issue and not a printk one? :-/
> >
> > Looks very much like the serial baud rate is being reset.
> 
> I don't think it's the baud rate, characters are still readable, it
> looks more like a fifo being too short and causing lots of chars to
> be dropped.

Just before it recovers there is this output:
    ATaitoscic nitahi tuPiet mfba Ae:   aD nCt AH0 nP0
That is probably 'fifo not enabled'.

But the earlier output doesn't have many different characters in it.
Which is typical of the baud rate being wrong.

	David

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