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Date:   Tue, 19 Nov 2019 12:30:27 +0100
From:   Petr Mladek <pmladek@suse.com>
To:     Jonathan Richardson <jonathan.richardson@broadcom.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        gregkh@linuxfoundation.org, jslaby@suse.com,
        sergey.senozhatsky@gmail.com, linux-serial@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Scott Branden <scott.branden@broadcom.com>,
        Ray Jui <ray.jui@broadcom.com>,
        Srinath Mannam <srinath.mannam@broadcom.com>
Subject: Re: console output duplicated when registering additional consoles
Message-ID: <20191119113027.74lp3dsg5ftvylp4@pathway.suse.cz>
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On Mon 2019-11-18 13:38:04, Jonathan Richardson wrote:
> On Thu, Nov 14, 2019 at 8:33 PM Sergey Senozhatsky
> <sergey.senozhatsky.work@gmail.com> wrote:
> >
> > Gosh, that part of printk is really complex.
> >
> > On (19/11/14 10:57), Petr Mladek wrote:
> > > For a proper solution we would need to match boot and real
> > > consoles that write messages into the physical device.
> > > But I am afraid that there is no support for this.
> >
> > Wouldn't those have same tty driver?

Interesting idea. Well, do early consoles have tty driver?

> > ---
> >
> >  kernel/printk/printk.c | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> >
> > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> > index f1b08015d3fa..a84cb20acf42 100644
> > --- a/kernel/printk/printk.c
> > +++ b/kernel/printk/printk.c
> > @@ -2690,6 +2690,19 @@ static int __init keep_bootcon_setup(char *str)
> >
> >  early_param("keep_bootcon", keep_bootcon_setup);
> >
> > +static bool known_console_driver(struct console *newcon)
> > +{
> > +       struct console *con;
> > +
> > +       for_each_console(con) {
> > +               if (!(con->flags & CON_ENABLED))
> > +                       continue;
> > +               if (con->device && con->device == newcon->device)
> > +                       return true;
> > +       }
> > +       return false;
> > +}
> > +
> >  /*
> >   * The console driver calls this routine during kernel initialization
> >   * to register the console printing procedure with printk() and to
> > @@ -2828,6 +2841,9 @@ void register_console(struct console *newcon)
> >         if (newcon->flags & CON_EXTENDED)
> >                 nr_ext_console_drivers++;
> >
> > +       if (known_console_driver(newcon))
> > +               newcon->flags &= ~CON_PRINTBUFFER;
> > +
> >         if (newcon->flags & CON_PRINTBUFFER) {
> >                 /*
> >                  * console_unlock(); will print out the buffered messages
> 
> Thanks.

Jonathan, have you tried this patch, please?
Does it solve your problem?

Best Regards,
Petr